Next Article in Journal
Fabrication of Hierarchically Porous Reduced Graphene Oxide/SnIn4S8 Composites by a Low-Temperature Co-Precipitation Strategy and Their Excellent Visible-Light Photocatalytic Mineralization Performance
Next Article in Special Issue
Recent Progress on MOF-Derived Nanomaterials as Advanced Electrocatalysts in Fuel Cells
Previous Article in Journal
Promotional Effect of Ce on Iron-Based Catalysts for Selective Catalytic Reduction of NO with NH3
Previous Article in Special Issue
An Oxygen Reduction Study of Graphene-Based Nanomaterials of Different Origin
Article Menu

Export Article

Catalysts 2016, 6(8), 111; https://doi.org/10.3390/catal6080111

Review
Nanocarbons with Different Dimensions as Noble-Metal-Free Co-Catalysts for Photocatalysts
School of Materials Science and Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
*
Authors to whom correspondence should be addressed.
Academic Editor: Frédéric Jaouen
Received: 19 May 2016 / Accepted: 21 July 2016 / Published: 28 July 2016

Abstract

:
In this review, we provide an overview of recent progress in nanocarbons with different dimensions as noble-metal-free co-catalysts for photocatalysts. We put emphasis on the interface engineering between nanocarbon co-catalysts and various semiconductor photocatalysts and the novel properties generating of nanocarbon co-catalysts, also including the synthesis and application of nanocarbon-based photocatalyst composites.
Keywords:
nanocarbon co-catalysts; dimensionality; interface engineering; photocatalysis

1. Introduction

In the last decades, many techniques have been developed for solving energy crises and environmental pollution problems. However, most of the techniques have shortcomings of low efficiency, difficulty of complete removal of pollutants, production of secondary pollution, and high energy consumption. More economical and effective techniques are desired. In 1972, Fujishima and Honda [1], for the first time, found that the single crystal TiO2 electrode could produce hydrogen by splitting water under UV irradiation. In 1978, Halmann [2] used a P-type semiconductor of GaP as a photoelectric electrode to reduce CO2-water solution into CH3OH. These two pioneering works revealed the potential capability of solar photocatalysis technology in solving the problems of energy crises and environmental pollution [3,4,5]. However, it is a long way for solar photocatalysis techniques in large scale industrial applications because of the low solar energy utilization, and high recombination rate of photoinduced electrons and holes of photocatalysts [6,7,8].
Various strategies have been developed for improving the photocatalytic performance of photocatalysts, such as morphology control, band gap engineering, and loading of co-catalysts on semiconductor photocatalysts [9,10]. Loading of co-catalysts on semiconductor photocatalysts and forming interfacial heterostructures has been proved an effective way for absorbing a broader spectrum of solar energy and gaining efficient charge separation and migration [11,12,13]. Here, co-catalyst means a certain substance which, itself, is a rather weak catalyst, but which greatly increases the activity of a given catalyst; also called a promoter. Noble metals and their compounds are frequently selected as co-catalysts. Noble metal co-catalysts, including Pt, Pd, Rh, or RuO2, can significantly enhance the photocatalytic performance of semiconductor photocatalysts [14]. However, noble metals are rare and expensive, which hinder their practical application. Efficient and noble metal-free cocatalysts are urgently required. Nanocarbon materials with low dimension and specific morphology, such as zero dimensional (0D) fullerene and nano-onions, one dimensional (1D) nanofibers and nanotubes, and two dimensional (2D) graphene, exhibit unique physical and chemical properties including high electrical conductivity, high surface area, and chemical stability [15]. Thus, nanocarbon materials can be employed as excellent co-catalysts for semiconductor photocatalysts.
Different dimensional nanocarbon co-catalysts can form various dimensional interfaces with different dimensional semiconductor photocatalysts as shown in Figure 1. Three modes of interface will form including point-to-point, line-to-line and surface-to-surface in nanocarbon co-catalysts/semiconductor photocatalysts heterostructures. In photocatalytic reactions, such as H2 evolution from photocatalytic water splitting, when photocatalysts absorb suitable light, the electrons will be excited and transfer from the valence band to the conduction band and positive holes are left in the valence band. Water molecules are reduced by the electrons to form H2 and are oxidized by the holes to form O2. However, negative electrons and positive holes have a tendency to recombine. The photocatalytic activity depends on the ability of the photocatalyst to create electron–hole pairs and the separation efficiency of photogenerated electron-hole pairs [16]. For nanocarbon-based photocatalysts, photogenerated electrons can transfer from the conduction band of semiconductor photocatalysts to nanocarbon materials through the intimate interface between them, which greatly inhibit the recombination of photoinduced electrons and holes. So, as the channel for electron transfer, the dimensions of the interface will be critical for effective separation of photoinduced electrons and holes.
Some reviews about nanocarbon-based materials for photocatalysis have been published [17,18]. However, most of them only focused on TiO2 photocatalysts or graphene-based photocatalytic composites. In this short review, we provide an overview of recent progress in nanocarbons with different dimensions as noble-metal-free co-catalysts for photocatalysts. We put emphasis on the interface engineering between nanocarbon co-catalysts and various semiconductor photocatalysts, and the novel properties generating of nanocarbon co-catalysts.

2. 0D Carbon Materials as Cocatalysts

Fullerenes, as typical 0D nanocarbon materials, possess some special properties and have attracted much attention [19]. C60 and C70 are the most common fullerenes. It has been reported that fullerenes with unique electronic properties can be used as co-catalysts for improving transfer efficiency of photoinduced electrons and actually enhance photocatalytic activities [20,21,22,23,24,25,26].

