Next Article in Journal
Microflow Nanoprecipitation of Positively Charged Gastroresistant Polymer Nanoparticles of Eudragit® RS100: A Study of Fluid Dynamics and Chemical Parameters
Previous Article in Journal
Effect of Steel Fibers on the Hysteretic Performance of Concrete Beams with Steel Reinforcement—Tests and Analysis
Previous Article in Special Issue
Acid Mesoporous Carbon Monoliths from Lignocellulosic Biomass Waste for Methanol Dehydration
Open AccessReview

Recent Progress on Fullerene-Based Materials: Synthesis, Properties, Modifications, and Photocatalytic Applications

by Sai Yao 1,2, Xingzhong Yuan 1,2,*, Longbo Jiang 1,2,*, Ting Xiong 1,2 and Jin Zhang 1,2
1
College of Environmental Science and Engineering, Hunan University, Changsha 410082, China
2
Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Changsha 410082, China
*
Authors to whom correspondence should be addressed.
Materials 2020, 13(13), 2924; https://doi.org/10.3390/ma13132924
Received: 12 May 2020 / Revised: 7 June 2020 / Accepted: 22 June 2020 / Published: 30 June 2020
(This article belongs to the Special Issue Advanced Carbon Materials For Catalytical Applications)

Abstract

Solar light is an inexpensive energy source making up for energy shortage and solving serious environmental problems. For efficient utilization of solar energy, photocatalytic materials have attracted extensive attention over the last decades. As zero-dimensional carbon nanomaterials, fullerenes (C60, C70, etc.) have been extensively investigated for photocatalytic applications. Due to their unique properties, fullerenes can be used with other semiconductors as photocatalyst enhancers, and also as novel photocatalysts after being dispersed on non-semiconductors. This review summarizes fullerene-based materials (including fullerene/semiconductors and fullerene/non-semiconductors) for photocatalytic applications, such as water splitting, Cr (VI) reduction, pollutant degradation and bacterial disinfection. Firstly, the optical and electronic properties of fullerene are presented. Then, recent advances in the synthesis and photocatalytic mechanisms of fullerene-based photocatalysts are summarized. Furthermore, the effective performances of fullerene-based photocatalysts are discussed, mainly concerning photocatalytic H2 generation and pollutant removal. Finally, the current challenges and prospects of fullerene-based photocatalysts are proposed. It is expected that this review could bring a better understanding of fullerene-based photocatalysts for water treatment and environmental protection.
Keywords: fullerene; visible-light photocatalysis; synthesis; H2 production; wastewater treatment fullerene; visible-light photocatalysis; synthesis; H2 production; wastewater treatment

1. Introduction

There is no denying that both environmental issues and the energy crisis are becoming serious threats to the sustainable development of human society, with the endless consumption of fossil fuels and the irregular discharge of anthropogenic action [1,2]. In order to solve these problems, industrial development must concentrate on clean energy alternatives, which reduce environmental pollution. As a renewable energy source, solar energy has been an intriguing option. Photocatalysts are an effective route to utilize solar energy for various chemical reactions, including photocatalytic pollutant degradation, disinfection, selective organic synthesis, reduction of CO2 and H2 generation. This is an attractive technology which could effectually utilize solar energy, generate clean production (H2) and remediate the environment. Since the photocatalytic performance of TiO2 for water splitting was proposed for the first time by Fujishima and Honda in 1970s, much work has been done to study the photocatalytic mechanisms and develop novel photocatalysts [3]. Up to date, numerous appealing photocatalysts have been developed and extensively investigated, such as simple oxides (ZnO) [4], metal chalcogenides (CdS) [5], Ag-based compound (Ag3PO4) [6], Bi-based compound (BiVO4 and Bi2MoO6) [7,8], MOFs [9] and g-C3N4 [10]. In addition to novel photocatalysts, cocatalysts such as precious metals (Pt), two-dimensional transition metal sulfides (MoS2, WS2, etc.) and carbonaceous nanomaterials are also widely developed and applied in the field of photocatalysis [11,12,13].
Since the mid-1990s, carbonaceous nanomaterials have been attracting extensive attention, including fullerene, carbon nanotube (CNT) and graphene [14]. Due to uniquely optical and electrical properties, they have been extensively investigated in photocatalytic applications in the past decades. On one hand, they could enhance the photocatalytic efficiency of other semiconductors after combination. For example, CNTs could induce photocatalytic enhancement via three mechanisms: increasing the surface area, suppressing the recombination of hole(h+)-electron(e) pairs and enhancing the adsorption of visible light) [15]. Similar to CNT, graphene covers all three of the mechanisms of photocatalytic enhancement above. On the other hand, carbonaceous nanomaterials display effective photocatalytic performance on their own without combining with other semiconductors and are applied alone as novel photocatalysts in some cases. For example, Luo, et al. [16] proposed a self-photocatalytic activity of multiwalled nanotubes (MWCNTs) in the visible range after highly defective modification. Moreover, modified graphene oxide (GO) with a band gap of 2.4−4.3 eV exhibits effective H2 generation ability within light illumination (UV or visible), which alone may be regarded as a next-generation photocatalyst [17,18].
Among carbonaceous nanomaterials, fullerene exhibits appealing performances similar to CNT and graphene in the photocatalytic application. In previous studies, extensive attentions have been devoted to exploring the roles that fullerene plays in the photocatalytic processes. It was proven that fullerene can be used not only as a photocatalytic enhancer for other semiconductors but also as a novel photocatalyst itself, after being dispersed on a non-semiconductor support. This is ascribed to its distinct optical, photophysical and photochemical properties. Fullerene, a carbon allotrope, is a kind of zero-dimensional (0D) nanocarbon material discovered by Kroto et al., and it has a closed-cage spherical structure which consists of five-membered and six-membered rings [19]. It is well established that there are various forms of fullerene, such as C60, C70, C76, C82 and C84. Among these forms, the C60 and C70 were more extensively investigated than others. Owing to electron delocalization, fullerenes are used extensively as strong-affinity electron acceptor, and for instance C60 is able to reversibly absorb six electrons [20]. The band gap energy (Eg) of solid fullerenes (such as C60, C70, C84 etc.) are from 1.5 to 1.98 eV between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) [4]. Ascribed to the narrow Eg, fullerenes have intensive absorption of UV light and moderate but extensive adsorption of visible light, which make them appealing options for photocatalytic application. Additionally, fullerenes have been previously reported as an excellent photosensitizer as well, with a high quantum efficiency around 1.0 [21]. Fullerene solutions can induce photochemical reactive oxygen species (ROS) generation via two pathways. Under light irradiation (UV or visible), single oxygen (1O2) will be formed in fullerene-toluene solution (pathway II), and superoxide anion radical (O2−•) and hydroxyl radical (•OH) can be generated in solvent in the presence of electron donors such as ethylenediamine tetraacetic acid (EDTA) and nicotinamide adenine dinucleotide (NADH) [22]. Typically, ROS is a class of active materials that easily induce chemical reaction, which could play an effective role in photocatalytic application. However, easy aggregation is the main obstacle of fullerene in water treatment applications, which suppresses the photoactivity of fullerene. Namely, when dispersed in water, fullerene tends to form nanoscale aggregates (termed nC60, nC70, etc.) with the quenching of excited states of neighboring fullerene molecules which are brought into close contact via aggregation. For retaining fullerene’s photoactivity in aqueous systems, it is necessary for immobilization of fullerene onto solid supports.
Nowadays, many fullerene-semiconductor materials have been successfully built for photocatalytic applications, such as TiO2/C60 (C70), ZnO/C60, CdS/C60 and C3N4/C60 (C70) [23,24,25]. These photocatalysts have been extensively investigated in photocatalytic pollutant degradation, disinfection and water splitting for H2 evolution. Note that fullerene can obviously enhance the photocatalytic efficiency. At the same time, a variety of fullerene-support (non-semiconductor) materials were successfully fabricated and used for photodegradation of organic pollutant, photocatalytic organic synthesis and disinfection, such as silica/C60, γ-Al2O3/C60, MCM-41/C70 and polysiloxane-supported fullerene derivative [26,27,28]. Apart from high-efficient photocatalytic activity, these photocatalysts not only exhibited more stable than the pristine fullerene in solution but also had superior recyclability.
Previously, Yeh, Cihlář, Chang, Cheng and Teng [13] have reviewed the roles of graphene oxide (GO) in photocatalytic water splitting, which mainly introduces strategies for tuning the electronic structure of GO for photocatalytic water splitting. Gangu, Maddila and Jonnalagadda [15] have reported a review on the MWCNTs mediated semiconducting materials as photocatalysts in water treatment. In another review, Ge, Zhang and Park [14] have discussed recent advances in carbonaceous photocatalysts and the developmental direction for them, such as activated carbon, carbon dots, carbon nanotubes, graphene and fullerene. To our knowledge, no papers have reviewed the fullerene/semiconductor and fullerene/support photocatalysts for wastewater treatment and water splitting. Therefore, the present review provides a comprehensive understanding of fullerene-based photocatalysts, including fullerene/semiconductor photocatalysts and fullerene/support photocatalysts. The optical, photochemical and electronic properties of fullerene are generally presented. Then, recent advances in the synthesis methods and photocatalytic application of fullerene-based photocatalysts are summarized. Meanwhile, the photocatalytic efficiency of these-prepared photocatalysts are discussed in wastewater treatment and water splitting for H2 evolution, wherein the mechanisms of the fullerene-based photocatalysts are underlined in detail. In the end, the current challenges and prospects of fullerene-based photocatalysts are proposed.

2. Role of Fullerene

2.1. Basic Principles of Semiconducting Photocatalysis

In the photocatalytic procedure of semiconductors, there are three main factors, i.e., light resources, photocatalysts and reaction mediums [14]. The photocatalytic process could be initiated only by the light (i.e., UV, infrared and visible light) with energy equal to or over the band gap energy (Eg) of the photocatalyst. Typically, it could be briefly presented as follows. Upon irradiation by light resource, the electrons in the valence band (VB) could be excited to the conduction band (CB) of the photocatalyst and holes leave in VB, resulting in the separation of photogenerated hole-electron pairs. Immediately, most of them recombine with heat generation while a small fraction can transfer to the semiconductor’s surface to induce redox reactions. Generally, for photocatalytic decontamination, the separated holes and electrons of the semiconductor can react with ambient substances (i.e., H2O and O2) to produce free radicals (i.e., •OH, •O2, HO2•, H2O2). Then, the highly oxidative holes and reactive radicals will intensively degrade organic pollutants into small molecules or inorganic materials through addition/substitution reaction and electron transfer between contaminants and free radicals [29]. Through the processes above, the pollution is mitigated or eliminated. Compared with pollutant degradation, the photocatalytic H2 generation over semiconductor share some similarities. In detail, the generating processes of the photoinduced charges and formation of partial radicals are identical between pollutant degradation and H2 generation. The difference in photocatalytic H2 generation is that photoinduced charges react with H+ adsorbed on the photocatalyst or in surroundings to produce H2 rather than •O2 [30]. In this process, additives are usually required to facilitate the efficiency of photocatalytic H2 generation, such as hole scavenger and (or) sacrificial donor.
In the past decades, a number of semiconductors were developed for photocatalysis applications, such as TiO2, ZnO, CdS, Ag-based semiconductors, Bi-based semiconductors and g-C3N4. However, many problems limit the photocatalytic efficiency of the current photocatalysts, including insufficient visible light utilization, wide bandgap, rapid recombination of photoinduced holes and electrons and poor stability. Various strategies were proved to be effective in enhancing the photocatalytic activity, such as morphology control, element doping, heterojunction construction and coupling with carbonaceous nanomaterials [10].

2.2. The Role of Fullerene in Semiconductor/Fullerene Photocatalysts

For effective semiconductor/fullerene photocatalysts, the introduction of fullerene generally enhances the photocatalytic performance through various aspects as follows. For instance, fullerene could capture electrons from CB of semiconductor due to its high-affinity for electrons, which significantly retard the recombination of photoinduced hole-electron pairs [31,32]. As a result, more separated photogenerated holes and electrons could take part in photocatalytic reaction, increasing photocatalytic efficiency. Then, fullerene could enhance the light absorption (both UV and visible light) because it is an excellent photo-response material (300~700 nm), wherein elevated light energy utilization excites more electrons from VB to CB [33,34]. In respect to photo-response characteristics, it must also be mentioned that fullerene could not shift the adsorption edge of pristine photocatalyst unless the introduction of fullerene changed the structure of semiconductor [35,36,37]. In other words, if the fullerene does not change the crystalline structure of semiconductor in the synthesis procedure, which was typically affected by a stronger bonding force other than simply physically blending, it could not change the conduction band (Eg) at all. Undoubtedly, the introduction of fullerene could change the specific surface area BET (Brunauer–Emmett–Teller), while it does not always present the same results of change trend. In previous studies, it increased or decreased the BET of the photocatalyst depending on the specific situation [38,39,40]. So, it was controversial that the fullerene enhances the BET of photocatalyst to contribute to high adsorption ability for reactant.
Fullerene is virtually insoluble in water, but soluble in nonpolar organic solvents, such as toluene and 1,2-dichlorobenzen [41]. Hence, it performs a good stability in water solution. After dissolved in nonpolar solvent, fullerene could be coupled with semiconductor to form stable semiconductor/fullerene composite by various methods, wherein no fullerene is leached out even after the as-prepared composite is repeatedly rinsed with the aforementioned solvent. Additionally, fullerene exhibits superior potentials for stabilizing semiconductors which deeply suffers photocorrosion, such as ZnO, CdS and Ag3PO4. For example, a significant increase of stabilization was observed for ZnO/C60 nanocomposite in previous studies [42]. The photogenerated holes of ZnO could easily react with surface oxygen atoms during the photocatalysis process, leading to fast decline of photocatalytic activity. When C60 was covered on ZnO, the activity of surface oxygen atoms was effectively reduced so that photocorrosion effect was effectively inhibited. Similarly, high stabilization of AgPO4/C60 was also observed, because C60 could obviously suppress the transform of Ag+ into Ag of bare Ag3PO4 composite [6]. Moreover, Cai, et al. [43] fabricated CdS/C60 nanocomposite in which C60 has shown effectively inhibition of photocorrosion of CdS. In order to estimate the stability of the as-prepared sample, the released Cd2+ concentration was determined in remaining solution after three cycles for rhodamine (RhB) degradation. The Cd2+ concentration was 381.3 µg/L in solution with naked CdS while it was 51.9 µg/L in solution with 0.4C60/CdS nanocomposite, and the former was 7.3-times of the later. This means that C60 could effectively inhibit the photocorrosion to enhance the stability of CdS.

3. Synthesis of Semiconductor/Fullerene Photocatalysts

A number of fullerene/semiconductors (TiO2, ZnO, CdS, C3N4, etc.) have been fabricated for photocatalytic wastewater treatment and water splitting. It is unquestionable that synthetic process plays an important role in determining the size, morphology and physicochemical characteristic of a photocatalyst. Fullerene/semiconductor photocatalysts can be constructed via a series of synthetic methods, including simple adsorption, hydrothermal/solvothermal synthesis, sol-gel procedure and mechanical ball-milling. These synthetic methods are summarized and illustrated briefly as follows.

3.1. Simple Adsorption Method

Simple adsorption method has been extensively used to fabricate semiconductor/fullerene nanocomposites. This procedure is cost-effective without complicated external condition. It is well established that pure fullerene (C60 or C70) is extremely hydrophobic but dissolves in some organic solvents (benzene, toluene, 1,2-dichlorobenzen etc.), which are mainly used to dissolve fullerene for preparing fullerene/semiconductor photocatalysts [4,44]. Typically, the semiconductor is added into the fullerene solution to form adequately dispersed suspensions, and then the newly generating fullerene/semiconductor nanocomposite is obtained through evaporating the solvent. Many semiconductor/fullerene nanocomposites have been synthesized through this method, such as TiO2/C60, ZnO/C60, Bi-based oxides/C60 and C3N4/C60 [45,46,47]. Note that the simple adsorption method differs from direct mechanical mixture, because no fullerene is leached out when the nanocomposite is added into the aforementioned organic solvent.

3.2. Hydrothermal Synthesis Method

Hydrothermal synthesis is an appealing method for preparing semiconductor/fullerene nanomaterials. In the synthetic procedure, pretreatment of fullerene is imperative and acid-treatment is extensively applied to produce several oxygen-containing active sites on the surface of fullerene. For instance, nitric acid is a common agent to oxide fullerene under reflux condition, further facilitating more efficient combination of fullerene with other semiconductors through hydrothermal procedure. Yu, et al. [48] constructed TiO2/C60 nanocomposite using this acid-treated C60 via a hydrothermal method. Activated C60 and Ti(OC4H9)4 (titanium source) were mixed into ethanol/water solution (1:2 v/v) and then the reaction mixture solution was transferred into stainless steel autoclave at 180 °C for 10 h. Similarly, TiO2/C70 was fabricated by a hydrothermal procedure as well [49]. Very recently, several semiconductor/fullerene photocatalysts were obtained by the hydrothermal method, such as CdS/C60, PbMoO4/C60, BiOCl/C70 and C3N4/(C60, C70) [50,51]. For example, Cai, Hu, Zhang, Li and Shen [43] constructed CdS/C60 photocatalyst via a facile one-pot hydrothermal method, wherein a mixture of acid-treated C60, Cd(CH3COO)2·2H2O and L-cysteine in water was heated at 200 °C for 10 h in autoclave. Moreover, Ma, Zhong, Li, Wang and Peng [39] synthesized BiOCl/C70 photocatalyst via a hydrothermal method and the procedure was presented as follow. Acid-treated C70 and Bi(NO3)3∙5H2O were dissolved in glacial acetic acid and KCl solution was slowly added into, and then the mixture solution was transferred into stainless autoclave maintaining at 180 °C for 24 h.
In addition to nitric acid, meta-chloroperoxybenzoic acid (MCPBA) is an effectively alternative oxidizing agent to pretreat fullerene before hydrothermal method. Typically, fullerene and MCPBA are dissolved into benzene, followed by heating reflux for hours to activated the surface of fullerene. For instance, CoS/C60 nanocomposite was prepared by using the MCPBA-oxidized C60 via hydrothermal method [52]. Namely, MCPBA-oxidized C60, CoCl2 and Na2S2O3 mixture water solution was heated at 150 °C for 12 h in autoclave, and the CoS/C60 nanocomposite was obtained through filter. Similarly, other semiconductor/fullerene nanocomposites were prepared via hydrothermal method with MCPBA-oxidized C60, including CdSe/C60 and WO3/C60 [36,53].

3.3. Ball Milling Method

Ball-milling is a facile and eco-friendly method to structure solid–solid composites, which could generate stronger intermolecular interactions than physical blends. Recently, the hybridized MoS2/C60 nanocomposite was obtained through a planetary ball-milling machine [54]. Mixture of MoS2 and C60 powders was transferred into a ball-milling jar together with stainless steel balls under Ar atmosphere. After operation at 500 rmp for 48 h, the reactant was Soxhlet extracted by CS2 to remove the unreacted C60. The strong van der Waals (vdW) interactions contributed to formation of MoS2/C60 heterostructure rather than a covalent conformation, resulting in elevated photocatalytic activity of pure MoS2. In addition, a g-C3N4/C60 nanocomposite was fabricated via a ball-milling route as well [55]. Additional LiOH was needed as a catalyst before ball-milling process and the detailed synthetic process of the g-C3N4/C60 was presented in Figure 1. It was firstly proposed in fullerene chemistry that the covalent bonding forms via a four-membered ring of azetidine between C60 and g-C3N4 nanosheets. The LiOH as catalyst breaks π-π carbon bonds of C60 to produce C60 radicals, then ball-milling activates g-C3N3 and results in the covalent reaction between g-C3N4 and C60 (Figure 1).

3.4. Other Techniques

Sol-gel approach has been used to prepare fullerene-TiO2-semiconductor ternary photocatalysts. Meng, et al. [56] fabricated CdS-C60/TiO2 photocatalyst by a sol-gel method. Firstly, NaS2 solution was dropwise added into oxidized C60 and (CH3COO)2Cd·2H2O mixed ethanol solution and the collected solids were calcinated at 300 °C to obtain CdS-C60 particles. Then, CdS-C60 particles were added into titanium (IV) n-butoxide (TNB) solution with constant stirring and CdS-C60/TiO2 gels were produced in mixed solution under reflux at 70 °C. Finally, the CdS-C60/TiO2 nanoparticles were obtained after heat treatment at 400 °C. Bai, Wang, Wang, Yao and Zhu [35] proposed a facile thermal treatment method for fabricating g-C3N4/C60 photocatalyst. The procedure was presented as follow: ball-milled C60 and dicyandiamide mixture was transferred into a muffle furnace and held at 550 °C for 4 h. Moreover, Li and Ko [57] successfully prepared MoS2/C60 nanocomposite by a facile heating treatment procedure. The wetness impregnation method is also an effective method for building semiconductor/fullerene photocatalysts. Apostolopoulou, et al. [58] prepared TiO2/C60 nanoparticles using 1,2-dichloro-benzene as a solvent via a successive incipient wetness impregnation followed by heating at 180 °C. Similarly, a polyhydroxyfullerene (PHF)/titanium dioxide nanotube was prepared by incipient wetness impregnation [59]. Firstly, fullerene was functionalized by NaOH and H2O2 to obtain PHF (or called fullerenol). Then, PHF was added to TiO2 nanotube solution under a wetness impregnation followed by heating at 400 °C. Hence, this provides a new route for coupling fullerenol with other semiconductors to obtain effective photocatalysts.

4. The Photocatalytic Application of Fullerene/Semiconductor Photocatalysts

The fullerene/semiconductor photocatalysts have been extensively used for photocatalytic wastewater treatment (pollutant degradation, Cr (VI) reduction, disinfection etc.) and water splitting for H2 generation [49,60,61]. Among them, photocatalytic degradation of organic pollutant is ascribed to decomposition of organic molecule structure and photocatalytic disinfection depends on inactivation of microorganisms. However, photocatalytic Cr (VI) reduction focuses on the transformation from Cr (VI) to Cr (III). It is generally believed that chromium (Cr) is among the sixteen most toxic contaminants due to its carcinogenic and teratogenic effect on human. Hence, the World Health Organization (WHO) and the United State Environmental Protection Agency (USEPA) have set the maximum permissible concentration of Cr in drinking water at 0.05 mg/L and 0.1 mg/L [62]. Note that the reduced Cr (III) is far less toxic and more stable than Cr (VI), so the photocatalytic Cr (VI) reduction is a promising method to reduce the chromium toxicity in water.
Furthermore, Table 1 and Table 2 summarize the photocatalytic efficiency in pollutant degradation and H2 generation over all kinds of fullerene/semiconductor photocatalysts, respectively. Next, detailed photocatalytic activity and mechanisms will be discussed for various types of semiconductor/fullerene photocatalysts, which is accompanied with analyses of electron transfer routes, free radical reactions and stability of photocatalysts.

4.1. Fullerene Based TiO2 Photocatalysts

TiO2 is the most extensively used photocatalyst due to its easy availability, strong oxidizing ability, and superior photoelectronic properties [63,64]. With a wide band gap (~3.2 eV), TiO2 could only be excited under UV light, which limits efficient utilization of solar light [65]. Meanwhile, the fast recombination of photoinduced hole-electron pairs restricts the photocatalytic efficiency of TiO2 [66]. It has been proven that coupling fullerene with TiO2 is a helpful way to boost the photocatalytic efficiency of pure TiO2 both under UV light and visible light irradiation.
Oh, et al. [67] prepared TiO2/C60 photocatalyst by a heat treatment method with 700 °C. It was shown that the TiO2/C60 exhibited a more significant effect towards MB degradation with an increase of −ln (C/C0) values than that of the original TiO2 under UV light illumination. Yu, Ma, Liu and Cheng [48] successfully fabricated mesoporous TiO2/C60 powders via a hydrothermal method, which demonstrated that C60 molecules could be dispersed as monolayer or few layers onto bimodal mesoporous TiO2 via covalent bonding. The 0.5 wt % TiO2/C60 exhibited the best photocatalytic efficiency for acetone decomposition under UV light irradiation and the degradation rate constant (k) was 13.9 × 10−3, reaching 3.3-times that of the pure TiO2. In this UV-light-driven photocatalytic system, the dominant role of C60 is an inhibitor of rapid recombination of photogenerated hole-electron pairs, leading to boost the quantum efficiency of TiO2. With respect to TiO2/C60 photocatalyst, the excited electrons will transfer from TiO2 to C60 because the conduction band potential of TiO2 (−0.5 V vs. NHE) is more negative than that of C60/C60•− (−0.2 V vs. NHE). Under UV light irradiation, the photogenerated electrons are excited from the VB of TiO2 to the CB, leaving holes in the VB. Generally, these holes and electrons incline to fast recombination and only partial carriers take part in redox. However, after C60 is tightly coupled with TiO2, excited electrons could further transfer to C60 due to its excellent electron adsorption capacity, which effectively inhibits recombination of photoinduced carriers and supplies more carriers participating in photocatalytic reaction. Besides, C60 derivative (C60(CHCOOH)2) modified TiO2 nanoparticles fabricated by Mu, Long, Kang and Mu [61] showed superior photocatalytic efficiency in Cr (VI) reduction under UV light illumination. Compared with pristine TiO2, the C60-derivative-modified TiO2 nanocomposites exhibited a higher photocatalytic efficiency of 97% for Cr(VI) reduction within 1.5 h UV irradiation. The electron transfer and radical formation procedure is presented as follows, in Equations (1)−(3):
TiO 2 / C 60 h v C 60 ( e ) / TiO 2 ( h + )
TiO 2   ( h + ) + OH TiO 2 + OH
C 60 ( e ) + O 2 C 60 + O 2
In addition to UV-light-driven photocatalytic activity, TiO2/C60 nanocomposites also exhibit superior photocatalytic capacity under visible light irradiation. In this visible-light-driven photocatalytic system, the introduced C60 could typically enhance the photocatalytic activity in two ways at the same time: one is to increase the visible light adsorption, the other is to prolong the lifetimes of photoinduced carriers for participating redox reaction. For example, an investigation was conducted into the visible-light-induce photocatalytic activity of TiO2/C60 towards MB degradation [88]. In this study, two crystals of TiO2 (anatase and rutile) were coupled with C60 to assemble photocatalysts and the rutile-C60 exhibited significantly superior efficiency than pristine rutile under visible illumination. Grandcolas, et al. [89] synthesized C60 modified TiO2 nanotubes via a simple impregnation method using ethanol and toluene as co-solvents, and the as-prepared sample exhibited superior efficiency in photocatalytic isopropanol degradation under visible light irradiation. More recently, a polycarboxylic acid functionalized fullerene (C60-(COOH)n) was coupled with TiO2 to obtain a novel photocatalyst TiO2/C60 nanocomposite via ultrasonication-evaporation method for the first time [68]. For the as-prepared photocatalysts, the introduction of C60 obviously decreased the aggregation of pure TiO2 nanocomposites (Figure 2a,b), and the C60 particles were well-dispersed and closely contacted onto the surface of TiO2 (Figure 2c). Compared with pure TiO2, the 1 wt % TiO2/C60 exhibited stronger both UV and visible light absorption, resulting in improving the utilization of light energy (Figure 2d). In order to trace oxidative species involved in the photocatalytic reaction, in situ radical trapping experiments were made, wherein EDTA was used for trapping holes and 1,4-benzoquinone (BQ) was a scavenger for •O2. In the presence of EDTA, the photocatalytic degradation efficiency to RhB was dramatically retarded, and a similar trend was also observed with BQ addition (Figure 2e). These results meant that the photoinduced h+ and •O2 were involved in the photocatalytic reaction. Under visible light illumination for 150 min, 1 wt % TiO2/C60 nanocomposite showed 95% degradation efficiency to RhB, which was significantly higher than pristine TiO2 (Figure 2f). To further check the stability of the TiO2/C60 photocatalyst, the recovered composite was used for repeatedly photocatalytic degradation experiment towards RhB. After five repeated experiments under visible light irradiation for 150 min, the degradation efficiency decreased from 95% to around 80%. There is no doubt that the long-term stability of photocatalysts is particularly vital to practical application. Therefore, future work could focus on the synthesis method of TiO2 to improve the stability of TiO2/C60 photocatalysts. For example, Bastakoti, et al. [90] reported a high-efficiency method to fabricate more stable mesoporous metal oxides (including TiO2, Ta2O5 and Nb2O5).
Compared to TiO2, C70 is a close-shell configuration consisting of 35 bonding molecular orbitals with 70 p-electrons [91]. Similar to C60, C70 has higher electron acceptability and higher efficiency of light harvesting over TiO2 [92,93]. Thus, C70 is a promising alternative to boost the photocatalytic efficiency of TiO2. Cho, et al. [94] fabricated both TiO2/C60 and TiO2/C70 nanowire to estimate their photocatalytic activity. In this study, TiO2/C70 showed a significantly stronger absorbance within 400~650 nm and a lower photoluminescence spectra (PL) than TiO2/C60. This means the C70 displayed better efficiency in boosting visible light absorption and inhibiting recombination of hole-electron pairs than C60. Accordingly, the TiO2/C70 nanowire displayed higher photocatalytic activity for MB degradation than TiO2/C60 in the visible light irradiation. Furthermore, Wang, Liu, Dai, Cai, Chen, Yang and Huang [69] assembled TiO2-C70 hybrids using acid-treated C70, Ti(SO4)2 and cetyltrimethylammonium bromide (CTAB) by a hydrothermal method. It was proven that the 8.5 wt % TiO2-C70 showed the best photodegradation efficiency to sulfathiazole under visible light, which was 4.2 times that of TiO2 + C70 mixture and 1.6 times that of the corresponding TiO2-C60 nanocomposite, respectively. The SEM and TEM images of 18 wt % TiO2-C70 nanocomposite are shown in Figure 3a,b. After C70 introduction, the surface of TiO2-C70 nanocomposites were uneven, which could increase the BET of the as-prepared samples. The C70 particles were well-dispersed onto the outer boundary of TiO2 composites, and it was estimated that a monolayer of C70 was covered onto the surface of TiO2. Additionally, the TiO2-C70 exhibited better light absorption and higher separation efficiency of hole-electron pairs than those of TiO2-C60 and pure TiO2 (Figure 3c,d). It is important to highlight that novel mechanisms of TiO2/fullerene were proposed for photocatalytic pollutant degradation [69]. From two aspects, UV light and visible light irradiation, the mechanisms are described as follows. Under UV light illumination, electrons are excited from VB to CB of TiO2, leaving holes in the VB. Then the CB electrons of TiO2 could rapidly transfer to C70, because the CB potential of TiO2 (0.5 V vs. NHE) is more negative relative to C70/C70 (0.2 V vs. NHE). In the meantime, the ground-state C70 is excited to a transient-state 1C70*, then undergoes rapid intersystem crossing (ISC) to a lower lying triplet state 3C70*. In this system, excited electrons can be injected into the three-states transform procedure of C70, resulting in suppression of their falling back to the VB of TiO2. Hence, this process effectively inhibits the recombination of photoinduced hole-electron pairs, so as to elevate the photocatalytic activity of TiO2/C70 nanocomposite (Figure 3e). On the other hand, a viewpoint of mid-gap band was proposed for TiO2/C70 with respect to the visible-light-driven photocatalytic mechanism. It was pointed out that the mid-gap band came into being between TiO2 and C70 ascribing to the strong chemical boning of these two materials. The electron transfer route was obviously distinct from those TiO2/fullerene photocatalysts in previous studies. Namely, visible light excites electrons from the VB of TiO2 to the mid-gap band and then from the mid-band to the CB of TiO2, leaving holes in the VB (Figure 3e). This procedure significantly prolongs the lifetime of the photoinduced carriers and facilitates the separation of hole-electron pairs for participating in photocatalytic reaction. Accordingly, the effectively separated holes and electrons participate in generation of reactive radical species. The e could react with dissolved O2 to produce •O2 and h+ react with H2O to produce •OH, then these radical species cause the degradation of sulfathiazole. To research the stability of TiO2/C70 nanocomposite, the recycled sample was dried for subsequently repeated experiments. After 5 runs (totally 15 h visible light illumination), the degradation efficiency to sulfathiazole over TiO2/C70 slightly declined, remaining over 90%. This evidenced that the aforementioned hydrothermal method was effective in building stable TiO2/fullerene photocatalysts.
Oh and Ko [95] fabricated Pt-fullerene/TiO2 nanocomposites via in-situ growth method using Pt-treated oxidized fullerene and TNB. Firstly, fullerene was oxidized by MCPBA and treated through ion exchange using potassium hexachloroplatinate (IV) (K2[PtCl6]), wherein Pt-treated oxidized fullerene was obtained. Then, Pt-fullerene was added into TNB solution (titanium source) for fabricating Pt-fullerene/TiO2 nanocomposite via a sol-gel method under mild condition (50 °C). The as-prepared sample exhibited elevated performance under UV light and the order of photocatalytic efficiency for MB degradation was: Pt-fullerene/TiO2 > fullerene/TiO2 ˃ pristine TiO2, due to the synergetic effects of Pt, oxidized-fullerene and TiO2. In this study, it was proposed that Pt-fullerene was homogeneously covered with TiO2 particles, wherein TiO2 would be mounted in a 3-dimensional matrix. It was concluded that three factors contributed to the superior photocatalytic activity of Pt-fullerene/TiO2, including photocatalytic reaction of the supported TiO2, decomposition of the organo-metallic reaction by the Pt compound and energy transfer effects of fullerene. Through the same method, a number of metal-treated fullerene/TiO2 composites were prepared for photocatalytic application as well, such as Fe-C60/TiO2, V-C60/TiO2 and Pd-C60/TiO2 [96,97]. For instance, Meng, Zhang, Zhu, Park, Ghosh, Choi and Oh [76] fabricated M-fullerene/TiO2 (M representing Pt, Y or Pd) composites to compare their photocatalytic efficiency. Among these samples, the Pd-fullerene/TiO2 showed the best photocatalytic activity for MB decomposition under UV light, due to its better dispersion and larger BET surface over the Pt-fullerene/TiO2 and Y-fullerene/TiO2. Further results indicated that the synergistic effects between Pd and fullerene improves the photocatalytic activity of TiO2, including enhancement of light adsorption by fullerene and Pd as the final electron-acceptor. More recently, Islam, Hangkun, Ting, Zubia, Goos, Bernal, Botez, Narayan, Chan and Noveron [77] prepared AuNPs-TiO2-C60 composites, wherein the introduction of C60 significantly boosts the photoactivity and photostability of AuNPs-TiO2. It was reported that C60 played threefold roles in the preparation of AuNPs-TiO2-C60. The introduction of C60 decreased the size of AuNPs (5 nm) and effectively prevented its agglomeration on the surface of TiO2, as well as linked AuNPs to TiO2 surface without any functionalization. The AuNPs-TiO2-C60 had a broader light adsorption region over pristine TiO2 and AuNPs-TiO2 nanocomposites, ranging from 500 to 650 nm. The 4.76% optimal AuNPs-TiO2-C60 sample showed 95% photodegradation efficiency towards MO after visible light irradiation for 160 min, which was 2 times higher than pristine TiO2.
Meng and his co-workers assembled a series of semiconductor/fullerene/TiO2 ternary photocatalysts via sol-gel method, such as TiO2/CdS/C60, TiO2/CdSe/C60 and TiO2/WO3/C60 nanocomposite [56,78,98]. For example, the TiO2/CdS/C60 photocatalyst exhibited superior efficiency in photocatalytic pollution degradation and the MO degradation rate (K) of these as-formed nanocomposites was in an order: TiO2/CdS/C60 > TiO2/C60 > TiO2 > TiO2/CdS. In addition, Lian, Xu, Wang, Zhang, Xiao, Li and Li [84] successfully fabricated C60 decorated TiO2/CdS mesoporous photocatalyst via an evaporation combined with ion-exchanged method. It is noteworthy that the BET of the TiO2/CdS/C60 photocatalyst was actually lower than that of the TiO2/CdS composite, which resulted from the fact that the C60 was inset into the pore of this mesoporous composite. Compared with CdS/TiO2, the TiO2/CdS/C60 presented stronger visible light adsorption, lower recombination of photogenerated hole-electron pairs and higher photocurrent density, thus resulting in highly effectively photocatalytic ability for H2 production (Figure 4a–c). In Na2S-Na2SO3 reaction solution, the H2 generation rate of the optimal 0.5 wt % TiO2/CdS/C60 photocatalyst was 6.03µmol h1 g−1 with 2.0% quantum efficiency (QE) under visible light, which was obviously higher than the rate of TiO2/CdS (0.71 µmol h−1 g−1). As concluded in this study, C60 could enhance the light adsorption and facilitate the separation of photogenerated hole-electron pairs, as well as serve as H2 generation site for adsorbing and reducing H⁺ ions. The electron transfer route and reaction mechanism are presented in Figure 4d. Under visible light illumination, electrons in the VB of CdS are excited into the CB firstly. Then the excited electrons in the CB of CdS rapidly transfer into the CB of TiO2, because the conduction band potential of the former is more negative than that of the later. Finally, the electrons in the CB of TiO2 transfer to C60, which provide reaction sites for reducing H⁺ to H2. Meanwhile, the leaving holes in the VB of the CdS are consumed by S2− and SO3 2− to facilitate H2 generation efficiency. Moreover, Chai, Peng, Zhang, Mao, Li and Zhang [85] developed a TiO2-C60-dCNTs photocatalyst, which was reported to enhance the photocatalytic H2 production under UV light illumination. At a 5 wt % loading amount of C60, it exhibited the highest H2 production rate of 651 µmol h−1, which is 2.9 times that of bare TiO2.
Fullerenol (C60(OH)x), also called polyhydroxyfullerene (PHF), is a water-soluble fullerene derivative [99,100]. Typically, PHF could be prepared using fullerene via acid hydrolysis or alkali hydrolysis method [101,102,103]. In the earlier time, Krishna and his co-workers found that the addition of PHF in solution could elevate the photocatalytic activity of TiO2 under UV light illumination [104]. The reaction solution with PHF + TiO2 showed 2.6 times faster of photocatalytic organic dye degradation and 1.9 times faster of Escherichia coli inactivation than that of solution with TiO2 alone. While the hydroxylated fullerene (PHF) changes the electronic properties and decreases the electron affinity of fullerene, further studies were conducted by his group to explore the mechanisms of PHF to enhance the photocatalytic activity of TiO2 [105]. It was proposed that PHF covers onto the surface of TiO2 by electrostatic interactions in solution. The electron paramagnetic resonance (EPR) results showed that higher production rate of •OH was achieved under UV light after addition of PHF in solution, which contributed to enhancement of TiO2 photocatalytic activity. However, PHF alone in solution did not generate •OH under UV light, which suggested that synergistic effects come into being between PHF and TiO2. A hypothesis was proposed that PHF can scavenge the photo-generated electrons from TiO2 and meanwhile the synergistic effects of PHF and TiO2 can induce more •OH generation for enhancing the photodegradation activity. Furthermore, Park, et al. [106] proposed a new approach of CT in PHF/TiO2 system under visible light named as “surface-complex CT” procedure, which had not yet been proposed in TiO2/C60 system before. Note that fullerol has numerous hydroxyl groups which may link to the surface of TiO2 through the CT-complex route (Equation (4)). The photocurrents (Iph) of the PHF/TiO2-coated electrodes were examined, confirming that the transfer orientation of photogenerated electrons was from PHF to TiO2. In such surface-complex CT procedure, PHF serves as a photosensitizer in which electrons could be excited into CB of TiO2 under visible light irradiation, hence elevating the photocatalytic efficiency of TiO2. The reaction mechanism of radical generation is presented in Equations (5)−(8). Similar CT situations have been proposed in benzene/TiO2 system and even polycyclic aromatic hydrocarbons (PAH) physical-adsorbed TiO2 system as well [107,108].
C 60 ( OH ) x + Ti OH Ti O C 60 ( OH ) x 1 + H 2 O
Fullerol / TiO 2 + h v ( λ > 420   nm ) ( fullerol + ) / TiO 2 ( e cb )
( fullerol + ) / TiO 2 ( e cb ) fullerol / TiO 2
Fullerol / TiO 2 ( e cb ) TiO 2 / ( fullerol )
( fullerol + ) / TiO 2 + 0.5 H 2 O fullerol / TiO 2 + H + + 0.25 O 2
Bai, Krishna, Wang, Moudgil and Koopman [80] assembled a PHF/TiO2 nanocomposite by a physically mixing method in aqueous suspension and then coated the as-prepared sample onto grout substrate to examine its photocatalytic activity. The nanocomposite coating at a TiO2/PHF ratio of 0.01 exhibited the best photocatalytic efficiency under UV light irradiation. Accordingly, the 0.01 TiO2/PHF photocatalyst coating exhibited 2 times higher of Procion red MX-5B photocatalytic degradation efficiency and 3 times higher of photocatalytic spores of Aspergillus niger inactivation than these of bare TiO2 coating. Similarly, Hamandi, Berhault, Dappozze, Guillard and Kochkar [59] fabricated TiO2/PHF nanotubes using PHF and TiO2 nanotubes via wetness impregnation together with heat treated at 400 °C Under UV light illumination, the optimum 1% TiO2/PHF nanotubes showed a rate constant values (Kexp) of 94.7 µmolL−1 min1 for photocatalytic degradation towards formic acid, while TiO2 nanotubes alone exhibited the Kexp of 72.6 µmolL−1 min−1. Moreover, Lim, Monllor-Satoca, Jang, Lee and Choi [81] developed a Nb-TiO2/fullerol nanocomposite, which proved an elevated visible-light-driven photocatalytic performance. In brief, Nb-doped TiO2 was fabricated by a sol-gel method then the Nb-TiO2 was dispersed into fullerol solution buffered at pH 3 with HClO4. After stirring for 3 h, the filtered solids were dried at 80 °C to acquire brownish particles designated as Nb-TiO2/fullerol. The Nb-TiO2/fullerol showed more effectively photocatalytic performance for the reduction of Cr (VI), oxidation of iodide and degradation of 4-chlorophenol than naked TiO2, Nb−TiO2 and TiO2/fullerol under visible light. These results indicated that the synergistic effects between fullerol and Nb improved the photocatalytic activity of TiO2. It was proved that Nb doping induced vacancies of TiO2 by ionic substitution of Nb5+ in Ti4+ position, which could suppress the photoinduced hole-electron pairs recombination by trapping electrons. Notably, the fullerol significantly enhanced the visible light absorption of Nb-TiO2 through a surface-complex CT mechanism. Under visible light irradiation, electrons will be excited from HOMO of fullerol to CB of TiO2 and then from CB to vacancies, which effectively enhances the charge transport and prolongs the lifetime of photoinduced carriers. Another advantage was proposed that the Nb-TiO2/fullerol showed more highly photochemical stability over typical dye-sensitized-TiO2.