2.1. 0D/0D

TiO2, as one of the most researched photocatalytic materials, has attracted much attention [3,27,28] due to its advantages of nontoxicity, low cost, and high photocatalytic activity [29,30]. Oh et al. [31] employed an improved oxidation method to synthesize the fullerene/TiO2 composites. One of the advantages of these composites is that there are more reactive sites on the surface of oxidized fullerenes than non-oxidized fullerenes, which can be helpful for high-quality dispersion of TiO2 particles. The photocatalytic activity of fullerene/TiO2 composites was evaluated by photocatalytic decomposition of methylene blue (MB) under UV light irradiation. It is no doubt that the composites exhibit enhanced photocatalytic activity. Different from TiO2, photocorrosion of ZnO during light irradiation hinders their practical application in the field of photocatalysis and its applications are limited to light-emitting diodes [32], gas sensors [33], and so forth. [34]. Fu et al. [35] synthesized C60-coated ZnO photocatalysts. The coating of C60 enhances the photocatalytic activity and inhibits the photocorrosion of ZnO. It was found that the coverage of C60 on the surface of ZnO nanoparticles determined the enhancement degree of photocatalytic activity, indicating the crucial role of hybridized interaction between C60 and ZnO. From the viewpoint of efficient utilization of solar energy, visible light-response photocatalysts with high photocatalytic activity are desired. Song et al. [36] synthesized C60 modified Cr2-xFexO3 heterostructured photocatalysts and employed them in photocatalytic H2 evolution from water splitting under visible light irradiation. The C60-Cr1.3Fe0.3O3 with an optimized band structure (Eg = 1.5 eV) exhibits strong visible light absorption capability. The good dispersion of C60 on the surface of Cr1.3Fe0.3O3 nanoparticles supplies more reactive sites and the point-to-point interface promotes the transfer of photoinduced electrons. Consequently, the H2 evolution ability of C60-Cr1.3Fe0.3O3 is two times higher than that of pure Cr1.3Fe0.3O3 nanoparticles.
Similar to C60, another fullerene C70 is a closed-shell configuration consisting of 35 bonding molecular orbital with 70 p-electrons [37]. Wang and coworkers [38] fabricated fullerene C70-modified TiO2 (C70-TiO2) by titanium sulfate and functionalized C70. The covalent bonds (Ti-O-C = O or Ti-O-C) formed by C70 and surface atoms of TiO2 nanoparticles not only generate point-to-point interfaces between the functionalized C70 and TiO2, but also slightly reduce the crystallite size of TiO2, as well as extend absorption edge of TiO2 to the visible light region. The photocatalytic degradation rate of sulfathiazole by using C70-TiO2 hybrid as photocatalysts is 1.6 times higher than that of C60-TiO2 hybrid due to the larger photo cross-sectional area, larger delocalization effect, and higher electron affinity of C70 (Figure 2).

2.2. 0D/1D

Long et al. [39] synthesized C60 nanoparticles incorporated TiO2 nanorods. The photocatalytic activity of C60/TiO2 nanorods is about 3.3 times higher than that of TiO2 nanorods. The high specific surface area plays an important role and the electronic interactions between C60 and TiO2 enhance the absorption of visible light (Figure 3). Grandcolas et al. [40] reported that after the hybridization with C60, the absorption capacity in the visible light region and photocatalytic activity of titania nanotubes (TiNTs) are all enhanced. It was found that C60 distributes both inside and outside of TiNTs. Photoinduced electrons are delivered from the 1D main photocatalyst to 0D C60 nanoparticles through the point-to-point interface, inhibiting the electron-hole recombination.

2.3. 0D/2D

To further extend the surface area of photocatalysts, two-dimensional nanosheets may be an ideal candidate and also act as a supporting matrix to disperse C60 uniformly. Li and coworkers [41] synthesized fullerene C60-enhanced Bi2TiO4F2 hierarchical microspheres and employed the obtained photocatalysts to degrade Rhodamine B (RhB) and Eosin Y (EY) under visible light irradiation. C60/Bi2TiO4F2 not only has higher photocatalytic activity than pure Bi2TiO4F2, but also shows improved stability (Figure 4). The photocatalytic activity of C60/Bi2TiO4F2 is also higher than that of a physical mixture of C60 and Bi2TiO4F2, further confirming the strong interaction between C60 and Bi2TiO4F2.
Although many achievements have confirmed that the employment of 0D carbon materials as co-catalysts can actually enhance the photocatalytic performance of semiconductor photocatalysts, these materials are difficult to homogeneously disperse on the surface of main photocatalysts. Even though the 0D nanocarbon particles can be dispersed on the surface of main photocatalysts, only point-to-point interfaces may form regardless of the dimensions of the main photocatalysts. Furthermore, 0D nanoparticles have a tendency to agglomerate and some large clusters with irregular agglomerate are universal [35], which induce poor interfacial contact between nanocarbon particles and main photocatalysts.

3. 1D Nanocarbon Materials as Co-Catalysts

1D carbon materials including carbon nanotube (CNTs) and carbon nanofibers (CNFs) have been studied for many years due to their unique properties. For instance, CNTs are studied as hydrogen storage materials due to their large surface area, hollow and layered structure [42]. As a supporting matrix, CNTs can offer high surface area and specific functional groups for efficient adsorption of reactants [43,44]. CNTs are also famous for their high mechanical strength, making them suitable for a large number of applications [45,46,47,48]. Their properties of excellent conductivity and 1D structure make them an ideal candidate co-catalyst for photocatalyts [49]. Many researchers focused on this field and made some achievements.