4.2. Metal Oxides (Except TiO2)/Fullerene Photocatalyst

In addition to TiO2, other metal oxides have also been promising materials in photocatalytic application [109,110,111]. Fullerene (C60 and C70) has some advantages to enhance the photocatalytic efficiency of these metal oxides, such as enhancing the light absorption and inhibiting recombination of photogenerated hole-electron pairs. Accordingly, a number of metal-oxide/fullerene photocatalysts have been successfully synthesized and extensively applied in photocatalytic pollutant degradation and H2 evolution via water splitting, such as ZnO/C60 (C70), WO3/C60 and SnO2/C60 [25,112].
Similar to TiO2, ZnO is an alternative photocatalyst with a band gap of 3.3 eV [113]. Generally, the absorption edge of pristine ZnO locates the near UV region, which usually restricts its photocatalytic efficiency. Meanwhile, the susceptibility to photocorrosion is also another barrier of ZnO for satisfactory photocatalytic performance. Fu, Xu, Zhu and Zhu [70] successfully prepared a C60 hybridized ZnO nanocomposite by a simple absorption method, and the sample with 1.5 wt % C60 exhibited the best photocatalytic sufficiency in MB degradation. The 1.5 wt % ZnO/C60 composite showed 95% photocatalytic degradation sufficiency towards MB under UV light, which was 3-times as high as that of bare ZnO. In such system, the elevated performance was ascribed to the improved light adsorption and a higher separation efficiency of photoinduced hole-electron pairs. During the photocatalysis process, the photogeneration holes could easily react with surface oxygen atom, leading to fast decline of photocatalytic activity of ZnO. When C60 was covered on ZnO, the activity of surface oxygen atoms was effectively reduced so that more holes could participate in photocatalytic reaction. Furthermore, the photocorrosion experiment indicated that the C60-hybridized ZnO nanocomposite did not show obviously decline of photocatalytic sufficiency even after illumination under UV light for 50 h, which was highly superior in stabilization than bare ZnO. Hence, the introduction of C60 effectually suppress photocorrosion of ZnO. Similarly, Hong, et al. [114] successfully prepared a ZnO/C70 nanocomposite via a heat treatment method, which exhibited superior photocatalytic degradation of organic dyes.
Recently, Tahir, Nabi, Rafique and Khalid [53] proposed the elevated photocatalytic efficiency of WO3/C60 nanocomposite for dye degradation and H2 evolution. The optimized 4 wt % WO3/C60 sample showed the best photodegradation ability and the degradation efficiency in MB, RhB and MO under visible light illumination was 93%, 92% and 91%, respectively. Meanwhile, the H2 evolution rate of the 4 wt % WO3/C60 was 2-times higher than that of bare WO3. After coupling with C60, the band gap of WO3/C60 nanocomposites were lower than that of bare WO3, which could excite more electrons of semiconductor WO3 from VB to CB. The BET surface area of these composites was also significantly increased, which could enhance the adsorption reaction. Based on the aforementioned study, Shahzad, Tahir and Sagir [87] constructed a novel heterogeneous photocatalyst WO3/[email protected]3B/Ni(OH)2 for H2 production. As a co-catalyst, Ni3B/Ni(OH)2 was loaded onto WO3/fullerene thin film by a facile photo-deposition technique. The optimal WO3/[email protected]%Ni3B/Ni(OH)2 presented an outstanding photocatalytic efficiency in H2 generation, reaching 1578µmol h−1 g1. In this system, it was proposed that three factors mainly contributed to the superior performance, including inhibition for recombination of photogeneration hole-electron pairs, more active sites for photocatalytic reaction and synergistic effect between nanocomposite and co-catalyst. Even earlier, a ternary photocatalyst WO3/C60/TiO2 was successfully prepared via a sol-gel method. Its photocatalytic performance in MO degradation was higher than that of WO3/C60 or TiO2/C60, which means these three materials synergistically enhance the photocatalytic activity [78].
In addition, Song, Zhang, Zeng, Wang, Ali and Zeng [83] fabricated a series C60 modified Fe2O3 polymorphs (α-, γ- and β-Fe2O3) photocatalysts via a simple adsorption method. These as-prepared samples showed superior photocatalytic efficiency in H2 production and even extremely outstanding effects were observed in the presence of fluorescein. Under visible light irradiation, the photocatalytic capacity was in the order: 1C60/β-Fe2O3 > 1C60/γ-Fe2O3> γ-Fe2O3 > 1C60/α-Fe2O3> β-Fe2O3 > g-C3N4 > α-Fe2O3. Behera, Mansingh, Das and Parida [71] proposed a ZnFe2O4-fullerene photocatalyst for norfloxacin decomposition and Cr (VI) reduction, wherein fullerene introducing significantly improved the photocatalytic capacity of ZnFe2O4. Moreover, Song, Huo, Liao, Zeng, Qin and Zeng [82] successfully prepared a novel photocatalyst Cr2-xFexO3/C60 via a simple adsorption method. In this study, α-Fe2O3 (~2.2eV) and Cr2O3 (~3.4eV) were integrated through a sol-gel method in order to construct Cr2-xFexO3 with a suitable band gap for H2 generation. While poor electron conducting ability limited its further application, the introducing of C60 was an effective way. The optimal 3%C60/Cr1.3Fe0.7O3 sample presented the H2 generation rate of 220.5 µmol h−1 g−1, which was about 2-times of the bare Cr1.3Fe0.7O3 composite.

4.3. Metal Sulfide/Fullerene Nanocomposites

Nowadays, metal sulfide semiconductors have attracted extensive attentions in photocatalytic application due to their distinctive optical-electrical characteristic [115,116,117]. CdS is an appealing photocatalyst with narrow bandgap (2.2~2.4 eV) exhibiting superior visible-light respond [118]. While fast recombination of hole-electron pairs and photocorrosion effect are the two main obstacles of naked CdS, which inhibits its photocatalytic efficiency. Coupling with fullerene was proved to be an effective way to boost the photocatalytic performance of CdS. Accordingly, Cai, Hu, Zhang, Li and Shen [43] successfully assembled a CdS/C60 nanocomposite via one-pot hydrothermal synthesis. The as-prepared samples showed better separation efficiency of photoinduced hole-electron pairs and higher photocurrent density than pure CdS (Figure 5a,b). Thus, the improvement of the aforementioned features contributed to a highly photocatalytic activity over CdS/C60 nanocomposite. The optimal H2 production rate of 0.4 wt % CdS/C60 was 1.73 mmol h−1 g−1 under visible light illumination, which was 2.3-times higher than that of naked CdS (Figure 5c). Its photocatalytic degradation efficiency towards RhB achieved 97% in 40 min (Figure 5d). Furthermore, the photostability of CdS was significantly boosted after CdS combining with C60, and 97.8% of RhB degradation efficiency actually retained after three recycles (Figure 5e). In order to estimate the stability of CdS/C60, the released Cd2+ concentration was determined in remaining solution after three cycles for RhB degradation (Figure 5f). The Cd2+ concentration was 381.3µg/L in solution with naked CdS while it was 51.9µg/L in solution with 0.4 wt %CdS/C60 nanomaterial, in which the former was 7.3 times of the later. The results above indicated that C60 could effectively inhibit the photocorrosion and boost the stability of CdS. Furthermore, Meng, Peng, Zhu, Oh and Zhang [56] assembled a novel ternary CdS/TiO2/C60 photocatalyst via a sol-gel method. The introduction of C60 definitely induced 56% increasement of the BET surface of the CdS/TiO2 composite, which could enhance the adsorption effect. Under the same condition, the MO degradation rate (K) of these nanocomposites was in an order: CdS/TiO2/C60 > TiO2/C60 > TiO2 > CdS/TiO2. This meant the CdS/TiO2/C60 composite obtained superior photocatalytic capacity owing to the synergistic reaction of C60, TiO2 and CdS. It was concluded in this study that the synergistic effects were as follows: (1) C60 could increase the quantum efficiency and charge transfer, as well as enhance the adsorption effect of the ternary photocatalyst; (2) Combining CdS with TiO2 endows the photocatalyst with a suitable bandgap for visible-light respond and a more effective electron transfer route for generating more •OH and •O2.
In addition, Meng and co-workers assembled CoS/C60 and AgS/C60 nanocomposites for pollutant decomposition [52,119]. Superior photocatalytic efficiency was obtained in these photocatalysts after the introduction of C60, since C60 is an energy sensitizer that could improve the quantum efficiency and boost charge transfer efficiency. More recently, Guan, Wu, Jiang, Zhu, Guan, Lei, Du, Zeng and Yang [54] fabricated a MoS2/C60 heterostructure photocatalyst via a ball milling method. The method does not need solvent to dissolve MoS2 and C60 and can significantly increase the BET surface of product. In this study, it was the first time to propose that a van der Waals heterostructure formed between MoS2 and C60 through ball milling, detailly wherein C60 nanoparticles bounded onto the edge of the exfoliated MoS2 nanosheet by non-covalent bond. Noteworthily, the CB minimum of MoS2/C60 was more negative than that of ball-milled MoS2 and the VB maximum of the former was more positive than that of the later. Thus, the as-prepared MoS2/C60 photocatalyst featured more suitable band gap for elevating the H2 evolution. Under visible light irradiation, the optimal 2.8 wt % MoS2/C60 sample exhibited the photocatalytic H2 production rate of 6.89 mmol h−1 g−1 in the presence of EY as a photosensitizer, which was 9.5 times higher than that of ball-milled MoS2 without C60.

4.4. Bismuth-Based Semiconductor/Fullerene Composites

Bismuth-based semiconductors have been proven promising materials for photocatalytic application, including BiOX (X = Br, Cl and I), Bi2WO6, BiVO4, Bi2MoO6, and so on [2,120,121]. Considerable research efforts have been devoted to couple these bismuth-based semiconductors with fullerene (C60 or C70) and enhanced photocatalytic performance could be obtained. For example, Zhu, Xu, Fu, Zhao and Zhu [40] successfully prepared C60 modified Bi2WO6 photocatalyst via a simple absorbing process, and 1.25 wt % Bi2WO6/C60 displayed 5.0-times the photocatalytic degradation activity towards MB with respect to unmodified Bi2WO6. Similarly, Ma, Zhong, Li, Wang and Peng [39] fabricated C70 modified BiOCl by an in-situ preparation procedure and superior photocatalytic performance was observed. Under solar irradiation for 30 min, 49.7% of RhB was degraded over pure BiOCl while 99.8% of RhB could be degraded over 1 wt % BiOCl/C70. In addition, Li, Jiang, Li, Lian, Xiao, Zhu, Zhang and Li [73] successfully developed Bi2TiO4F2/C60 photocatalyst via a solvothermal method, which was a hierarchical microsphere structure. The introduction of C60 can increase the photocurrent of the as-prepared sample, resulting from more efficient mobility efficiency of the charge carriers (Figure 6a). Owing to strong combining and heterojunction formation, the Bi2TiO4F2/C60 nanocomposite showed obviously elevated photocatalytic capacity for degrading RhB relative to bare Bi2TiO4F2 under visible light irradiation (Figure 6b). Meanwhile, the photocatalyst exhibited excellent stabilization as well and highly photocatalytic efficiency of RhB degradation (≈ 80%) was maintained even after eight circles (Figure 6c). The photocatalytic mechanisms of Bi2TiO4/C60 nanocomposite are described in Figure 6d. Apart from organic pollutant, bromate (BrO3) also exhibits biotoxicity to aquatic organisms and human since its properties non-biodegradation and accumulation. A strategy for controlling BrO3− pollution is to reduce it to Br which is naturally present in surface water bodies. Therefore, Zhao, Liu, Shen and Qu [46] studied the photocatalytic performance of Bi2MoO6/C60 for removal BrO3− under visible light. After modification with C60, Bi2MoO6/C60 exhibited sharply increase in photocatalytic reduction of BrO3−, attributed to the enhanced separation rate of photogenerated electron-hole pairs.