3.1. 1D/0D

It is known that 0D particles have a tendency of agglomeration due to the high surface energy [50]. Loading 0D photocatalysts nanoparticles on the surface of supports with high specific surface area and confinement effect can prevent their agglomeration as well as favor the recovery of photocatalysts. Especially if the support possesses excellent conductivity, the transfer of photogenerated electrons will be promoted and recombination of electrons and holes can be inhibited efficiently.
Peng et al. [51] synthesized 1D multiwall carbon nanotubes (MWCNTs)/0D CdS composites. MWCNTs function as supporting matrix and also play a role of electron transfer channels due to their intrinsic conductive properties (Figure 5). The contact interface between MWCNTs and CdS can be responsible for the enhanced photocatalytic performance because it ensures the timely transfer of electrons and stabilizes CdS nanoparticles. The enhancement of photocatalytic performance for degrading methyl red was also observed for 1D CNT/0D ZnO nanocomposites [52]. Xia et al. [53] reported the fabrication of MWCNTs/TiO2 composites and employed them to reduce CO2 with H2O. The improved photocatalytic performance and major product HCOOH demonstrated that the separation of photogenerated electron and hole pairs is remarkable due to the interaction between MWCNTs and TiO2. Noble metals as co-catalysts can bring significant improvement during the photocatalytic reaction [14,54,55]. However, their high price inhibits the particle’s applications. Researchers hope to find some non-noble metals to replace novel metals [56,57,58]. Zhang et al. [59] reported the synthesis of Mo-decorated TiO2/CNTs (Mo-CT) composites. In this system, three parts play their own duty, respectively, and the interaction between them dramatically enhances the photocatalytic activity. Mo clusters play the role of accepting photoinduced electrons came from the conduction band of TiO2, achieving the separation of photoinduced electrons and holes. CNTs act as both visible light absorption sites and electron transfer channels and, at the same time, TiO2 plays a role in electron excitation [60].

3.2. 1D/1D

Different from 0D photocatalysts, 1D photocatalysts can form 1D interface with 1D nanocarbon co-catalysts at the same direction, thus bringing stronger interaction, which is beneficial to the photocatalytic reaction. However, it is actually hard to control two kinds of 1D material to array on one direction and form a line-to-line interface homogeneously. Natarajan [61] recently reported the fabrication of MWCNT-loaded TiO2 nanotube (TNT) composites by a hydrothermal method. They tried to obtain 1D/1D composites, but it was found that most of the junctions between MWCNTs and TiO2 nanotubes are still shaped as points. The excellent durability and stability of the obtained composites for degrading dyes seem to be due to the point-to-point interface, but not the line-to-line interface.

3.3. 1D/2D

Different from the 1D/1D mode, an intimate and larger contacted line-to-line interface can form when 1D nanocarbon co-catalysts combine with 2D photocatalysts. Chen at al. [62] synthesized hierarchical core-shell carbon [email protected]2S4 composites by controlling the in situ growth of ZnIn2S4 nanosheets on carbon nanofibers (CNFs). This preparation process not only ensures the uniform growth of nanosheets, but also avoids the agglomeration of ZnIn2S4. It is believed that the stacking force between ZnIn2S4 nuclei and nanofibers promotes the in situ formation of ZnIn2S4 (Figure 6A). The synergistic effects formed by the increased active sites, electron-tunneling effect and junctions, leading to excellent photocatalytic activity (Figure 6B).

4. 2D Nanocarbon Materials as Co-Catalysts

Graphene, a new class of nanocarbon material with honeycomb network of monolayer carbon atoms, different from 0D fullerene and 1D CNTs or CNFs, has attracted increasing attention due to their excellent electrical conductivity, large surface area, and high chemical stability [63,64]. Graphene can be used as an electron-transport matrix due to its excellent electrical conductivity and perfect 2D feature, and then take the place of noble metals as co-catalysts for enhancing the photocatalytic performance by offering strong interaction, as shown in Figure 1. It has been extensively explored to improve the utilization of solar energy by introducing graphene into photocatalysts. [65,66,67,68,69].

4.1. 2D/0D

With smart design, 0D photocatalyst nanoparticles can be dispersed on 2D graphene nanosheets homogeneously or be wrapped into the nanosheets. The functional groups anchored on the surface of graphene nanosheets can form chemical bonding with photocatalyst particles to avoid their agglomeration during the photocatalytic reaction. It is well-known that the availability of charge carriers has a decisive role in photocatalytic activity. Therefore, any method which can improve the utilization of photogenerated carriers and lengthen the lifetime of charge carriers is desired [70].
As one of the most attractive visible light-response photocatalysts, CdS is prone to photocorrosion and aggregation during the photoreactions [71]. Zhang et al. [72] synthesized CdS/graphene composites by evenly spreading CdS nanoparticles on 2D graphene nanosheets. The introduction of graphene is helpful for increasing the light absorption intensity. However, excessive graphene (more than 5% of weight ratio) obscures the light illumination reaching the surface of the CdS nanoparticles and leads to a decrease of photocatalytic activity. An appropriate amount of graphene promotes not only the transfer of electrons but also the capacity of visible light absorption. In addition, the introduction of graphene could have influence on the crystallinity and the specific surface areas of CdS nanoparticles. However, graphene is not easy to be dispersed in water, which makes it difficult to contact semiconductor nanoparticles with graphene in aqueous solution. GO with hydrophilic oxygen-containing groups is easy to be dispersed in aqueous solution, so GO is usually used as a graphene precursor [73,74,75]. Zhu et al. [76] employed GO and TiCl3 as starting materials and synthesized graphene/TiO2 composites. TiO2 with a size of about 7 nm fully cover both surfaces of the graphene nanosheets. The growth of TiO2 on the surface of GO plays an important role in enhancing photocurrent response [77] and, thus, improving the photocatalytic ability. Li and coworkers [78] synthesized CdS cluster-decorated graphene nanosheets via a solvothermal method (Figure 7). In this system, GO and cadmium acetate (Cd(Ac)2) were used as the graphene precursor and CdS precursor, respectively. The composites with 1.0 wt% of graphene and 0.5 wt% of Pt exhibit the highest H2-production rate of 1.12 mmol·h−1. This value of H2-production rate is much higher than other reports about CdS/graphene composite photocatalysts (as shown in Table 1), which may be due to the presence of 0.5 wt% of Pt in this photocatalytic reaction system. This means that for reaching the highest photocatalytic performance, graphene still cannot completely replace the noble metal co-catalyst.
Recently, it has been demonstrated that doping graphene with hetero atoms can effectively modulate the electronic and catalytic properties of graphene. Jia et al. [79] synthesized N-doped graphene/CdS nanocomposites by annealing graphene in NH3 gas and combining it with CdS nanoparticles. When N-graphene is ca. 2 wt%, the N-graphene/CdS composites display enhanced photocatalytic ability and stability for H2 evolution from water splitting under visible light irradiation, which is higher than that of the physical mixture of N-graphene and CdS, as well as undoped-graphene/CdS composites. These results strongly suggest the crucial role of the intimate contact between 2D N-graphene nanosheets and 0D CdS nanoparticles in transferring of photogenerated carriers [80]. Mou et al. [81] also reported that N-doped graphene/TiO2 exhibit a higher photocatalytic activity. The enhanced photocatalytic activity of N-doped graphene based photocatalysts is attributed to the higher electrical conductivity of N-doped graphene because, after nitrogen doping, the free carrier density of graphene is improved [82]. Xu’s group [83] further studied the synergistic effect of graphitic N and pyrrolic N in N-doped graphene/TiO2 nanocomposites. It was suggested that the doped graphitic-N functions as an electron-transfer mediator for the photo-generated electrons while the doped pyrrolic-N serves as the oxygen-reduction active site to promote the following interfacial catalytic reaction. From the above research, N-doped graphene has been proved to be effective to enhance photocatalytic performance.
Graphene-based binary nanocomposite photocatalysts show that graphene coupled to another single component can improve the photocatalytic ability. In addition to binary nanocomposites, hybrid nanomaterials with multicomponents are expected to provide enhanced photocatalytic performance as well as multifunctional properties for photocatalysts. Some groups synthesized graphene-based ternary system to improve the photocatalytic performance further [84,85,86,87,88]. MoS2 is often used as co-catalyst in photocatalytic reactions [89,90]. Xiang et al. [88] synthesized TiO2/MoS2/graphene composites by preparing the layered MoS2 and graphene hybrid firstly. The layered MoS2/graphene co-catalysts function not only as active adsorption sites but also as photocatalytic reaction centers which are important for H2 evolution. Zhang and coworkers [91] prepared the ternary CdS-graphene-TiO2 hybrid photocatalysts. In the ternary system, the CdS nanoparticles evenly disperse on the surface of graphene nanosheets and the TiO2 nanoparticles decorate the CdS-graphene base uniformly. Compared with matrix binary CdS-graphene, the ternary CdS-graphene-TiO2 hybrid exhibit higher photocatalytic activity.

4.2. 2D/1D

1D photocatalysts with high aspect ratios have attracted attention [92,93]. Compared with 0D structures, 1D structures have fast and long-distance electron-transport capability, high surface area, and pore volume [94,95,96]. When 1D semiconductor photocatalysts are combined with graphene nanosheets, a line-to-line interface will form, which is the key factor for electron transfer.
CdS nanowires/RGO nanosheets 1D/2D nanocomposites were designed and synthesized by Liu [97]. Their photocatalytic performance was characterized by selectively reducing nitro-containing compounds in an aqueous phase. Compared with CdS nanowires, the CdS-nanowires/RGO nanocomposites exhibit significantly enhanced photocatalytic activity. Yu and coworkers [98] synthesized CdS nanorods/RGO nanocomposites. CdS nanorods evenly spread on the surface of RGO nanosheets. RGO plays as an ideal platform for the nucleation and growth of CdS nanorods and has no obvious influence on the morphology of the CdS nanorods [99,100]. For photocatalytic reduction of CO2 to CH4, RGO/CdS nanocomposite photocatalysts with an optimal RGO content of 0.5 wt% exhibit the highest CH4-production rate of 2.51 mmol·h−1·g−1, 10 times more than pure CdS nanorods, and even better than Pt-CdS composites. Shen et al. [101] chose ZnxCd1-xS (ZCS) as main photocatalysts, whose band gap can be adjusted by changing the Cd/Zn ratio, and synthesized ZnxCd1-xS ultrathin nanorods/RGO sheets 1D/2D nanocomposites (ZCS/RGO). The presence of RGO can avoid the agglomeration of ZnxCd1-xS ultrathin nanorods and simultaneously improve the conductivity of photocatalysts. The strong contact line-to-line interface, as shown in Figure 8, is beneficial for fast collection and transfer of electrons thus enhances the photocatalytic performance and stability of ultrathin nanorod photocatalysts (Figure 8).
Liu et al. [102] synthesized GO/TiO2 2D/1D composites with a configuration of TiO2 nanorods with 2–3 nm diameter and 20–30 nm length on the whole large GO sheets. It was found that when using the composites as photocatalysts for the degradation of MB, the degradation rate in the second cycle is faster than that in the first cycle because GO in the composites is reduced to RGO. Liu and coworkers [103] fabricated N-doped TiO2 nanowires/N-doped graphene (N-TiO2/NG) nanocomposites. N-TiO2/NG nanocomposites exhibit higher photocatalytic performance than TiO2 nanowire/graphene composites and N-doped TiO2 nanowire/graphene composites for degradation of MB under visible light irradiation. N-doped graphene restrains the recombination of photogenerated holes and electrons and N doping extends the absorpton spectrum of TiO2 to the visible light region.