4.5. Carbon Nitride/Fullerene Composites

Graphitic carbon nitride (g-C3N4) is an attractive metal-free photocatalyst, which was developed by Wang et al. in 2009 [122]. The pristine g-C3N4 features a medium band gap (2.5~2.7 eV) with good visible light response [123]. Currently, this effective organo-photocatalyst has been widely used for pollutant degradation, water splitting and CO2 reduction [124,125]. However, pristine g-C3N4 exhibits insufficient solar absorption and rapid recombination of photogenerated carriers, which limits its photocatalytic efficiency. It has been proven that coupling g-C3N4 with fullerene is an effective way to enhance the photocatalytic sufficiency in pollutant degradation and H2 evolution. Recently, a series of g-C3N4/fullerene nanocomposites have been fabricated and they showed elevated photocatalytic efficiency.
Chai, Liao, Song and Zhou [45] prepared g-C3N4/C60 nanocomposites via a simple adsorption method. After C60 introduction, g-C3N4/C60 nanocomposites enhanced the visible light absorption without changing the absorption edge of g-C3N4, as well as lowered the recombination of photogenerated hole-electron pairs. The 1 wt % C3N4/C60 showed the highest photodegradation performance towards RhB, which could reach 97% degradation efficiency under visible light after 60 min. The reaction process could be proposed as follows (Equations (9)–(12)):
C 60 / C 3 N 4 h v   C 60 ( e ) / C 3 N 4 ( h + )
C 60 ( e ) + O 2 C 60 + O 2
O 2 + 2 e + 2 H + OH + OH
RhB + h + ( OH , O 2 ) products
Bai, Wang, Wang, Yao and Zhu [35] introduced C60 into g-C3N4 matric via thermal treatment of C60 and dicyandiamide mixture at 550 °C and the obtained nanocomposites exhibited higher photooxidation degradation efficiency towards phenol and MB. Relative to physical blend, this thermal treatment gave rise to strong interface interaction between g-C3N4 and C60. The g-C3N4/C60 nanocomposite exhibited higher specific surface area than pristine g-C3N4, leading to more active sites for catalytic reaction. The photocurrent value of g-C3N4/C60 is 4.0-times that of g-C3N4, which was highly responsible for enhancing the photocatalytic activity of pristine g-C3N4. Moreover, the introduction of C60 decreased the band gap of C3N4, wherein the value of g-C3N4 and g-C3N4/C60 were severally 2.70 eV and 2.58 eV, respectively. The calculation results showed that the valence band maximum (VBM) of C3N4/C60 is 0.17V lower than that of g-C3N4, which meant a stronger oxidizing capacity. Under visible light, the degradation ability of g-C3N4/C60 towards phenol and MB were 2.9- and 3.2-times as high as that of pristine g-C3N4, respectively. In addition, a series of C3N4/fullerene (C60, C70) photocatalysts were prepared by Ouyang, et al. [126] via a hydrothermal method for disinfection of bacterial pathogens under visible light irradiation. Regarding disinfection of E. coli O157:H7, both C3N4/C60 and C3N4/C70 hybrids showed stronger bacterial inactivation than pristine C3N4 after 4 h irradiation, and the C3N4/C70 exhibited the best performance. Note that both •O2 and •OH were identified as radical species to destruct bacterial cell in the solution under the visible light irradiation.
Coupling g-C3N4 with C60 could elevate the photocatalytic ability to H2 generation as well. For instance, Chen, Chen, Guan, Zhen, Sun, Du, Lu and Yang [55] successfully synthesized a covalent bonding g-C3N4/C60 nanocomposite via ball milling with LiOH as catalyst, which was the first time using this method for fabricating semiconductor/C60 nanocomposite. As depicted in XRD image, the lattice structure of g-C3N4 nanomaterial was changed after the attachment of C60 component (Figure 7a). It was proven that the covalent bonds were formed in the C3N4/C60 nanocomposite and a new peak at 399.5 eV was detected in XPS spectra, which was ascribed to N-C60 bond (Figure 7b). In this study, a new viewpoint was proposed that C60 forms covalent bond with g-C3N4 by a four-membered ring of azetidine. However, g-C3N4/C60 alone hardly exhibited the photocatalytic capacity in H2 evolution, thus additional photosensitizer was necessary. Under visible light, the H2 generation rate of g-C3N4/C60 was 266 µmol h−1g−1 using EY as a photosensitizer, which was 4.0 times higher than that of g-C3N4 in the same condition (Figure 7c). As depicted in Figure 7d, the mechanisms of g-C3N4/C60 nanocomposite are described for photocatalytic H2 generation. Recently, a novel g-C3N4/graphene/C60 composite was successfully prepared and significant enhancement for H2 evolution ability of the photocatalyst was observed [19]. In the presence of Pt (cocatalyst) and triethanolamine (sacrificial agent), the H2 evolution rate of the g-C3N4/graphene/C60 was 5449.5µmol g−1 within 10 h, which was 50.4 and 4.24 times that of g-C3N4/graphene and g-C3N4/C60, respectively. It means that C60 and graphene mutually reinforced synergy in H2 generation of g-C3N4, owing to high conductivity of graphene and excellent electron-attracting capacity of C60. Meanwhile, the quantum yield of g-C3N4/graphene/C60 reached 7.2% within 72 h.

4.6. Other Semiconductor/Fullerene Photocatalysts

Other semiconductors have also been coupled with fullerene to boost the photocatalytic activity. For example, Dai, Yao, Liu, Mohamed, Chen and Huang [50] successfully fabricated a PbMoO4-C60 photocatalyst via a hydrothermal method. After introduction of C60, no obvious change was visible in lattice structure of PbMoO4, but defects were observed on the surface of PbMoO4 (Figure 8a,b), which could be owed to the decreased crystallinity. As depicted in energy dispersive spectrometry (EDS), a great deal of C element was evenly dispersed on the surface of PbMoO4-C60 nanocomposite, which was regarded as a layer coating of C60 moiety (Figure 8c,d). Upon the attachment of the C60 moiety, the PbMoO4-C60 composite displayed obvious enhancement of both UV and visible light absorption (Figure 8e). Meanwhile, the Eg of 5.0 wt % PbMoO4-C60 (3.08 eV) was narrower than that of pure PbMoO4 (2.93 eV) (Figure 8f). Therefore, the improvement of optical features and energy band structure contributed to highly photocatalytic efficiency. Song, Yang, Chen and Zhang [72] prepared Ag3PO4/C60 photocatalyst via a simple chemical precipitation method. The photodegradation efficiency of MO achieved 93.5% within 8 min of visible light illumination. It is noteworthy that the introduction of C60 significantly enhanced the stabilization of Ag3PO4 which was usually susceptible to photo-corrosion. Additionally, some organic semiconductor nanoparticles composing of fullerene exhibited superior photocatalytic performance. For example, Huo and Zeng [86] successfully fabricated a triphenylamine functionalized bithiazole metal complex hybridized C60 photocatalyst. Under visible light irradiation, the photocatalytic H2 evolution of the as-prepared photocatalyst showed approximately 4–6-times higher than that of the pristine complex without fullerene. In this photocatalytic system, the organic metal nanocomposite worked as two roles which were both a photosensitizer and a photocatalyst. Additionally, Zhang, et al. [127] prepared an organic photocatalyst of fullerene hydrolyzed aluminum phthalocyanine chloride (AlPc/C60) by a reprecipitation method. The photocatalyst showed superior photooxidation degradation of various organic compounds (including N-methyl-2-pyrrolidone (NMP), methanal, and 2-mercaptoethanol). Note that the AlPc/C60 exhibited highly efficiency in complete mineralization towards these organic materials, leading to effective CO2 generation in reaction solution under visible light irradiation. NMP mineralization experiment was tested in a closed cylindrical reactor containing 10 vol% substrate, wherein the CO2 generation amount in AlPc/C60 reacting solution reached 3.7 × 10−7 mol after 24 h irradiation, which was 2.9-times higher than that of the corresponding C60 + AlPc mechanical mixture in solution. It was proposed that this novel photocatalyst based on a biphase structure and features p/n junction-like characteristics.

4.7. Discussions and Conclusions for Photocatalytic Applications of Fullerene/Semiconductor Photocatalysts

Among fullerene-based photocatalysts, the TiO2/fullerene (C60 and C70) composites have been the most extensively investigated in photocatalytic applications in the past decades. They exhibit efficient performances in wastewater treatment, such as pollutant degradation and disinfection. The synthetic methods are facile and eco-friendly without complicated steps, generally including simple adsorption and hydrothermal synthesis. After fullerene is inserted into TiO2, it shows to be fairly helpful in enhancing the photocatalytic efficiency of TiO2. However, there is a small deficiency in these materials, namely insufficient utilization of light energy. In other words, they exhibit excellent absorption of UV light but moderate absorption of visible light, while UV irradiation only accounts for 4% in solar irradiation. Besides, metal sulfide/fullerene nanocomposites are an appealing class of photocatalysts for not only decontamination but water splitting for H2 generation. They exhibit efficient absorption of visible light together with a moderate stability, such as CdS/C60, MoS2 and CdS/TiO2/C60. Compared with the responding pure metal sulfide, they perform significantly boosted efficiency, especially towards H2 generation. As to Bi-based semiconductor/fullerene photocatalysts, they appear to only be helpful for pollutant degradation but have not displayed effective capacity for photocatalytic H2 generation. There is no doubt that g-C3N4 has always been one of the hot nanomaterials in photocatalytic area since advent, so g-C3N4/fullerene photocatalysts are promising options for further photocatalysis. The facile synthetic method makes them attractive materials for photocatalytic applications, such as simple thermal treatment and balling mill. Additionally, it is easy to achieve more intensively oxidation or reduction capacity with tunable bandgap of g-C3N4.
To sum up, three crucial characteristics of photocatalysts are needed to be considered for wastewater treatment, such as high-efficiency for removing pollutant, stability in duration and nontoxicity to the environment and humans, respectively. In order to convincingly evaluate a photocatalyst, it is required to concern various properties comprehensively, such as optical absorption, energy band, photocatalytic efficiency, stability, cost and so on. As we all know, photocatalytic applications are currently researched in the laboratory, which seldom involves the time consumption of process and economic efficiency. Future work is imperative to focus on these aspects.

5. Fullerene/Support (Non-Semiconductor) Photocatalysts for Wastewater Treatment

In addition to fullerene/semiconductor photocatalysts, a series of novel fullerene/solid-support photocatalysts have been developed for wastewater treatment. It is well established that pristine fullerene is extremely insoluble in water (solubility of C60 in water < 10−9 mg/L), but could dissolve in nonpolar organic solvent, such as toluene and 1,2-dichlorobenzen [128,129]. It is worthwhile mentioning that fullerene solution could induce photochemical reactive oxygen species (ROS) generation via two pathways which were defined as type Ⅰ pathway (Equation (13)) and type Ⅱ pathway (Equation (14)), taking C60 as an example as follows [22]. For example, single oxygen 1O2 can be produced in fullerene-toluene solution (pathway Ⅱ), and O2−• and •OH can be generated in solvent in the present of electron donors such as EDTA and NADH (pathway Ⅰ) under UV light illumination [130,131]. While easily aggregation of pristine fullerene in water impedes ROS production owing to self-quenching mechanisms within the aggregates [132,133]. It has been proven that coupling fullerene with hydrophilic functional groups (namely fullerene derivatives) is a helpful strategy to dissolve fullerene in water together with superior ROS generation, such as polyhydroxyl-fullerene, amine-fullerene and other cationic-fullerenes [134,135,136]. At the earlier time, these water-soluble fullerene derivatives were used as photosensitizers for photodynamic therapy, selective antimicrobial and photooxidation organic synthesis [27,137]. More recently, considerable research efforts have been devoted to wastewater treatment for fullerene-support photocatalysts, including photocatalytic pollutant degradation and disinfection in aqueous solution. Without support combination, aqueous fullerene (nC60) and fullerene derivatives in aqueous solution are easily decomposed due to photolysis and other external conditions, seriously lowering efficacy of C60 as a photocatalyst generating ROS [138,139]. The separation and reutilization are also the barriers of fullerene derivatives used as photocatalysts. Herein, immobilization of fullerene-derivatives on solid support could be a hopeful strategy to fabricate fullerene/solid-support photocatalyst.
C 60 1 h ν C 60 * 1 I S C C 60 * 3 O 2 3 O 2 1 C 60 1
C 60 1 h ν C 60 * 1 I S C C 60 * 3 e d o n o r C 60 E r e d = + 1.14 V
Lee, et al. [140] fabricated a series of aminoC60/silica photocatalysts by covalent-bond immobilization of aminoC60 on 3-(2-succinic anhydride) propyl functionalized silica gel. The synthesis route of the aminoC60/silica photocatalysts is presented in Figure 9. In this photocatalytic system, phosphate buffer was required for pollutant degradation and 1O2 generated by photochemical procedure was the dominating ROS for photocatalytic activity. The photochemical 1O2 generation ability of the as-prepared photocatalysts were estimated using furfuryl alcohol (FFA) as an indicator and immobilized aminoC60 samples exhibited remarkedly higher 1O2 generation than water-soluble aminoC60, among which tetrakis aminoC60/silica performed the best (Figure 10a). Accordingly, these aminoC60/silica photocatalysts boosted the photocatalytic oxidation degradation towards pharmaceutical pollutants (including ranitidine and cimetidine) as well as photocatalytic disinfection towards MS-2 bacteriophage upon visible light illumination in contrast to corresponding aminoC60 alone in aqueous solution. In this case, the immobilization method facilitated well dispersion of C60 onto the silica surface, so as to expose more active sites for ROS generation, resulting in enhancement of the photocatalytic efficiency. Additionally, the huge specific surface area of silica significantly enhanced the adsorption of pollutant to the surface of aminoC60/silica for promoting closer contact between 1O2 and the pollutant, because the travel distance of 1O2 in aqueous is really short within the diffusion length of ∼125 nm over one lifetime [141]. Note that the lifetime of 1O2 in water was only 3~4 µs which limits the catalytic performance, so immobilization of aminoC60 could increase the contact time between 1O2 and the pollutant from this point of view [142]. In order to further explore the performance of the tetrakis aminoC60/silica photocatalyst, a variety of emerging organic contaminants and endocrine disruptors were involved into photocatalytic degradation experiments [143]. The photodegradation rate of ranitidine and propranolol for amino silica/C60 were 13.987 ± 0.016 h−1 and 10.77 ± 0.019 h−1, which were respectively 31-fold and 75-fold faster than that for aimnoC60 alone. In particular, the silica/aminoC60 was quite effective in trimethoprim degradation while no degradation appeared in aminoC60 aqueous solution, which was also observed in a C60 aminofullerene-magnetite nanocomposite suspension solution [144]. Moreover, at alkaline conditions (pH 10), acetaminophen, bisphenol A, and 4-chlorophenol could also be effectively degraded over the silica/aminoC60 photocatalyst under fluorescent light irradiation. Figure 10b,c compares the photocatalytic efficiency of silica/aminoC60 with other semiconductor photocatalysts including TiO2, C-TiO2 and Pt/WO3. It is shown that silica/aminoC60 exhibits remarkedly higher 1O2 generation rate over TiO2 and C-TiO2 while it performs lower rate than Pt/WO3 under fluorescent light or visible light irradiation. Note that the silica/aminoC60 exhibits the best efficiency in pharmaceutical (RA and CM) degradation among these materials under visible light irradiation. Although these photoactive catalysts in the comparisons take effect owing to different ROS generation (e.g., primarily 1O2 upon aminoC60, •OH upon TiO2 and Pt/WO3), it is indicated that silica/aminoC60 has a potential for application as an alternative environmental photocatalyst.
There is no denying that aforementioned fullerene/solid photocatalysts are involved into complicated synthesis procedure with fullerene derivatives. Moor and Kim [145] used a simpler method to build solid supported C60 photocatalysts via a nucleophilic reaction of a terminal amine onto pristine C60′s cage, and through this method SiO2/C60 and polystyrene resin/C60 (PS/C60) were developed. The above two photocatalysts both showed higher 1O2 generation rate than nC60 (nanoscale aggregates) in aqueous solution under various illumination conditions, in which the SiO2/C60 was superior to PS/C60. As a photosensitization catalyst, SiO2/C60 showed effectively photocatalytic MS2 inactivation, which was ascribed to 1O2-mediated oxidization damage effect. In addition, Moor, Valle, Li and Kim [91] successfully fabricated a MCM-41/C70 composite by the same nucleophilic reaction and it was the first time to use C70-solid support photocatalyst for wastewater treatment (Figure 11a). Within photoinactivation experiment towards MS2, the MCM-41/C70 performed obviously higher efficiency than N-TiO2 nanocomposite, which efficiently induced •OH production in aqueous solution for microbial inactivation (Figure 11b,c). It was confirmed that the as-prepared novel MCM-41/C70 photocatalyst exhibited efficient photodegradation ability to several pharmaceuticals and personal care products (PPCP), including bisphenol A, 17-α-ethynylestradiol and amoxicillin (Figure 11d,e).
The majority of photocatalysts researched for traditional azo-dye decomposition based upon semiconductor composites. Few studies involved into non-semiconducting materials, especially C60/solid support photocatalyst [146]. Whereas, Wakimoto, et al. [147] prepared a SiO2/C60 powder via a simple adsorption using pristine C60 and silica gel in toluene and it was important to highlight that a novel route for dye photodegradation was proposed for the C60/solid support photocatalyst. Unlike typically semiconductor photocatalysts, the SiO2/C60 composite exhibited effectively visible-light-driven photocatalytic degradation towards methyl orange in the presence ascorbic acid, while SiO2/C60 alone without ascorbic acid did not show degradation performance. In this case, ascorbic acid could protonate MO and transform it into quinoid form with strong electron-acceptability. It was proved that both 1O2 and O2•− species took part in the dye degradation. On one hand, C60 dispersed onto silica surface was excited to undergo the intersystem crossing from the single to triplet state for 1O2 generating, then the generated 1O2 could attack rich-electron quinoid structure to decompose MO. On the other hand, the electron transferred from ascorbic acid to the excited C60 to forming the C60 radical anion, followed by generation of O2•− via O2 receiving the electron from C60•−, wherein O2•− was an effective specie for dye degradation. It was also confirmed that methyl red could be decomposed by SiO2/C60 at the same conditions. Likewise, Kyriakopoulos, et al. [148] successfully fabricated a MCM-41/C60 photocatalyst via a dry impregnation method. Coupling C60 with MCM-41 significantly increased the BET of the as-prepared photocatalyst, thus effectively dispersing C60 clusters as well as strengthening its adsorption ability to pollutant. The optimum 3MCM-41/C60 (3 wt % C60) sample showed 74.9% decolorization efficiency in Orange G, which was markedly higher than that of C60 alone. This photocatalyst proved to be remarkably stable, wherein less than 5% photodegradation efficiency was lost after five cycles.
Fullerene-based solid photocatalysts could effectively prevent fullerene aggregations and enhance the photo-stabilization of fullerene alone as well as enhance the pollutant adsorption due to the introduced support, thus leading to increase the photocatalytic efficiency. In the meanwhile, this fullerene-based photocatalyst could perform selected oxidization of pollutant with 1O2 that can prevent natural organic matter (NOM) interference, which underline the potential of these materials for wastewater treatment in natural water. Therefore, fullerene-based support photocatalysts are promising materials for environmental applications and further effort will be required to fabricate novel photocatalysts of this type.