4.3. 2D/2D

A larger intimate interface can provide higher photocatalytic activity because of the more effectively transfer of photoinduced electrons, and lower electrons and holes recombination rate. In view of graphene’s two-dimensional structure, an ideal interface formed with photocatalysts should be face-to-face interface (Figure 1). However, in most cases, the structures of photocatalysts are 0D nanoparticles or 1D nanorods. To completely utilize 2D nature of graphene, a more efficient face-to-face contact between 2D photocatalysts and graphene nanosheets is highly desirable.
Nitrogenous compounds have been studied as photocatalysts for a few decades, such as Ta3N5 [104], GaN [105,106], and graphitic carbon nitride (g-C3N4/g-CN) [107,108]. g-C3N4 has attracted dramatically increasing interest for its unique properties of Earth-abundant elements (C and N) and suitable band gap (2.7 eV) [109,110,111,112]. g-C3N4 is generally synthesized by nitrogen-rich precursors such as dicyandiamide, urea, melamine, and so forth [113,114], so g-C3N4 is nontoxic and cheap. However, its drawback, the low charge carrier mobility, inhibits the separation of electrons and holes and restricts its photocatalytic applications [115,116]. Considering the unique properties of graphene, researchers attempted to combine those two materials [117,118,119] in pursuit of superior photocatalytic performance.
Xiang et al. [119] reported the fabrication of graphene/g-C3N4 composites by a combined impregnation-chemical reduction strategy with melamine and GO as precursors. During the reaction, GO is reduced to graphene and melamine is decomposed to g-C3N4. GO sheets contained versatile oxygen-containing groups [85], pre-absorb melamine molecules and, thus, possess a compact structure with g-C3N4 sandwiched between graphene sheets. Graphene sheets act as a conductive path for efficiently transferring photogenerated electrons. The H2 production rate of the graphene/g-C3N4 composite is 451 μmol·h−1·g−1, 3.07 times more than pure g-C3N4. Toing’s group [120] employed a photocatalytic reduction method to produce RGO/g-C3N4 photocatalysts and evaluated its photocatalytic performance by degradation of phenol under visible light irradiation. They suggested that due to the presence of an aromatic network in both g-C3N4 and RGO, the RGO can interact with g-C3N4 via π-π stacking, which can promote the electron-hole separation and improve the interfacial charge transfer. Although g-C3N4, with the band gap of 2.7 eV, can be excited by visible light, the utilization of solar energy is still very low. Using RGO to narrow the photocatalyst band gap to achieve higher photocatalytic activities under visible light has been demonstrated by a number of groups [121]. Li et al. [122] synthesized cross-linked g-C3N4/RGO (CN/RGO) nanocomposites with a tunable band structure (Figure 9). They demonstrated that the band gap of g-C3N4/RGO composites can be readily controlled by changing the weight ratio of cyanamide to GO in precursor materials. A suitable RGO ratio can narrow the band gap, shift the valence band edge positively, and enhance electronic conductivity.
It has attracted intensive attention that combining with RGO can narrow the band gap of g-C3N4/RGO composites and enhance the photocatalytic performance [119,122]. Most explanations attribute those phenomena to the interactions between graphene and g-C3N4. However, why do the interactions between constituents bring those results? Which atom plays the key role during the photocatalytic processes? The theoretical understanding is lacking until Xu and coworkers reported their opinions [118]. Xu et al. demonstrated that the O atom plays a crucial role in the RGO-based composites. They believed that the interfacial interaction at the g-C3N4/RGO interface mainly depend on the density of O atom. Thus, it can be said that the narrowing of the band gap is dependent on the concentration of O atom. They also found the negatively-charged O atom in the RGO can act as active sites during photocatalytic activities. Since the O atom plays the key role in the photocatalytic system can GO, with versatile oxygen-containing groups on the basal planes and the edges [123], bring comparable or even greater photocatalytic performance than graphene? Dai et al. [124] fabricated g-C3N4/GO composites by anchoring g-C3N4 nanosheets on GO sheets. Different from g-C3N4/RGO composites, g-C3N4/GO composites display the same absorption edge with pure g-C3N4, but it extends broader background absorption in the visible light region. GO is not only a simple matrix for dispersion, but it also acts as an electron acceptor and enhances light absorption. During the degradation test, the composites exhibit enhanced photocatalytic performance under visible light irradiation 27.4 times higher than P25 photocatalyst and 3.7 times higher than pure g-C3N4 powder. Compared with these systems which required complicated processes, Yu [117] employed a one-step calcination method and synthesized GO-modified porous g-C3N4 (porous g-C3N4/GO). Due to the porous structure and heterojunction formed between g-C3N4 and GO, the photocatalytic performance of porous g-C3N4/GO for MB degradation is six times higher than that of pure g-C3N4.
To date, research on changing the morphology of TiO2 to get the more intimate connection between TiO2 and graphene has been confirmed to be effective for enhancing the transfer of photogenerated electrons. Xiang et al. [125] synthesized graphene-modified titania nanosheets by a microwave-hydrothermal method. GO is reduced to RGO and TiO2 nanosheets with exposed (001) facets formed on the surface of RGO sheets with face-to-face orientation. The TiO2/RGO composites with an optimal graphene content of 1.0 wt% demonstrate a more than 41 times enhancement of H2 production activity compared with pure TiO2.
As a typical 2D metal sulfide photocatalyst, molybdenum disulfide (MoS2) with a layered structure has been studied extensively [126,127]. Hou et al. [128] presented the fabrication of 2D porous g-C3N4 nanosheets/nitrogen-doped graphene/layered MoS2 (CNNS/NRGO/MoS2) ternary nanocomposites. They pointed out that the layered structure of MoS2 can shorten the charge transport distance and time by promoting charge separation and transfer at CNNS/MoS2 interfaces (sheet to sheet); the porous structure of g-C3N4 can provide a large surface area, thus, increasing the efficient light absorption; the nitrogen doping can enhance the electrical conductivity of graphene, thus, enhancing the transfer of photogenerated electrons and promote the separation of electrons and holes. The photocatalytic activities of this hybridization were evaluated by oxidation of MB and reduction of Cr (VI). The prolonged lifetime of photogenerated carriers, the extended absorption edge and the higher photocurrent density are all attributed to the unique ternary nanostructure.

5. Summary and Outlook

For enhancing the absorption capacity of visible light and the separation of photogenerated electrons and holes, co-catalysts are often considered in designing photocatalysts. Nanocarbon materials with low dimension and specific morphology, such as 0D fullerene and nano-onions, 1D nanofibers and nanotubes, and 2D graphene, possess unique physical and chemical properties, including high electrical conductivity, high surface area, and chemical stability. Thus, nanocarbon materials can be employed as excellent noble-metal free co-catalysts for semiconductor photocatalysts. Different dimensional nanocarbon co-catalysts can form different dimensional interface with different dimensional semiconductor photocatalysts including point-to-point, line-to-line, and face-to-face modes. The effective separation of electrons and holes pairs, prolonged photogenerated charge lifetime and shorten transfer channels which are beneficial to photocatalysis are bought by the junction between nanocarbon materials and photocatalysts. To maximize the photocatalytic performance, reasonably designing the structure of nanocarbons/semiconductor nanocomposite photocatalysts is crucial. Diverse types of composite photocatalysts composed of different dimensional nanocarbons and main photocatalysts have been researched (as shown in Table 1) such as 0D nanocarbons with different dimensional main photocatalysts (0D/0D, 0D/1D, and 0D/2D), 1D nanocarbons with different dimensional main photocatalysts (1D/0D, 1D/1D, and 1D/2D), and 2D nanocarbons with different dimensional main photocatalysts (2D/0D, 2D/1D, and 2D/2D). Diverse synthesis approaches and techniques have been developed including directly decomposition of precursors, chemical deposition, microwave technique, hydrothermal/solvothermal techniques, and sol-gel processing. The obtained nanocomposites exhibited higher photocatalytic performance than main photocatalysts components due to the synergetic effects between nanocarbon co-catalysts and main photocatalysts. Heteroatom doping or multi-components photocatalysts were also adopted to further promote the separation of photogenerated electrons and holes.
Without any doubt, these nanocarbon materials with different dimensions and specific properties are promising co-catalysts for semiconductor photocatalysts. So far, the strategies for the synthesis of nanocarbon/main photocatalyst composites are still being explored and some intrinsic mechanisms are not fully understood. Therefore, more general synthesis method and advanced measurement approaches are needed for both scientific research and applications. It is still a long journey to develop general and simple synthetic strategies and understand the basic fundamental formation mechanisms, as well as the practical applications of nanocarbon-based photocatalysts.