6. Conclusions and Perspectives

In summary, the essence of photocatalysis bases on the ROS generation in the presence of light resource irradiation. Fullerenes, including C60 and C70, have been extensively investigated in the photocatalytic application due to their unique optical and photochemical characteristics. Fullerene could be anchored on semiconductors to enhance their photocatalytic activity, and also supported on non-semiconductor solids to fabricate novel fullerene-based photocatalysts due to its self-photocatalytic features. In the present review, fullerene/semiconductor photocatalysts and fullerene-solid support photocatalysts are summarized for wastewater treatment (pollutant degradation, Cr(VI) reduction, disinfection etc.) and water splitting for H2 generation. A number of synthesis methods have been used to fabricate semiconductor/fullerene photocatalysts, including simple adsorption, hydrothermal synthesis, ball milling, sol-gel and so on. The semiconductors alone usually display limited photocatalytic performance, wherein the fast recombination of photoinduced hole-electron pairs and inefficient light energy utilization are the two main obstacles. Whereas, fullerene could availably enhance the photocatalytic efficiency of semiconductors by retarding the recombination of hole-electron pairs and increasing the light absorption (UV and visible light). In some cases, semiconductor/fullerene photocatalysts display better stabilization than semiconductors alone, and the introduced fullerene increases the BET of the semiconductor for enhancing the pollutant adsorption. The studies manifest that excess fullerene inhibits the photocatalytic ability due to the coverage effect towards excited sites. So, a suitable amount of fullerene is imperative for superior photocatalytic activity of semiconductor/fullerene photocatalysts. Plentiful semiconductors have been coupled with fullerene for wastewater treatment and water splitting, such as TiO2, ZnO, CdS and C3N4. The photocatalytic effect of these photocatalysts are presented and the involved mechanisms are discussed in detail in this review, including the reaction of ROS generation and the transfer route of electron. On the other hand, fullerene-solid support photocatalysts are also discussed in application for wastewater treatment, such as silica/C60, MCM-41/C70 and polysiloxane-supported fullerene photocatalyst. They display excellent photoinduced ROS (mainly 1O2) generation in aqueous solution after fullerene was dispersed onto the solid support, which is the direct factor contributing to the photocatalytic reaction. Meanwhile, they effectively enhance the photo-stabilization of fullerene alone as well as enhance the pollutant adsorption. It is noteworthy that these fullerene-based photocatalysts perform selected oxidization of the pollutant, wherein the photoinduced 1O2 could prevent natural organic matter (NOM) interference. So, it underlines the potential of these materials for wastewater treatment in natural water.
Although some encouraging properties have been achieved for fullerene-based photocatalysts, the development of fullerene-based photocatalysts still has remaining challenges. (1) The interface contact between the fullerene and semiconductor is not so intimate, leading to limiting the electron transport ability and photostability of semiconductor/fullerene photocatalysts. The majority of semiconductor/fullerene photocatalysts formed by simple adsorption and hydrothermal synthesis, while few studies confirmed the existence of covalent bond or other tight bond in them. (2) The photocatalytic mechanisms of fullerene/semiconductor photocatalysts are partly not clear. Some studies indicated that the electrons transfer from the semiconductor to the fullerene due to the strong electron-accepting ability of fullerene, while others deemed that the electrons transfer in the opposite direction. (3) Not enough research has been done on the novel fullerene/solid (non-semiconductor) photocatalysts, in which the selection of solid support is restricted to silica, MCM-41 and polysiloxane. (4) The majority of fullerene-based photocatalysts are investigated in the treatment of simulated wastewater with the artificial addition of a single pollutant, and actual industrial wastewater is rarely involved.
In our opinion, several directions are worthy of attention for fullerene-based photocatalysts in the future: (1) Innovative strategy should be developed to construct semiconductor/fullerene photocatalysts with efficient performance and high stability. (2) Further works should focus on mechanism studies of the semiconductor/fullerene composite, especially the electron-transfer path which is still in dispute. (3) More attention should be paid to fullerene derivatives, which are promising materials for developing novel fullerene-based photocatalysts. (4) The studying of fullerene-based photocatalysts on their actual performance in natural water, industrial wastewater and multi-polluted wastewater.

Author Contributions

Conceptualization, X.Y. and L.J.; writing—original draft preparation, S.Y.; writing—review and editing, T.X. and J.Z. All authors have read and agreed to the published version of the manuscript.