Acknowledgments

The authors gratefully acknowledge the financial support of National Natural Science Foundation of China (NSFC) (21101166, 51272157, 51472160), Key Basic Research Program of Shanghai Municipal Science and Technology Commission (12JC1406900, 13NM1401102), Innovation Program of Shanghai Municipal Education Commission (14YZ084), the Hujiang Foundation of China (B14006), and the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Fujishima, A. Electrochemical photolysis of water at a semiconductor electrode. Nature 1972, 238, 37–38. [Google Scholar] [CrossRef] [PubMed]
  2. Halmann, M. Photoelectrochemical reduction of aqueous carbon dioxide on p-type gallium phosphide in liquid junction solar cells. Nature 1978, 275, 115–116. [Google Scholar] [CrossRef]
  3. Ma, G.; Hisatomi, T.; Domen, K. Semiconductors for photocatalytic and photoelectrochemical solar water splitting. Chem. Soc. Rev. 2014, 43, 7520–7535. [Google Scholar]
  4. Li, C.; Yuan, J.; Han, B.; Jiang, L.; Shangguan, W. TiO2 nanotubes incorporated with CdS for photocatalytic hydrogen production from splitting water under visible light irradiation. Int. J. Hydrog. Energy 2010, 35, 7073–7079. [Google Scholar] [CrossRef]
  5. Zhuang, Z.; Peng, Q.; Li, Y. Controlled synthesis of semiconductor nanostructures in the liquid phase. Chem. Soc. Rev. 2011, 40, 5492–5513. [Google Scholar] [CrossRef] [PubMed]
  6. Zhao, L.; Geng, F.; Di, F.; Guo, L.H.; Wan, B.; Yang, Y.; Zhang, H.; Sun, G. Polyamine-functionalized carbon nanodots: a novel chemiluminescence probe for selective detection of iron(iii) ions. RSC Adv. 2014, 4, 45768–45771. [Google Scholar] [CrossRef]
  7. Preethi, V.; Kanmani, S. Photocatalytic hydrogen production using Fe2O3-based core shell nano particles with ZnS and CdS. Int. J. Hydrog. Energy 2014, 39, 1613–1622. [Google Scholar] [CrossRef]
  8. Xiang, Q.; Yu, J.; Jaroniec, M. Graphene-based semiconductor photocatalysts. Chem Soc. Rev. 2012, 41, 782–796. [Google Scholar] [CrossRef] [PubMed]
  9. Kołacz, K.; Gajewska, M.; Komornicki, S.; Radecka, M. The effect of GO deposition on the photoelectrochemical properties of TiO2 nanotubes. Int. J. Hydrog. Energy 2016, 41, 7538–7547. [Google Scholar] [CrossRef]
  10. Su, J.; Zhu, L.; Chen, G. Ultrasmall graphitic carbon nitride quantum dots decorated self-organized TiO2 nanotube arrays with highly efficient photoelectrochemical activity. Appl. Catal. Environ. 2016, 186, 127–135. [Google Scholar] [CrossRef]
  11. Zeng, R.; Sun, Z.; Cao, S.; Shen, R.; Liu, Z.; Xiong, Y.; Long, J.; Zheng, J.; Zhao, Y.; Shen, Y.; Wang, D. Facile synthesis of Ag-doped ZnCdS nanocrystals and transformation into Ag-doped ZnCdSSe nanocrystals with Se treatment. RSC Adv. 2015, 5, 1083–1090. [Google Scholar] [CrossRef]
  12. Liu, R.; Wang, P.; Wang, X.; Yu, H.; Yu, J. UV- and Visible-Light Photocatalytic Activity of Simultaneously Deposited and Doped Ag/Ag(I)-TiO2 Photocatalyst. J. Phys. Chem. 2012, 116, 17721–17728. [Google Scholar]
  13. Moniz, S.J.; Shevlin, S.A.; Martin, D.J.; Guo, Z.X.; Tang, J. Visible-light driven heterojunction photocatalysts for water splitting-a critical review. Energy Env. Sci. 2015, 8, 731–759. [Google Scholar] [CrossRef]
  14. Aazam, E.S. Photocatalytic oxidation of cyanide under visible light by Pt doped AgInS2 nanoparticles. J. Ind. Eng. Chem. 2014, 20, 4008–4013. [Google Scholar] [CrossRef]
  15. Ampelli, C.; Perathoner, S.; Centi, G. Carbon-based catalysts: opening new scenario to develop next-generation nano-engineered catalytic materials. Chin. J. Catal. 2014, 35, 783–791. [Google Scholar] [CrossRef]
  16. Zhang, F.; Li, C. Semiconductor-Based Photocatalytic Water Splitting. In Solar to Chemical Energy Conversion; Masakazu, S., Katsushi, F., Shinichiro, N., Eds.; Springer International Publishing: Cham, Switzerland, 2016; pp. 299–317. [Google Scholar]
  17. Tan, L.L.; Chai, S.P.; Mohamed, A.R. Synthesis and applications of graphene-based TiO2 photocatalysts. ChemSusChem. 2012, 5, 1868–1882. [Google Scholar] [CrossRef] [PubMed]
  18. Stankovich, S.; Dikin, D.A.; Dommett, G.H.; Kohlhaas, K.M.; Zimney, E.J.; Stach, E.A.; Piner, R.D.; Nguyen, S.T.; Ruoff, R.S. Graphene-based composite materials. Nature 2006, 442, 282–286. [Google Scholar] [CrossRef] [PubMed]
  19. Haddon, R. Chemistry of the fullerenes: The manifestation of strain in a class of continuous aromatic molecules. Science 1993, 261, 1545–1550. [Google Scholar] [CrossRef] [PubMed]
  20. 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. [Google Scholar] [CrossRef]
  21. 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 2016, 60, 184–194. [Google Scholar] [CrossRef] [PubMed]
  22. 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. Environ. 2015, 166, 544–550. [Google Scholar] [CrossRef]