Funding

The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (No. 51739004, 21776066 and 71431006).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Pan, Y.; Yuan, X.; Jiang, L.; Yu, H.; Zhang, J.; Wang, H.; Guan, R.; Zeng, G. Recent advances in synthesis, modification and photocatalytic applications of micro/nano-structured zinc indium sulfide. Chem. Eng. J. 2018, 354, 407–431. [Google Scholar] [CrossRef]
  2. Yi, H.; Qin, L.; Huang, D.; Zeng, G.; Lai, C.; Liu, X.; Li, B.; Wang, H.; Zhou, C.; Huang, F.; et al. Nano-structured bismuth tungstate with controlled morphology: Fabrication, modification, environmental application and mechanism insight. Chem. Eng. J. 2019, 358, 480–496. [Google Scholar] [CrossRef]
  3. Fujishima, A.; Honda, K. Electrochemical Photolysis of Water at a Semiconductor Electrode. Nature 1972, 238, 37–38. [Google Scholar] [CrossRef]
  4. Smazna, D.; Rodrigues, J.; Shree, S.; Postica, V.; Neubueser, G.; Martins, A.F.; Ben Sedrine, N.; Jena, N.K.; Siebert, L.; Schuett, F.; et al. Buckminsterfullerene hybridized zinc oxide tetrapods: Defects and charge transfer induced optical and electrical response. Nanoscale 2018, 10, 10050–10062. [Google Scholar] [CrossRef]
  5. Zhang, W.; Wang, Y.; Wang, Z.; Zhong, Z.; Xu, R. Highly efficient and noble metal-free NiS/CdS photocatalysts for H2 evolution from lactic acid sacrificial solution under visible light. Chem. Commun. 2010, 46, 7631–7633. [Google Scholar] [CrossRef]
  6. Luo, C.-Y.; Huang, W.-Q.; Xu, L.; Yang, Y.-C.; Li, X.; Hu, W.; Peng, P.; Huang, G.-F. Enhanced photocatalytic performance of an Ag3PO4 photocatalyst via fullerene modification: First-principles study. Phys. Chem. Chem. Phys. 2016, 18, 2878–2886. [Google Scholar] [CrossRef]
  7. Obregón, S.; Caballero, A.; Colón, G. Hydrothermal synthesis of BiVO4: Structural and morphological influence on the photocatalytic activity. Appl. Catal. B 2012, 117, 59–66. [Google Scholar] [CrossRef]
  8. Yu, H.; Jiang, L.; Wang, H.; Huang, B.; Yuan, X.; Huang, J.; Zhang, J.; Zeng, G. Modulation of Bi2MoO6-Based Materials for Photocatalytic Water Splitting and Environmental Application: A Critical Review. Small 2019, 15, 1901008. [Google Scholar] [CrossRef] [PubMed]
  9. Wang, H.; Yuan, X.; Wu, Y.; Zeng, G.; Dong, H.; Chen, X.; Leng, L.; Wu, Z.; Peng, L. In situ synthesis of [email protected](Ti) core-shell microparticle for the removal of tetracycline from wastewater by integrated adsorption and visible-light-driven photocatalysis. Appl. Catal. B 2016, 186, 19–29. [Google Scholar] [CrossRef]
  10. Jiang, L.; Yuan, X.; Pan, Y.; Liang, J.; Zeng, G.; Wu, Z.; Wang, H. Doping of graphitic carbon nitride for photocatalysis: A reveiw. Appl. Catal. B 2017, 217, 388–406. [Google Scholar] [CrossRef]
  11. Xiang, Q.; Yu, J.; Jaroniec, M. Synergetic Effect of MoS2 and Graphene as Cocatalysts for Enhanced Photocatalytic H2 Production Activity of TiO2 Nanoparticles. J. Am. Chem. Soc. 2012, 134, 6575–6578. [Google Scholar] [CrossRef] [PubMed]
  12. Zong, X.; Han, J.; Ma, G.; Yan, H.; Wu, G.; Li, C. Photocatalytic H2 Evolution on CdS Loaded with WS2 as Cocatalyst under Visible Light Irradiation. J. Phys. Chem. C 2011, 115, 12202–12208. [Google Scholar] [CrossRef]
  13. Yeh, T.-F.; Cihlář, J.; Chang, C.-Y.; Cheng, C.; Teng, H. Roles of graphene oxide in photocatalytic water splitting. Mater. Today 2013, 16, 78–84. [Google Scholar] [CrossRef]
  14. Ge, J.; Zhang, Y.; Park, S.-J. Recent Advances in Carbonaceous Photocatalysts with Enhanced Photocatalytic Performances: A Mini Review. Materials 2019, 12, 1916. [Google Scholar] [CrossRef]
  15. Gangu, K.K.; Maddila, S.; Jonnalagadda, S.B. A review on novel composites of MWCNTs mediated semiconducting materials as photocatalysts in water treatment. Sci. Total Environ. 2019, 646, 1398–1412. [Google Scholar] [CrossRef] [PubMed]
  16. Luo, Y.; Heng, Y.; Dai, X.; Chen, W.; Li, J. Preparation and photocatalytic ability of highly defective carbon nanotubes. J. Solid State Chem. 2009, 182, 2521–2525. [Google Scholar] [CrossRef]
  17. Yeh, T.-F.; Syu, J.-M.; Cheng, C.; Chang, T.-H.; Teng, H. Graphite Oxide as a Photocatalyst for Hydrogen Production from Water. Adv. Funct. Mater. 2010, 20, 2255–2262. [Google Scholar] [CrossRef]
  18. Krishnamoorthy, K.; Mohan, R.; Kim, S.J. Graphene oxide as a photocatalytic material. Appl. Phys. Lett. 2011, 98, 244101. [Google Scholar] [CrossRef]
  19. Song, L.; Guo, C.; Li, T.; Zhang, S. C-60/graphene/g-C3N4 composite photocatalyst and mutually-reinforcing synergy to improve hydrogen production in splitting water under visible light radiation. Ceram. Int. 2017, 43, 7901–7907. [Google Scholar] [CrossRef]
  20. Li, Q.; Xu, L.; Luo, K.W.; Huang, W.Q.; Wang, L.L.; Li, X.F.; Huang, G.F.; Yu, Y.B. Insights into enhanced visible-light photocatalytic activity of C60 modified g-C3N4 hybrids: The role of nitrogen. Phys. Chem. Chem. Phys. 2016, 18, 33094–33102. [Google Scholar] [CrossRef]
  21. Kumar, I.; Sharma, R.; Kumar, R.; Kumar, R.; Sharma, U. C-70 Fullerene-Catalyzed Metal-Free Photocatalytic ipso-Hydroxylation of Aryl Boronic Acids: Synthesis of Phenols. Adv. Synth. Catal. 2018, 360, 2013–2019. [Google Scholar] [CrossRef]
  22. Yamakoshi, Y.; Umezawa, N.; Ryu, A.; Arakane, K.; Miyata, N.; Goda, Y.; Masumizu, T.; Nagano, T. Active Oxygen Species Generated from Photoexcited Fullerene (C60) as Potential Medicines:  O2-versus 1O2. J. Am. Chem. Soc. 2003, 125, 12803–12809. [Google Scholar] [CrossRef] [PubMed]
  23. Panahian, Y.; Arsalani, N.; Nasiri, R. Enhanced photo and sono-photo degradation of crystal violet dye in aqueous solution by 3D flower like F-TiO2(B)/fullerene under visible light. J. Photochem. Photobiol. A Chem. 2018, 365, 45–51. [Google Scholar] [CrossRef]
  24. Hu, Y.; Xie, X.; Wang, X.; Wang, Y.; Zeng, Y.; Pui, D.Y.H.; Sun, J. Visible-Light Upconversion Carbon Quantum Dots Decorated TiO2 for the Photodegradation of Flowing Gaseous Acetaldehyde. Appl. Surf. Sci. 2018, 440, 266–274. [Google Scholar] [CrossRef]
  25. Cho, B.H.; Lee, K.B.; Miyazawa, K.I.; Ko, W.B. Preparation of Fullerene (C-60) Nanowhisker-ZnO Nanocomposites by Heat Treatment and Photocatalytic Degradation of Methylene Blue. Asian J. Chem. 2013, 25, 8027–8030. [Google Scholar] [CrossRef]
  26. Panagiotou, G.D.; Tzirakis, M.D.; Vakros, J.; Loukatzikou, L.; Orfanopoulos, M.; Kordulis, C.; Lycourghiotis, A. Development of 60 fullerene supported on silica catalysts for the photo-oxidation of alkenes. Appl. Catal. A Gen. 2010, 372, 16–25. [Google Scholar] [CrossRef]
  27. Latassa, D.; Enger, O.; Thilgen, C.; Habicher, T.; Offermanns, H.; Diederich, F. Polysiloxane-supported fullerene derivative as a new heterogeneous sensitiser for the selective photooxidation of sulfides to sulfoxides by 1O2. J. Mater. Chem. 2002, 12, 1993–1995. [Google Scholar] [CrossRef]
  28. Manjon, F.; Santana-Magana, M.; Garcia-Fresnadillo, D.; Orellana, G. Are silicone-supported [C60]-fullerenes an alternative to Ru(II) polypyridyls for photodynamic solar water disinfection? Photochem. Photobiol. Sci. 2014, 13, 397–406. [Google Scholar] [CrossRef]
  29. Guan, G.; Ye, E.; You, M.; Li, Z. Hybridized 2D Nanomaterials Toward Highly Efficient Photocatalysis for Degrading Pollutants: Current Status and Future Perspectives. Small 2020, 16, 1907087. [Google Scholar] [CrossRef]
  30. Perovic, K.; Dela Rosa, F.M.; Kovacic, M.; Kusic, H.; Lavrencic Stangar, U.; Fresno, F.; Dionysiou, D.D.; Bozic, A.L. Recent Achievements in Development of TiO2-Based Composite Photocatalytic Materials for Solar Driven Water Purification and Water Splitting. Materials 2020, 13, 1338. [Google Scholar] [CrossRef]
  31. Xu, T.; Zhu, R.; Zhu, J.; Liang, X.; Zhu, G.; Liu, Y.; Xu, Y.; He, H. Fullerene modification of Ag3PO4 for the visible-light-driven degradation of acid red 18. RSC Adv. 2016, 6, 85962–85969. [Google Scholar] [CrossRef]
  32. Sepahvand, S.; Farhadi, S. Preparation and characterization of fullerene (C-60)-modified BiVO4/Fe3O4 nanocomposite by hydrothermal method and study of its visible light photocatalytic and catalytic activity. Fuller. Nanotub. Carbon Nanostruct. 2018, 26, 417–432. [Google Scholar] [CrossRef]
  33. Virovska, D.; Paneva, D.; Manolova, N.; Rashkov, I.; Karashanova, D. Photocatalytic self-cleaning poly(L-lactide) materials based on a hybrid between nanosized zinc oxide and expanded graphite or fullerene. Mater. Sci. Eng. C Mater. Biol. Appl. 2016, 60, 184–194. [Google Scholar] [CrossRef] [PubMed]
  34. Ding, S.-S.; Huang, W.-Q.; Zhou, B.-X.; Peng, P.; Hu, W.-Y.; Long, M.-Q.; Huang, G.-F. The mechanism of enhanced photocatalytic activity of SnO2 through fullerene modification. Curr. Appl. Phys. 2017, 17, 1547–1556. [Google Scholar] [CrossRef]
  35. Bai, X.; Wang, L.; Wang, Y.; Yao, W.; Zhu, Y. Enhanced oxidation ability of g-C3N4 photocatalyst via C60 modification. Appl. Catal. B 2014, 153, 262–270. [Google Scholar] [CrossRef]
  36. Meng, Z.-D.; Zhu, L.; Oh, W.-C. Preparation and high visible-light-induced photocatalytic activity of CdSe and CdSe-C-60 nanoparticles. J. Ind. Eng. Chem. 2012, 18, 2004–2009. [Google Scholar] [CrossRef]
  37. Luo, C.-Y.; Huang, W.-Q.; Hu, W.; Peng, P.; Huang, G.-F. Non-covalent functionalization of WS2 monolayer with small fullerenes: Tuning electronic properties and photoactivity. Dalton Trans. 2016, 45, 13383–13391. [Google Scholar] [CrossRef]
  38. Ju, L.; Wu, P.; Lai, X.; Yang, S.; Gong, B.; Chen, M.; Zhu, N. Synthesis and characterization of Fullerene modified ZnAlTi-LDO in photo-degradation of Bisphenol A under simulated visible light irradiation. Environ. Pollut. 2017, 228, 234–244. [Google Scholar] [CrossRef]
  39. Ma, D.; Zhong, J.; Li, J.; Wang, L.; Peng, R. Enhanced photocatalytic activity of BiOCl by C-70 modification and mechanism insight. Appl. Surf. Sci. 2018, 443, 497–505. [Google Scholar] [CrossRef]
  40. Zhu, S.; Xu, T.; Fu, H.; Zhao, J.; Zhu, Y. Synergetic effect of Bi2WO6 photocatalyst with C-60 and enhanced photoactivity under visible irradiation. Environ. Sci. Technol. 2007, 41, 6234–6239. [Google Scholar] [CrossRef]
  41. Aich, N.; Flora, J.; Saleh, N. Preparation and characterization of stable aqueous higher-order fullerenes. Nanotechnology 2012, 23, 55705. [Google Scholar] [CrossRef]
  42. Sampaio, M.J.; Bacsa, R.R.; Benyounes, A.; Axet, R.; Serp, P.; Silva, C.G.; Silva, A.M.T.; Faria, J.L. Synergistic effect between carbon nanomaterials and ZnO for photocatalytic water decontamination. J. Catal. 2015, 331, 172–180. [Google Scholar] [CrossRef]
  43. Cai, Q.; Hu, Z.; Zhang, Q.; Li, B.; Shen, Z. Fullerene (C-60)/CdS nanocomposite with enhanced photocatalytic activity and stability. Appl. Surf. Sci. 2017, 403, 151–158. [Google Scholar] [CrossRef]
  44. Prylutskyy, Y.I.; Petrenko, V.I.; Ivankov, O.I.; Kyzyma, O.A.; Bulavin, L.A.; Litsis, O.O.; Evstigneev, M.P.; Cherepanov, V.V.; Naumovets, A.G.; Ritter, U. On the Origin of C60 Fullerene Solubility in Aqueous Solution. Langmuir 2014, 30, 3967–3970. [Google Scholar] [CrossRef] [PubMed]
  45. Chai, B.; Liao, X.; Song, F.; Zhou, H. Fullerene modified C3N4 composites with enhanced photocatalytic activity under visible light irradiation. Dalton Trans. 2014, 43, 982–989. [Google Scholar] [CrossRef] [PubMed]
  46. Zhao, X.; Liu, H.; Shen, Y.; Qu, J. Photocatalytic reduction of bromate at C60 modified Bi2MoO6 under visible light irradiation. Appl. Catal. B 2011, 106, 63–68. [Google Scholar] [CrossRef]
  47. Zhang, L.; Wang, Y.; Xu, T.; Zhu, S.; Zhu, Y. Surface hybridization effect of C60 molecules on TiO2 and enhancement of the photocatalytic activity. J. Mol. Catal. A Chem. 2010, 331, 7–14. [Google Scholar] [CrossRef]
  48. Yu, J.; Ma, T.; Liu, G.; Cheng, B. Enhanced photocatalytic activity of bimodal mesoporous titania powders by C-60 modification. Dalton Trans. 2011, 40, 6635–6644. [Google Scholar] [CrossRef] [PubMed]
  49. Ouyang, K.; Dai, K.; Walker, S.L.; Huang, Q.; Yin, X.; Cai, P. Efficient Photocatalytic Disinfection of Escherichia coli O157:H7 using C-70-TiO2 Hybrid under Visible Light Irradiation. Sci. Rep. 2016, 6, 25702. [Google Scholar] [CrossRef]
  50. Dai, K.; Yao, Y.; Liu, H.; Mohamed, I.; Chen, H.; Huang, Q. Enhancing the photocatalytic activity of lead molybdate by modifying with fullerene. J. Mol. Catal. A Chem. 2013, 374, 111–117. [Google Scholar] [CrossRef]
  51. Lin, X.; Xi, Y.; Zhao, R.; Shi, J.; Yan, N. Construction of C-60-decorated SWCNTs (C-60-CNTs)/bismuth-based oxide ternary heterostructures with enhanced photocatalytic activity. RSC Adv. 2017, 7, 53847–53854. [Google Scholar] [CrossRef]
  52. Meng, Z.-D.; Zhu, L.; Ullah, K.; Ye, S.; Sun, Q.; Jang, W.K.; Oh, W.-C. Study of the photochemically generated of oxygen species by fullerene photosensitized CoS2 nanocompounds. Mater. Res. Bull. 2014, 49, 272–278. [Google Scholar] [CrossRef]
  53. Tahir, M.B.; Nabi, G.; Rafique, M.; Khalid, N.R. Role of fullerene to improve the WO3 performance for photocatalytic applications and hydrogen evolution. Int. J. Energy Res. 2018, 42, 4783–4789. [Google Scholar] [CrossRef]
  54. Guan, J.; Wu, J.; Jiang, D.; Zhu, X.; Guan, R.; Lei, X.; Du, P.; Zeng, H.; Yang, S. Hybridizing MoS2 and C-60 via a van der Waals heterostructure toward synergistically enhanced visible light photocatalytic hydrogen production activity. Int. J. Hydrog. Energy 2018, 43, 8698–8706. [Google Scholar] [CrossRef]
  55. Chen, X.; Chen, H.; Guan, J.; Zhen, J.; Sun, Z.; Du, P.; Lu, Y.; Yang, S. A facile mechanochemical route to a covalently bonded graphitic carbon nitride (g-C3N4) and fullerene hybrid toward enhanced visible light photocatalytic hydrogen production. Nanoscale 2017, 9, 5615–5623. [Google Scholar] [CrossRef]
  56. Meng, Z.-D.; Peng, M.-M.; Zhu, L.; Oh, W.-C.; Zhang, F.-J. Fullerene modification CdS/TiO2 to enhancement surface area and modification of photocatalytic activity under visible light. Appl. Catal. B Environ. 2012, 113, 141–149. [Google Scholar] [CrossRef]
  57. Li, J.; Ko, W.B. Facile Synthesis of MoS2-C60Nanocomposites and Their Application to Catalytic Reduction and Photocatalytic Degradation. Elastom. Compos. 2016, 51, 286–300. [Google Scholar] [CrossRef]
  58. Apostolopoulou, V.; Vakros, J.; Kordulis, C.; Lycourghiotis, A. Preparation and characterization of 60 fullerene nanoparticles supported on titania used as a photocatalyst. Colloids Surf. A Physicochem. Eng. Asp. 2009, 349, 189–194. [Google Scholar] [CrossRef]
  59. Hamandi, M.; Berhault, G.; Dappozze, F.; Guillard, C.; Kochkar, H. Titanium dioxide nanotubes/polyhydroxyfullerene composites for formic acid photodegradation. Appl. Surf. Sci. 2017, 412, 306–318. [Google Scholar] [CrossRef]
  60. Donar, Y.O.; Bilge, S.; Sinag, A.; Pliekhov, O. TiO2/Carbon Materials Derived from Hydrothermal Carbonization of Waste Biomass: A Highly Efficient, Low-Cost Visible-Light-Driven Photocatalyst. Chemcatchem 2018, 10, 1134–1139. [Google Scholar] [CrossRef]
  61. Mu, S.; Long, Y.; Kang, S.-Z.; Mu, J. Surface modification of TiO2 nanoparticles with a C60 derivative and enhanced photocatalytic activity for the reduction of aqueous Cr(VI) ions. Catal. Commun. 2010, 11, 741–744. [Google Scholar] [CrossRef]
  62. Zhao, Z.; An, H.; Lin, J.; Feng, M.; Murugadoss, V.; Ding, T.; Liu, H.; Shao, Q.; Mai, X.; Wang, N.; et al. Progress on the Photocatalytic Reduction Removal of Chromium Contamination. Chem. Rec. 2019, 19, 873–882. [Google Scholar] [CrossRef] [PubMed]
  63. Lü, X.-F.; Qian, H.; Mele, G.; De Riccardis, A.; Zhao, R.; Chen, J.; Wu, H.; Hu, N.-J. Impact of different TiO2 samples and porphyrin substituents on the photocatalytic performance of TiO2@copper porphyrin composites. Catal. Today 2017, 281, 45–52. [Google Scholar] [CrossRef]
  64. Hashimoto, K.; Irie, H.; Fujishima, A. TiO2 Photocatalysis: A Historical Overview and Future Prospects. Jpn. J. Appl. Phys. 2005, 44, 8269–8285. [Google Scholar] [CrossRef]
  65. Fujishima, A.; Zhang, X.; Tryk, D.A. TiO2 photocatalysis and related surface phenomena. Surf. Sci. Rep. 2008, 63, 515–582. [Google Scholar] [CrossRef]
  66. Youssef, Z.; Colombeau, L.; Yesmurzayeva, N.; Baros, F.; Vanderesse, R.; Hamieh, T.; Toufaily, J.; Frochot, C.; Roques-Carmes, T.; Acherar, S. Dye-sensitized nanoparticles for heterogeneous photocatalysis: Cases studies with TiO2, ZnO, fullerene and graphene for water purification. Dyes Pigm. 2018, 159, 49–71. [Google Scholar] [CrossRef]
  67. Oh, W.-C.; Jung, A.-R.; Ko, W.-B. Preparation of fullerene/TiO2 composite and its photocatalytic effect. J. Ind. Eng. Chem. 2007, 13, 1208–1214. [Google Scholar]
  68. Zhang, X.; Wang, Q.; Zou, L.-H.; You, J.-W. Facile fabrication of titanium dioxide/fullerene nanocomposite and its enhanced visible photocatalytic activity. J. Colloid Interface Sci. 2016, 466, 56–61. [Google Scholar] [CrossRef]
  69. Wang, S.; Liu, C.; Dai, K.; Cai, P.; Chen, H.; Yang, C.; Huang, Q. Fullerene C-70-TiO2 hybrids with enhanced photocatalytic activity under visible light irradiation. J. Mater. Chem. A 2015, 3, 21090–21098. [Google Scholar] [CrossRef]
  70. Fu, H.; Xu, T.; Zhu, S.; Zhu, Y. Photocorrosion Inhibition and Enhancement of Photocatalytic Activity for ZnO via Hybridization with C-60. Environ. Sci. Technol. 2008, 42, 8064–8069. [Google Scholar] [CrossRef]
  71. Behera, A.; Mansingh, S.; Das, K.K.; Parida, K. Synergistic ZnFe2O4-carbon allotropes nanocomposite photocatalyst for norfloxacin degradation and Cr (VI) reduction. J. Colloid Interface Sci. 2019, 544, 96–111. [Google Scholar] [CrossRef] [PubMed]
  72. Song, L.; Yang, J.; Chen, Q.; Zhang, S. Enhanced photocatalytic activity of Ag3PO4 via Fullerene C-60 modification. Appl. Organomet. Chem. 2018, 32, e4472. [Google Scholar] [CrossRef]
  73. Li, G.; Jiang, B.; Li, X.; Lian, Z.; Xiao, S.; Zhu, J.; Zhang, D.; Li, H. C-60/Bi2TiO4F2 Heterojunction Photocatalysts with Enhanced Visible-Light Activity for Environmental Remediation. ACS Appl. Mater. Interface 2013, 5, 7190–7197. [Google Scholar] [CrossRef] [PubMed]
  74. Sepahvand, S.; Farhadi, S. Fullerene-modified magnetic silver phosphate (Ag3PO4/Fe3O4/C-60) nanocomposites: Hydrothermal synthesis, characterization and study of photocatalytic, catalytic and antibacterial activities. RSC Adv. 2018, 8, 10124–10140. [Google Scholar] [CrossRef]
  75. Meng, Z.-D.; Zhu, L.; Choi, J.-G.; Chen, M.-L.; Oh, W.-C. Effect of Pt treated fullerene/TiO2 on the photocatalytic degradation of MO under visible light. J. Mater. Chem. 2011, 21, 7596–7603. [Google Scholar] [CrossRef]
  76. Meng, Z.-D.; Zhang, F.-J.; Zhu, L.; Park, C.-Y.; Ghosh, T.; Choi, J.-G.; Oh, W.-C. Synthesis and characterization of M-fullerene/TiO2 photocatalysts designed for degradation azo dye. Mater. Sci. Eng. C Mater. Biol. Appl. 2012, 32, 2175–2182. [Google Scholar] [CrossRef]
  77. Islam, M.T.; Hangkun, J.; Ting, Y.; Zubia, E.; Goos, A.G.; Bernal, R.A.; Botez, C.E.; Narayan, M.; Chan, C.K.; Noveron, J.C. Fullerene stabilized gold nanoparticles supported on titanium dioxide for enhanced photocatalytic degradation of methyl orange and catalytic reduction of 4-nitrophenol. J. Environ. Chem. Eng. 2018, 6, 3827–3836. [Google Scholar] [CrossRef]
  78. Meng, Z.-D.; Zhu, L.; Choi, J.-G.; Park, C.-Y.; Oh, W.-C. Preparation, characterization and photocatalytic behavior of WO3-fullerene/TiO2 catalysts under visible light. Nanoscale Res. Lett. 2011, 6, 459. [Google Scholar] [CrossRef]
  79. Ali, M.M.; Sandhya, K.Y. Visible light responsive titanium dioxide-cyclodextrin-fullerene composite with reduced charge recombination and enhanced photocatalytic activity. Carbon 2014, 70, 249–257. [Google Scholar] [CrossRef]
  80. Bai, W.; Krishna, V.; Wang, J.; Moudgil, B.; Koopman, B. Enhancement of nano titanium dioxide photocatalysis in transparent coatings by polyhydroxy fullerene. Appl. Catal. B Environ. 2012, 125, 128–135. [Google Scholar] [CrossRef]
  81. Lim, J.; Monllor-Satoca, D.; Jang, J.S.; Lee, S.; Choi, W. Visible light photocatalysis of fullerol-complexed TiO2 enhanced by Nb doping. Appl. Catal. B 2014, 153, 233–240. [Google Scholar] [CrossRef]
  82. Song, T.; Huo, J.; Liao, T.; Zeng, J.; Qin, J.; Zeng, H. Fullerene C-60 modified Cr2-xFexO3 nanocomposites for enhanced photocatalytic activity under visible light irradiation. Chem. Eng. J. 2016, 287, 359–366. [Google Scholar] [CrossRef]
  83. Song, T.; Zhang, P.; Zeng, J.; Wang, T.; Ali, A.; Zeng, H. Boosting the photocatalytic H-2 evolution activity of Fe2O3 polymorphs (alpha-, gamma- and beta-Fe2O3) by fullerene C-60 -modification and dye-sensitization under visible light irradiation. RSC Adv. 2017, 7, 29184–29192. [Google Scholar] [CrossRef]
  84. Lian, Z.; Xu, P.; Wang, W.; Zhang, D.; Xiao, S.; Li, X.; Li, G. C-60-Decorated CdS/TiO2 Mesoporous Architectures with Enhanced Photostability and Photocatalytic Activity for H-2 Evolution. ACS Appl. Mater. Interface 2015, 7, 4533–4540. [Google Scholar] [CrossRef]
  85. Chai, B.; Peng, T.; Zhang, X.; Mao, J.; Li, K.; Zhang, X. Synthesis of C-60-decorated SWCNTs (C-60-d-CNTs) and its TiO2-based nanocomposite with enhanced photocatalytic activity for hydrogen production. Dalton Trans. 2013, 42, 3402–3409. [Google Scholar] [CrossRef] [PubMed]
  86. Huo, J.; Zeng, H. A novel triphenylamine functionalized bithiazole-metal complex with C-60 for photocatalytic hydrogen production under visible light irradiation. J. Mater. Chem. A 2015, 3, 6258–6264. [Google Scholar] [CrossRef]
  87. Shahzad, K.; Tahir, M.B.; Sagir, M. Engineering the performance of heterogeneous WO3/[email protected]3B/Ni(OH)2 Photocatalysts for Hydrogen Generation. Int. J. Hydrog. Energy 2019, 44, 21738–21745. [Google Scholar] [CrossRef]
  88. Katsumata, K.-I.; Matsushita, N.; Okada, K. Preparation of TiO2-Fullerene Composites and Their Photocatalytic Activity under Visible Light. Int. J. Photoenergy 2012. [Google Scholar] [CrossRef]
  89. Grandcolas, M.; Ye, J.; Miyazawa, K. Titania nanotubes and fullerenes C-60 assemblies and their photocatalytic activity under visible light. Ceram. Int. 2014, 40, 1297–1302. [Google Scholar] [CrossRef]
  90. Bastakoti, B.P.; Ishihara, S.; Leo, S.-Y.; Ariga, K.; Wu, K.C.W.; Yamauchi, Y. Polymeric Micelle Assembly for Preparation of Large-Sized Mesoporous Metal Oxides with Various Compositions. Langmuir 2014, 30, 651–659. [Google Scholar] [CrossRef]
  91. Moor, K.J.; Valle, D.C.; Li, C.; Kim, J.-H. Improving the Visible Light Photoactivity of Supported Fullerene Photocatalysts through the Use of C-70 Fullerene. Environ. Sci. Technol. 2015, 49, 6190–6197. [Google Scholar] [CrossRef] [PubMed]
  92. Kumar, R.; Gleissner, E.H.; Tiu, E.G.; Yamakoshi, Y. C70 as a Photocatalyst for Oxidation of Secondary Benzylamines to Imines. Org. Lett. 2016, 18, 184–187. [Google Scholar] [CrossRef] [PubMed]
  93. Arbogast, J.W.; Foote, C.S. Photophysical properties of C70. J. Am. Chem. Soc. 1991, 113, 8886–8889. [Google Scholar] [CrossRef]
  94. Cho, E.-C.; Ciou, J.-H.; Zheng, J.-H.; Pan, J.; Hsiao, Y.-S.; Lee, K.-C.; Huang, J.-H. Fullerene C-70 decorated TiO2 nanowires for visible-light-responsive photocatalyst. Appl. Surf. Sci. 2015, 355, 536–546. [Google Scholar] [CrossRef]
  95. Oh, W.-C.; Ko, W.-B. Characterization and photonic properties for the Pt-fullerene/TiO2 composites derived from titanium (IV) n-butoxide and C-60. J. Ind. Eng. Chem. 2009, 15, 791–797. [Google Scholar] [CrossRef]
  96. Kanchanatip, E.; Grisdanurak, N.; Thongruang, R.; Neramittagapong, A. Degradation of paraquat under visible light over fullerene modified V-TiO2. React. Kinet. Mech. Catal. 2011, 103, 227–237. [Google Scholar] [CrossRef]
  97. Oh, W.-C.; Zhang, F.-J.; Chen, M.-L. Synthesis and characterization of V-C-60/TiO2 photocatalysts designed for degradation of methylene blue. J. Ind. Eng. Chem. 2010, 16, 299–304. [Google Scholar] [CrossRef]
  98. Meng, Z.-D.; Zhu, L.; Ye, S.; Sun, Q.; Ullah, K.; Cho, K.-Y.; Oh, W.-C. Fullerene modification CdSe/TiO2 and modification of photocatalytic activity under visible light. Nanoscale Res. Lett. 2013, 8, 1–10. [Google Scholar] [CrossRef]
  99. Pickering, K.D.; Wiesner, M.R. Fullerol-sensitized production of reactive oxygen species in aqueous solution. Environ. Sci. Technol. 2005, 39, 1359–1365. [Google Scholar] [CrossRef]
  100. Schreiner, K.M.; Filley, T.R.; Blanchette, R.A.; Bowen, B.B.; Bolskar, R.D.; Hockaday, W.C.; Masiello, C.A.; Raebiger, J.W. White-Rot Basidiomycete-Mediated Decomposition of C60 Fullerol. Environ. Sci. Technol. 2009, 43, 3162–3168. [Google Scholar] [CrossRef]
  101. Vileno, B.; Marcoux, P.R.; Lekka, M.; Sienkiewicz, A.; Fehér, T.; Forró, L. Spectroscopic and Photophysical Properties of a Highly Derivatized C60 Fullerol. Adv. Funct. Mater. 2006, 16, 120–128. [Google Scholar] [CrossRef]
  102. Husebo, L.O.; Sitharaman, B.; Furukawa, K.; Kato, T.; Wilson, L.J. Fullerenols revisited as stable radical anions. J. Am. Chem. Soc. 2004, 126, 12055–12064. [Google Scholar] [CrossRef] [PubMed]
  103. Trajković, S.; Dobrić, S.; Jaćević, V.; Dragojević-Simić, V.; Milovanović, Z.; Đorđević, A. Tissue-protective effects of fullerenol C60(OH)24 and amifostine in irradiated rats. Colloids Surf. B Biointerfaces 2007, 58, 39–43. [Google Scholar] [CrossRef] [PubMed]
  104. Krishna, V.; Noguchi, N.; Koopman, B.; Moudgil, B. Enhancement of titanium dioxide photocatalysis by water-soluble fullerenes. J. Colloid Interface Sci. 2006, 304, 166–171. [Google Scholar] [CrossRef] [PubMed]
  105. Krishna, V.; Yanes, D.; Imaram, W.; Angerhofer, A.; Koopman, B.; Moudgil, B. Mechanism of enhanced photocatalysis with polyhydroxy fullerenes. Appl. Catal. B 2008, 79, 376–381. [Google Scholar] [CrossRef]
  106. Park, Y.; Singh, N.J.; Kim, K.S.; Tachikawa, T.; Majima, T.; Choi, W. Fullerol-Titania Charge-Transfer-Mediated Photocatalysis Working under Visible Light. Chem. A Eur. J. 2009, 15, 10843–10850. [Google Scholar] [CrossRef] [PubMed]
  107. Seo, Y.S.; Lee, C.; Lee, K.H.; Yoon, K.B. 1:1 and 2:1 charge-transfer complexes between aromatic hydrocarbons and dry titanium dioxide. Angew. Chem. Int. Ed. Engl. 2005, 44, 910–913. [Google Scholar] [CrossRef]
  108. Ramakrishnan, A.; Neubert, S.; Mei, B.; Strunk, J.; Wang, L.; Bledowski, M.; Muhler, M.; Beranek, R. Enhanced performance of surface-modified TiO2 photocatalysts prepared via a visible-light photosynthetic route. Chem. Commun. 2012, 48, 8556–8558. [Google Scholar] [CrossRef]
  109. Velmurugan, R.; Swaminathan, M. An efficient nanostructured ZnO for dye sensitized degradation of Reactive Red 120 dye under solar light. Sol. Energy Mater. Sol. Cells 2011, 95, 942–950. [Google Scholar] [CrossRef]
  110. Chen, D.; Ye, J. Hierarchical WO3 Hollow Shells: Dendrite, Sphere, Dumbbell, and Their Photocatalytic Properties. Adv. Funct. Mater. 2008, 18, 1922–1928. [Google Scholar] [CrossRef]
  111. Xie, X.; Yang, H.; Zhang, F.; Li, L.; Ma, J.; Jiao, H.; Zhang, J. Synthesis of hollow microspheres constructed with α-Fe2O3 nanorods and their photocatalytic and magnetic properties. J. Alloys Compd. 2009, 477, 90–99. [Google Scholar] [CrossRef]
  112. Bae, K.W. Synthesis of SnO2-Mn-C60 Nanocomposites and Their Photocatalytic Activity for Degradation of Organic Dyes. Elastom. Compos. 2017, 52, 287–294. [Google Scholar]
  113. Di Paola, A.; Garcia-Lopez, E.; Marci, G.; Palmisano, L. A survey of photocatalytic materials for environmental remediation. J. Hazard. Mater. 2012, 211, 3–29. [Google Scholar] [CrossRef] [PubMed]
  114. Hong, S.K.; Lee, J.H.; Cho, B.H.; Ko, W.B. Preparation of a 70 fullerene-ZnO nanocomposite in an electric furnace and photocatalytic degradation of organic dyes. J. Ceram. Process. Res. 2011, 12, 212–217. [Google Scholar]
  115. Chang, K.; Mei, Z.; Wang, T.; Kang, Q.; Ouyang, S.; Ye, J. MoS2/Graphene Cocatalyst for Efficient Photocatalytic H2 Evolution under Visible Light Irradiation. ACS Nano 2014, 8, 7078–7087. [Google Scholar] [CrossRef]
  116. Yuan, X.; Wang, H.; Wang, J.; Zeng, G.; Chen, X.; Wu, Z.; Jiang, L.; Xiong, T.; Zhang, J.; Wang, H. Near-infrared-driven Cr(vi) reduction in aqueous solution based on a MoS2/Sb2S3 photocatalyst. Catal. Sci. Technol. 2018, 8, 1545–1554. [Google Scholar] [CrossRef]
  117. Yuan, X.; Jiang, L.; Liang, J.; Pan, Y.; Zhang, J.; Wang, H.; Leng, L.; Wu, Z.; Guan, R.; Zeng, G. In-situ synthesis of 3D microsphere-like In2S3/InVO4 heterojunction with efficient photocatalytic activity for tetracycline degradation under visible light irradiation. Chem. Eng. J. 2019, 356, 371–381. [Google Scholar] [CrossRef]
  118. Simon, T.; Bouchonville, N.; Berr, M.J.; Vaneski, A.; Adrović, A.; Volbers, D.; Wyrwich, R.; Döblinger, M.; Susha, A.S.; Rogach, A.L.; et al. Redox shuttle mechanism enhances photocatalytic H2 generation on Ni-decorated CdS nanorods. Nat. Mater. 2014, 13, 1013–1018. [Google Scholar] [CrossRef]
  119. Meng, Z.-D.; Ghosh, T.; Zhu, L.; Choi, J.-G.; Park, C.-Y.; Oh, W.-C. Synthesis of fullerene modified with Ag2S with high photocatalytic activity under visible light. J. Mater. Chem. 2012, 22, 16127–16135. [Google Scholar] [CrossRef]
  120. Di, J.; Xia, J.; Ji, M.; Wang, B.; Yin, S.; Zhang, Q.; Chen, Z.; Li, H. Advanced photocatalytic performance of graphene-like BN modified BiOBr flower-like materials for the removal of pollutants and mechanism insight. Appl. Catal. B 2016, 183, 254–262. [Google Scholar] [CrossRef]
  121. Yu, H.; Huang, B.; Wang, H.; Yuan, X.; Jiang, L.; Wu, Z.; Zhang, J.; Zeng, G. Facile construction of novel direct solid-state Z-scheme AgI/BiOBr photocatalysts for highly effective removal of ciprofloxacin under visible light exposure: Mineralization efficiency and mechanisms. J. Colloid Interface Sci. 2018, 522, 82–94. [Google Scholar] [CrossRef]
  122. Wang, X.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J.M.; Domen, K.; Antonietti, M. A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nat. Mater. 2009, 8, 76–80. [Google Scholar] [CrossRef] [PubMed]
  123. Jiang, L.; Yuan, X.; Zeng, G.; Liang, J.; Wu, Z.; Yu, H.; Mo, D.; Wang, H.; Xiao, Z.; Zhou, C. Nitrogen self-doped g-C3N4 nanosheets with tunable band structures for enhanced photocatalytic tetracycline degradation. J. Colloid Interface Sci. 2019, 536, 17–29. [Google Scholar] [CrossRef] [PubMed]
  124. Jiang, L.; Yuan, X.; Zeng, G.; Liang, J.; Wu, Z.; Wang, H.; Zhang, J.; Xiong, T.; Li, H. A facile band alignment of polymeric carbon nitride isotype heterojunctions for enhanced photocatalytic tetracycline degradation. Environ. Sci. Nano 2018, 5, 2604–2617. [Google Scholar] [CrossRef]
  125. Wu, Y.; Wang, H.; Tu, W.; Wu, S.; Liu, Y.; Tan, Y.Z.; Luo, H.; Yuan, X.; Chew, J.W. Petal-like CdS nanostructures coated with exfoliated sulfur-doped carbon nitride via chemically activated chain termination for enhanced visible-light–driven photocatalytic water purification and H2 generation. Appl. Catal. B 2018, 229, 181–191. [Google Scholar] [CrossRef]
  126. Ouyang, K.; Dai, K.; Chen, H.; Huang, Q.; Gao, C.; Cai, P. Metal-free inactivation of E. coli O157:H7 by fullerene/C3N4 hybrid under visible light irradiation. Ecotoxicol. Environ. Saf. 2017, 136, 40–45. [Google Scholar] [CrossRef]
  127. Zhang, S.; Arunachalam, P.; Abe, T.; Iyoda, T.; Nagai, K. Photocatalytic decomposition of N-methyl-2-pyrrolidone, aldehydes, and thiol by biphase and p/n junction-like organic semiconductor composite nanoparticles responsive to nearly full spectrum of visible light. J. Photochem. Photobiol. A Chem. 2012, 244, 18–23. [Google Scholar] [CrossRef]
  128. Ruoff, R.S.; Tse, D.S.; Malhotra, R.; Lorents, D.C. Solubility of fullerene (C60) in a variety of solvents. J. Phys. Chem. 1993, 97, 3379–3383. [Google Scholar] [CrossRef]
  129. Kyriakopoulos, J.; Papastavrou, A.T.; Panagiotou, G.D.; Tzirakis, M.D.; Triantafyllidis, K.S.; Alberti, M.N.; Bourikas, K.; Kordulis, C.; Orfanopoulos, M.; Lycourghiotis, A. Deposition of fullerene C-60 on the surface of MCM-41 via the one-step wet impregnation method: Active catalysts for the singlet oxygen mediated photooxidation of alkenes. J. Mol. Catal. A Chem. 2014, 381, 9–15. [Google Scholar] [CrossRef]
  130. Hou, W.-C.; Jafvert, C.T. Photochemistry of Aqueous C60 Clusters: Evidence of 1O2 Formation and its Role in Mediating C60 Phototransformation. Environ. Sci. Technol. 2009, 43, 5257–5262. [Google Scholar] [CrossRef] [PubMed]
  131. Tzirakis, M.D.; Vakros, J.; Loukatzikou, L.; Amargianitakis, V.; Orfanopoulos, M.; Kordulis, C.; Lycourghiotis, A. Gamma-Alumina-supported 60 fullerene catalysts: Synthesis, properties and applications in the photooxidation of alkenes. J. Mol. Catal. A Chem. 2010, 316, 65–74. [Google Scholar] [CrossRef]
  132. Lee, J.; Yamakoshi, Y.; Hughes, J.B.; Kim, J.-H. Mechanism of C60 Photoreactivity in Water: Fate of Triplet State and Radical Anion and Production of Reactive Oxygen Species. Environ. Sci. Technol. 2008, 42, 3459–3464. [Google Scholar] [CrossRef]
  133. Hotze, E.M.; Labille, J.; Alvarez, P.; Wiesner, M.R. Mechanisms of Photochemistry and Reactive Oxygen Production by Fullerene Suspensions in Water. Environ. Sci. Technol. 2008, 42, 4175–4180. [Google Scholar] [CrossRef] [PubMed]
  134. Vileno, B.; Sienkiewicz, A.; Lekka, M.; Kulik, A.J.; Forró, L. In vitro assay of singlet oxygen generation in the presence of water-soluble derivatives of C60. Carbon 2004, 42, 1195–1198. [Google Scholar] [CrossRef]
  135. Cho, M.; Lee, J.; Mackeyev, Y.; Wilson, L.J.; Alvarez, P.J.J.; Hughes, J.B.; Kim, J.-H. Visible Light Sensitized Inactivation of MS-2 Bacteriophage by a Cationic Amine-Functionalized C60 Derivative. Environ. Sci. Technol. 2010, 44, 6685–6691. [Google Scholar] [CrossRef] [PubMed]
  136. Snow, S.D.; Park, K.; Kim, J.-H. Cationic Fullerene Aggregates with Unprecedented Virus Photoinactivation Efficiencies in Water. Environ. Sci. Technol. Lett. 2014, 1, 290–294. [Google Scholar] [CrossRef]
  137. Mroz, P.; Tegos, G.P.; Gali, H.; Wharton, T.; Sarna, T.; Hamblin, M.R. Photodynamic therapy with fullerenes. Photochem. Photobiol. Sci. 2007, 6, 1139–1149. [Google Scholar] [CrossRef]
  138. Hou, W.-C.; Kong, L.; Wepasnick, K.A.; Zepp, R.G.; Fairbrother, D.H.; Jafvert, C.T. Photochemistry of Aqueous C60 Clusters: Wavelength Dependency and Product Characterization. Environ. Sci. Technol. 2010, 44, 8121–8127. [Google Scholar] [CrossRef]
  139. Hou, W.-C.; Jafvert, C.T. Photochemical Transformation of Aqueous C60 Clusters in Sunlight. Environ. Sci. Technol. 2009, 43, 362–367. [Google Scholar] [CrossRef]
  140. Lee, J.; Mackeyev, Y.; Cho, M.; Wilson, L.J.; Kim, J.-H.; Alvarez, P.J.J. C60 Aminofullerene Immobilized on Silica as a Visible-Light-Activated Photocatalyst. Environ. Sci. Technol. 2010, 44, 9488–9495. [Google Scholar] [CrossRef]
  141. Redmond, R.W.; Kochevar, I.E. Symposium-in-Print: Singlet Oxygen Invited Review. Photochem. Photobiol. 2006, 82, 1178–1186. [Google Scholar] [CrossRef]
  142. Foote, C.S.; Clennan, E.L. Properties and Reactions of Singlet Dioxygen. In Active Oxygen in Chemistry; Foote, C.S., Valentine, J.S., Greenberg, A., Liebman, J.F., Eds.; Springer: Dordrecht, The Netherlands, 1995; pp. 105–140. [Google Scholar]
  143. Lee, J.; Hong, S.; Mackeyev, Y.; Lee, C.; Chung, E.; Wilson, L.J.; Kim, J.H.; Alvarez, P.J. Photosensitized oxidation of emerging organic pollutants by tetrakis C(6)(0) aminofullerene-derivatized silica under visible light irradiation. Environ. Sci. Technol. 2011, 45, 10598–10604. [Google Scholar] [CrossRef]
  144. Choi, Y.; Ye, Y.; Mackeyev, Y.; Cho, M.; Lee, S.; Wilson, L.J.; Lee, J.; Alvarez, P.J.J.; Choi, W.; Lee, J. C60 aminofullerene-magnetite nanocomposite designed for efficient visible light photocatalysis and magnetic recovery. Carbon 2014, 69, 92–100. [Google Scholar] [CrossRef]
  145. Moor, K.J.; Kim, J.H. Simple synthetic method toward solid supported c60 visible light-activated photocatalysts. Environ. Sci. Technol. 2014, 48, 2785–2791. [Google Scholar] [CrossRef] [PubMed]
  146. Rogozea, E.A.; Meghea, A.; Olteanu, N.L.; Bors, A.; Mihaly, M. Fullerene-modified silica materials designed for highly efficient dyes photodegradation. Mater. Lett. 2015, 151, 119–121. [Google Scholar] [CrossRef]
  147. Wakimoto, R.; Kitamura, T.; Ito, F.; Usami, H.; Moriwaki, H. Decomposition of methyl orange using C60 fullerene adsorbed on silica gel as a photocatalyst via visible-light induced electron transfer. Appl. Catal. B 2015, 166–167, 544–550. [Google Scholar] [CrossRef]
  148. Kyriakopoulos, J.; Kordouli, E.; Bourikas, K.; Kordulis, C.; Lycourghiotis, A. Decolorization of Orange-G Aqueous Solutions over C-60/MCM-41 Photocatalysts. Appl. Sci. 2019, 9, 1958. [Google Scholar] [CrossRef]
Figure 1. Schematic illustration of the mechanochemical reaction between g-C3N4 and C60 in the presence of the LiOH catalyst in a sealed ball-mill crusher. Reproduced with permission from Reference [55]. Copyright 2017, RSC.
Figure 1. Schematic illustration of the mechanochemical reaction between g-C3N4 and C60 in the presence of the LiOH catalyst in a sealed ball-mill crusher. Reproduced with permission from Reference [55]. Copyright 2017, RSC.
Materials 13 02924 g001
Figure 2. TEM images of TiO2 (a) and TiO2/C60 (b). (c) HR-TEM image of TiO2/C60. (d) Diffuse reflectance spectroscopy (DRS) of TiO2/C60 and pure TiO2. (e) Free radical capture experiment within photocatalytic degradation of RhB. (f) Photocatalytic degradation towards RhB over the TiO2/fullerene nanocomposite under the visible light irradiation. Reproduced with permission from Reference [68]. Copyright 2016, Elsevier.
Figure 2. TEM images of TiO2 (a) and TiO2/C60 (b). (c) HR-TEM image of TiO2/C60. (d) Diffuse reflectance spectroscopy (DRS) of TiO2/C60 and pure TiO2. (e) Free radical capture experiment within photocatalytic degradation of RhB. (f) Photocatalytic degradation towards RhB over the TiO2/fullerene nanocomposite under the visible light irradiation. Reproduced with permission from Reference [68]. Copyright 2016, Elsevier.
Materials 13 02924 g002
Figure 3. SEM (a) and TEM (b) images of 18 wt % C70-TiO2. (c) UV-Vis DRS of the C70-TiO2 and pure TiO2. (d) Comparison of PL spectra over C70-TiO2, C60-TiO2 and TiO2. (e) Photocatalytic mechanisms of C70-TiO2 under UV and visible light illumination. Reproduced with permission from Reference [69]. Copyright 2015, RCS.
Figure 3. SEM (a) and TEM (b) images of 18 wt % C70-TiO2. (c) UV-Vis DRS of the C70-TiO2 and pure TiO2. (d) Comparison of PL spectra over C70-TiO2, C60-TiO2 and TiO2. (e) Photocatalytic mechanisms of C70-TiO2 under UV and visible light illumination. Reproduced with permission from Reference [69]. Copyright 2015, RCS.
Materials 13 02924 g003
Figure 4. UV-vis spectra (a), photocurrent density measured at 0.5 V in a 0.5 M aqueous Na2SO4 electrolyte (b) and PL spectra (c) excited by 280 nm of CdS/TiO2 and C60-CdS/TiO2 nanocomposites. (d) The mechanism of photocatalytic H2 generation over C60-CdS/TiO2. Reproduced with permission from Reference [84]. Copyright 2015, ACS.
Figure 4. UV-vis spectra (a), photocurrent density measured at 0.5 V in a 0.5 M aqueous Na2SO4 electrolyte (b) and PL spectra (c) excited by 280 nm of CdS/TiO2 and C60-CdS/TiO2 nanocomposites. (d) The mechanism of photocatalytic H2 generation over C60-CdS/TiO2. Reproduced with permission from Reference [84]. Copyright 2015, ACS.
Materials 13 02924 g004
Figure 5. UV-vis spectra (a), PL emission spectra (b) and transient photocurrent responses (c) in 0.5 M Na2SO4 solution of CdS and C60/CdS nanocomposites. (d) The photocatalytic rate of H2 generation over C60/CdS samples under visible light illumination. (e) Recyclability test of photodegradation towards RhB under visible light illumination over CdS and 0.4C60/CdS composite. (f) Comparison of Cd2+ concentrations in the solutions of CdS and 0.4C60/CdS photocatalysts after three cycles for RhB degradation. Reproduced with permission from Reference [43]. Copyright 2017, Elsevier.
Figure 5. UV-vis spectra (a), PL emission spectra (b) and transient photocurrent responses (c) in 0.5 M Na2SO4 solution of CdS and C60/CdS nanocomposites. (d) The photocatalytic rate of H2 generation over C60/CdS samples under visible light illumination. (e) Recyclability test of photodegradation towards RhB under visible light illumination over CdS and 0.4C60/CdS composite. (f) Comparison of Cd2+ concentrations in the solutions of CdS and 0.4C60/CdS photocatalysts after three cycles for RhB degradation. Reproduced with permission from Reference [43]. Copyright 2017, Elsevier.
Materials 13 02924 g005
Figure 6. (a) Photocurrent responses of Bi2TiO4F2, C60 (1 wt %) + Bi2TiO4F2 mixture and 1 wt % C60/Bi2TiO4F2. (b) Photocatalytic performance towards RhB degradation. (c) Recyclability test of the as-prepared composites 1 wt % C60/Bi2TiO4F2. (d) The mechanism of C60/Bi2TiO4F2 photocatalyst is presented under visible light irradiation. Reproduced with permission from Reference [73]. Copyright 2013, ACS.
Figure 6. (a) Photocurrent responses of Bi2TiO4F2, C60 (1 wt %) + Bi2TiO4F2 mixture and 1 wt % C60/Bi2TiO4F2. (b) Photocatalytic performance towards RhB degradation. (c) Recyclability test of the as-prepared composites 1 wt % C60/Bi2TiO4F2. (d) The mechanism of C60/Bi2TiO4F2 photocatalyst is presented under visible light irradiation. Reproduced with permission from Reference [73]. Copyright 2013, ACS.
Materials 13 02924 g006
Figure 7. (a) XRD patterns of g-C3N4/C60 samples and pristine g-C3N4. (b) High-resolution N 1s XPS spectra of g-C3N4/C60−12 wt % nanocomposite. (c) Photocatalytic H2 generation rates of the as-prepared samples. (d) A schematic of the photocatalytic H2 generation mechanism for the g-C3N4/C60 nanocomposite. Reproduced with permission from Reference [55]. Copyright 2017, RCS.
Figure 7. (a) XRD patterns of g-C3N4/C60 samples and pristine g-C3N4. (b) High-resolution N 1s XPS spectra of g-C3N4/C60−12 wt % nanocomposite. (c) Photocatalytic H2 generation rates of the as-prepared samples. (d) A schematic of the photocatalytic H2 generation mechanism for the g-C3N4/C60 nanocomposite. Reproduced with permission from Reference [55]. Copyright 2017, RCS.
Materials 13 02924 g007
Figure 8. HRTEM images of PbMoO4 (a) and C60-PbMoO4 (b). EDS spectrum measured from the edge (c) and the center of C60–PbMoO4 composite (d). (e) DRS of the C60–PbMoO4 samples and pure PbMoO4 composite. (f) Plot of (αhν)1/2 versus photon energy (hν) based on the DRS. Reproduced with permission from Reference [50]. Copyright 2013, Elsevier.
Figure 8. HRTEM images of PbMoO4 (a) and C60-PbMoO4 (b). EDS spectrum measured from the edge (c) and the center of C60–PbMoO4 composite (d). (e) DRS of the C60–PbMoO4 samples and pure PbMoO4 composite. (f) Plot of (αhν)1/2 versus photon energy (hν) based on the DRS. Reproduced with permission from Reference [50]. Copyright 2013, Elsevier.
Materials 13 02924 g008
Figure 9. Route for immobilization of aminofullerenes on functionalized silica gel. Reproduced with permission from Reference [140]. Copyright 2010, ACS.
Figure 9. Route for immobilization of aminofullerenes on functionalized silica gel. Reproduced with permission from Reference [140]. Copyright 2010, ACS.
Materials 13 02924 g009
Figure 10. (a) Photochemical furfuryl alcohol (FFA) degradation (measuring photosensitized 1O2 production) by aminofullerenes and aminofullerene/silica composites. Comparisons of degradation efficiency towards furfuryl alcohol (b) and ranitidine (RA) and cimetidine (CM) (c) by TiO2, carbon-doped TiO2 (C-TiO2), [email protected]3 and tetrakis aminoC60/silica. Reproduced with permission from Reference [140,143]. Copyright 2010, 2011, ACS.
Figure 10. (a) Photochemical furfuryl alcohol (FFA) degradation (measuring photosensitized 1O2 production) by aminofullerenes and aminofullerene/silica composites. Comparisons of degradation efficiency towards furfuryl alcohol (b) and ranitidine (RA) and cimetidine (CM) (c) by TiO2, carbon-doped TiO2 (C-TiO2), [email protected]3 and tetrakis aminoC60/silica. Reproduced with permission from Reference [140,143]. Copyright 2010, 2011, ACS.
Materials 13 02924 g010
Figure 11. (a) A schematic of photocatalytic mechanism of novel C70/MCM-41 photocatalyst. Photoinduced MS2 inactivation kinetics of C70/MCM-41 and porous N-TiO2 under visible light (b) and sunlight irradiation (c). Photodegradation kinetics of various PPCPs by C70/MCM-41 under visible irradiation (d) and corresponding dark controls (e). Reproduced with permission from Reference [91]. Copyright 2015, ACS.
Figure 11. (a) A schematic of photocatalytic mechanism of novel C70/MCM-41 photocatalyst. Photoinduced MS2 inactivation kinetics of C70/MCM-41 and porous N-TiO2 under visible light (b) and sunlight irradiation (c). Photodegradation kinetics of various PPCPs by C70/MCM-41 under visible irradiation (d) and corresponding dark controls (e). Reproduced with permission from Reference [91]. Copyright 2015, ACS.
Materials 13 02924 g011
Table 1. Summary of fullerene based photocatalysts for pollutant degradation.
Table 1. Summary of fullerene based photocatalysts for pollutant degradation.
Photocatalyst (Additive Amount)Synthesis Method (Fullerene Content)PollutantsExperimental Conditions (Light Source, Pollutant Concentration and React Time)Photocatalytic ActivityEnhancement FactorReference
TiO2/C60
(1 g/L)
In-situ growth
(2.0 wt %)
Methylene blue (MB)UV irradiation, 1.0 × 10−4 mol/L, 60 min99%around 75% for TiO2[67]
TiO2/C60
(1 g/L)
Ultrasonication–evaporation (1.0 wt %)RhB500 W Xe-lamp (>400 nm), 10 mg/L, 150 min95%below 5% for TiO2[68]
TiO2/C70
(1 g/L)
Hydrothermal synthesis
(8.5 wt %)
Sulfathiazole300 W Xenon lamp (>420 nm), 10 mg/mL, 180 min80%10% for TiO2[69]
ZnO/C60
(0.5 g/L)
Simple adsorption
(1.5 wt %)
MB8 W UV lamp (λ = 254 nm),
8 mg/L
k = 0.0569 min−13-times than ZnO[70]
ZnO/C60
(0.83 g/L)
Chemical vapor
(16.7 wt %)
Phenol1500 W xenon lamp simulating solar light, 20 mg/Lk = 0.160 min−11.22-times than ZnO[42]
ZnFe2O4@C60
(1 g/L)
Hydrothermal synthesisNorfloxacinSolar irradiation, 20 mL of 50 ppm norfloxacin, 90 min85%60% for ZnFe2O4[71]
WO3@C60Hydrothermal synthesis (4.0 wt %)MBVisible light, 90 min94%Inferior degradation efficiency for pure WO3[53]
[email protected]60 (ZnAlTi-LDO) 0.5 g/LPrecipitation (5%)Bisphenol A (BPA)300 W xenon lamp simulating visible light, 10 mg/L, 60 min80%below 10% for ZnAlTi-LDH[38]
CdS/C60
(1 g/L)
One-pot hydrothermal method (0.4 wt %)RhB300 W xenon lamp (>420 nm), 20 mL, 10 ppm of RhBk = 0.089 min−11.5-times than CdS[43]
C3N4/C60
(0.6 g/L)
Simple adsorption
(1.0 wt %)
RhB500 W xenon lamp (>420 nm), 50 mL, 1.0 × 10−5 mol l−1 RhB, 60 min97%54% for C3N4[45]
g-C3N4/C60
(0.5 g/L)
Calcination (0.03 wt %)MB, phenol500 W xenon lamp (>420 nm), MB (50 mL, 0.01 mM), phenol (50 mL, 5 ppm).k1 = 1.036 h−1,
k2 = 0.093 h−1
3.2- and 2.9-times than C3N4[35]
Ag3PO4/C60
(0.5 g/L)
Precipitation (2.0 wt %)Acid red 18 (AR18)400 W halogen lamp (420–780 nm, 21.5–23.0 mW cm−2), 50 mL, 6.5 × 10−5 mol/L of AR18, 60 min90%53% for Ag3PO4[31]
Ag3PO4/C60
(1 g/L)
Precipitation (5.0 mg/L)Methyl Orange (MO)300 W xenon lamp (>420 nm), 10 mg/Lk = 0.453 min−1k = 0.028 min−1 for Ag3PO4[72]
PbMoO4/C60
(0.4 g/L)
Hydrothermal synthesis (0.5 wt %)RhB18 W low-pressure mercury lamp as the UV light source, 50 mL of RhB (1 × 10−5 M), 2 h99%37% for PbMoO4[50]
Bi2WO6/C60
(1 g/L)
Simple adsorption (1.25 wt %)MB, RhB500 W xenon lamp (>420 nm), 1 × 10−5 mol/L RhB or MB (100 mL)k1 = 0.0099 min−1,
k2 = 0.0454 min−1
5.0- and 1.5-times than Bi2WO6[40]
BiOCl/C70
(1 g/L)
In-situ growth (1.0 wt %)RhB500 W xenon lamp (>420 nm), 10 mg/L, 30 min99.8%49.7% and 66.4% for BiOCl and P25 (TiO2)[39]
Bi2TiO4F2/C60Solvothermal method (1.0 wt %)RhBVisible light, 20 ppm RhB, 120 min93%65% for Bi2TiO4F2[73]
CNTs/BiVO4-C60
(2 g/L)
Hydrothermal synthesis (2.5 wt %)RhB300 W xenon lamp (>420nm), 100 mL, 0.01 mmol/L RhB, 30 min96.1%74.0% for BiVO4[51]
CNTs/Bi2MoO6-C60
(2 g/L)
Hydrothermal synthesis (2.5 wt %)RhB300 W xenon lamp (>420 nm), 100 mL, 0.01 mmol/L RhB, 30 min88.4%43.7% for Bi2MoO6[51]
Ag3PO4/Fe3O4/C60
(1 g/L)
Hydrothermal synthesis (5.0 wt %)MB400 W mercury lamp (>420 nm), 50 mL of MB (25 mg/L), 300 min95%33% for Ag3PO4[74]
TiO2/Pt-C60
(1 g/L)
Sol-gel method (7.5 wt %)MO8 W halogen lamp (400–790 nm), 50 mL, 1 × 10−5 mol/L of MOk = 3.67×10−3 min−11.58- and 16.4-times than Pt/TiO2 and TiO2[75]
TiO2/Pd-C60
(1 g/L)
Sol-gel method (21 wt %)MBUV lamp box (8 W, 365 nm), 50 mL, 1 × 10−4 mol/L of MBk = 0.0337 min−114-times than TiO2[76]
Au/TiO2-C60
(1 g/L)
Hydrothermal synthesis (3.25 wt %)MO500W tungsten halogen lamp, 20 mL, 10 mg/L of MO, 160 min95%47% for TiO2[77]
TiO2/CdS-C60
(1 g/L)
Sol-gel method (5.0 wt %)MB8 W halogen lamp (400–790 nm), 50 mL, 1 × 10−5 mol/L of MBk = 7.9×10−3 min−14.9- and 3.5-times than CdS/TiO2 and TiO2[56]
TiO2/WO3-C60
(1 g/L)
Sol-gel method (3.0 wt %)MO8 W halogen lamp (400–790 nm), 50 mL, 1 × 10−5 mol/L of MOk = 4.75×10−3 min−11.66- and 21.2-times than WO3/TiO2 and TiO2[78]
TiO2/CD/C60
(1 g/L)
Simple adsorption (1.5%)MB, 4-chlorophenol (4-CP)84 W light sources (>420 nm), MB (10 mL, 144 μM), 10 mg/L 4-CPk1 = 0.014 min−1,
k2 = 0.036 min−1
2- and 4.9-times than TiO2[79]
TiO2/Fullerol
(1 g/L)
Wet impregnationProcion red
MX-5B
16 solar UVA lamps (350 nm)k = 0.0128 min−12.6-times than TiO2[80]
TiO2/Fullerol
(1 g/L)
Wet impregnation (1.0 wt %)Formic acidHg lamp (365 nm)k = 91.0 µmol L−1 min−11.3-times than TiO2[59]
Nb-TiO2/Fullerol
(0.5 g/L)
Simple adsorption4-chlorophenol300-W Xe arc lamp (>420 nm)k = 13.9×10−3 min−13.3-times than P25[81]
k means rate constant of photocatalytic degradation, which is calculated by the relationship between−ln(C/C0) and t (C0 and C are the concentrations of pollutant in solution at times 0 and t, respectively).
Table 2. Summary of fullerene based photocatalysts for photocatalytic H2 generation.
Table 2. Summary of fullerene based photocatalysts for photocatalytic H2 generation.
Photocatalyst (Additive Amount)Synthesis Method (Fullerene Content)Experimental ConditionsPhotocatalytic Rate of H2 GenerationEnhancement FactorReference
CdS/C60
(0.5 g/L)
Hydrothermal synthesis (0.4 wt %)300 W xenon lamp (>420 nm), 50 mL aqueous solution containing 10 vol% lactic acid and 1 wt % Pt1.73 mmol h−1 g−12.3 Times of pure CdS[43]
WO3@C60
(0.5 g/L)
Hydrothermal synthesis (4 wt %)300 W xenon lamp (>420 nm), Triethanolamine (TEA)154 µmol h−1 g−12 times of pure WO3[53]
MoS2/C60
(0.5 g/L)
Ball milling method (2.8 wt %)300 W xenon lamp (>420 nm), 20 mL aqueous solution containing 3.5 mg Eosin Y (EY) and 1 mL TEA6.89 mmol h−1 g−19.3 times of ball-milled MoS2[54]
g-C3N4/C60
(1 g/L)
Ball milling method (12 wt %)300 W xenon lamp (>420 nm), 100 mL aqueous solution containing 17.5 mg EY and 5 mL TEA266 µmol h−1 g−14.0 times higher than pristine C3N4[55]
Cr1.3Fe0.7O3-C60 (5 mg/78 mL)Simple adsorption (3%)300 W xenon lamp (>420 nm), 78 mL 10 vol% TEA aqueous solution220.5 µmol h−1 g−12 times of the Cr1.3Fe0.7O3[82]
Fe2O3/C60 (5 mg/78 mL)Simple adsorption (0.5~1 wt %)300 W xenon lamp (>420 nm), 78 mL 10 vol% TEA aqueous solutionβ-Fe2O3/C60: 1665 µmol h−1 g−1;
α-Fe2O3/C60: 202.9 µmol h−1 g−1;
γ-Fe2O3/C60: 169.4 µmol h−1 g−1
β-Fe2O3: 169.4 µmol h−1 g−1;
α-Fe2O3: 80.6 µmol h−1 g−1;
γ-Fe2O3: 252 µmol h−1 g−1;
C3N4: 82.7 µmol h−1 g−1
[83]
CdS/TiO2-C60 (50 mg/80 mL)An ion-exchanged method (0.5 wt %)Low power UV-LEDs (420 nm), 80 mL solution (0.25 M Na2S, 0.25 M Na2SO3)120.6 µmol h−1 g−18.5 times of CdS/TiO2[84]
TiO2/C60-d-CNTs (1 g/L)Hydrothermal synthesis (5 wt %)300 W xenon lamp (>420 nm), 100 mL 10 vol% TEA aqueous solution651 µmol h−1 g−1208 µmol h−1 g−1 for pure TiO2[85]
g-C3N4/graphene/ C60 (2 g/L)Wet impregnationLight-emitting diode (>420 nm), 50 mL solution containing 1 wt‰ Pt and 10 vol% TEA545 µmol h−1 g−150.8 and 4.24 times of graphene/g-C3N4 and C60/g-C3N4[19]
(2TPABTz)–metal complex/C60Simple adsorption (2 wt %)300 W xenon lamp (>420 nm), an aqueous lactic acid (LA)2TPABTz-Cu/C60: 4.05 mmol h−1 g−1;
2TPABTz-Co/C60: 3.77 mmol h−1 g−1;
2TPABTz-Ru/C60: 6.12 mmol h−1 g−1
2TPABTz-Cu: 4.05 mmol h−1 g−1;
2TPABTz-Co: 3.77 mmol h−1 g−1;
2TPABTz-Ru: 6.12 mmol h−1 g−1;
TiO2 (P25): 0.072 mmol h−1 g−1
[86]
WO3/C60@Ni3B/Ni(OH)2 2 g/LPhoto-deposition technique500 W xenon lamp (>420nm), 100 mL 10 vol% TEA aqueous solution1.578 mmol h−1 g−19.6 times of pure photocatalyst[87]
Back to TopTop