  23. Cho, E.C.; Ciou, J.H.; Zheng, J.H.; Pan, J.; Hsiao, Y.S.; Lee, K.C.; Huang, J.H. Fullerene C70 decorated TiO2 nanowires for visible-light-responsive photocatalyst. Appl. Surf. Sci. 2015, 355, 536–546. [Google Scholar] [CrossRef]
  24. Kim, K.H.; Ko, J.W.; Ko, W.B. Preparation and kinetics of nanocomposites using WO3 with carbon nanomaterials for photocatalytic degradation of organic dyes. Asian J. Chem. 2016, 28, 194. [Google Scholar] [CrossRef]
  25. Qi, K.; Selvaraj, R.; Al Fahdi, T.; Al-Kindy, S.; Kim, Y.; Wang, G.C.; Tai, C.W.; Sillanpää, M. Enhanced photocatalytic activity of anatase-TiO2 nanoparticles by fullerene modification: A theoretical and experimental study. Appl. Surf. Sci. 2016, 22, 1498–1504. [Google Scholar]
  26. 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] [PubMed]
  27. Liu, E.; Kang, L.; Yang, Y.; Sun, T.; Hu, X.; Zhu, C.; Liu, H.; Wang, Q.; Li, X.; Fan, J. Plasmonic Ag deposited TiO2 nano-sheet film for enhanced photocatalytic hydrogen production by water splitting. Nanotechnology 2014, 25, 165401. [Google Scholar] [CrossRef] [PubMed]
  28. Li, L.; Yan, J.; Wang, T.; Zhao, Z.J.; Zhang, J.; Gong, J.; Guan, N. Sub-10 nm rutile titanium dioxide nanoparticles for efficient visible-light-driven photocatalytic hydrogen production. Nat. Commun. 2015, 6, 5881. [Google Scholar] [CrossRef] [PubMed]
  29. Wang, C.C.; Hsueh, Y.C.; Su, C.Y.; Kei, C.C.; Perng, T.P. Deposition of uniform Pt nanoparticles with controllable size on TiO2-based nanowires by atomic layer deposition and their photocatalytic properties. Nanotechnology 2015, 26, 254002. [Google Scholar] [CrossRef] [PubMed]
  30. Wang, S.; Pan, L.; Song, J.J.; Mi, W.; Zou, J.J.; Wang, L.; Zhang, X. Titanium-defected undoped anatase TiO2 with p-type conductivity, room-temperature ferromagnetism, and remarkable photocatalytic performance. J. Am. Chem. Soc. 2015, 137, 2975–2983. [Google Scholar] [CrossRef] [PubMed]
  31. 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]
  32. Huang, X.; Li, Z.; Wang, S.; Chi, D.; Chua, S.J. Solution-grown ZnO films towards transparent and smart dual-color light-emitting diode. ACS Appl. Mater. Interfaces 2016, 8, 15482–15488. [Google Scholar] [CrossRef] [PubMed]
  33. Qi, J.; Zhang, H.; Lu, S.; Li, X.; Xu, M.; Zhang, Y. High performance indium-doped ZnO gas sensor. J. Nanomater. 2015, 2015, 74. [Google Scholar] [CrossRef]
  34. Ghosh, M.; Ghosh, S.; Seibt, M.; Rao, K.Y.; Peretzki, P.; Rao, G.M. Ferroelectric origin in one-dimensional undoped ZnO towards high electromechanical response. Crystengcomm 2015, 18, 622–630. [Google Scholar] [CrossRef]
  35. Fu, H.; Xu, T.; Zhu, S.; Zhu, Y. Photocorrosion Inhibition and Enhancement of Photocatalytic Activity for ZnO via Hybridization with C60. Environ. Sci. Technol. 2008, 42, 8064–8069. [Google Scholar] [CrossRef]
  36. Song, T.; Huo, J.; Liao, T.; Zeng, J.; Qin, J.; Zeng, H. Fullerene [C60] modified Cr2−xFexO3 nanocomposites for enhanced photocatalytic activity under visible light irradiation. Chem. Eng. J. 2016, 287, 359–366. [Google Scholar] [CrossRef]
  37. Scuseria, G.E. The equilibrium structure of C70. An ab initio Hartree-Fock study. Chem. Phys. Lett. 1991, 180, 451–456. [Google Scholar] [CrossRef]
  38. Wang, S.; Liu, C.; Dai, K.; Cai, P.; Chen, H.; Yang, C.; Huang, Q. Fullerene C70-TiO2 hybrids with enhanced photocatalytic activity under visible light irradiation. J. Mater. Chem. A 2015, 3, 21090–21098. [Google Scholar] [CrossRef]
  39. Long, Y.; Lu, Y.; Huang, Y.; Peng, Y.; Lu, Y.; Kang, S.Z.; Mu, J. Effect of C60 on the photocatalytic activity of TiO2 nanorods. J. Phys. Chem. C 2009, 113, 13899–13905. [Google Scholar] [CrossRef]
  40. Grandcolas, M.; Ye, J.; Miyazawa, K. Titania nanotubes and fullerenes C60 assemblies and their photocatalytic activity under visible light. Ceram. Int. 2014, 40, 1297–1302. [Google Scholar] [CrossRef]
  41. Li, G.; Jiang, B.; Li, X.; Lian, Z.; Xiao, S.; Zhu, J.; Zhang, D.; Li, H. C60/Bi2TiO4F2 heterojunction photocatalysts with enhanced visible-light activity for environmental remediation. ACS Appl. Mater. Interfaces 2013, 5, 7190–7197. [Google Scholar] [CrossRef] [PubMed]
  42. Han, M.; Zhao, Q.; Zhu, Z.; Hu, Y.; Tao, Z.; Chen, J. The enhanced hydrogen storage of micro-nanostructured hybrids of Mg(BH4)2-carbon nanotubes. Nanoscale 2015, 7, 18305–18311. [Google Scholar] [CrossRef] [PubMed]
  43. Fu, L.; Lai, G.; Zhang, H.; Yu, A. One-pot synthesis of multipod ZnO-carbon nanotube-reduced graphene oxide composites with high performance in photocatalysis. J. Nanosci. Nanotechnol. 2015, 15, 4325–4331. [Google Scholar] [CrossRef] [PubMed]
  44. Zhang, F.; Xie, F.; Xu, H.; Liu, J.; Oh, W.C. Characterization of Pd/TiO2 embedded in multi-walled carbon nanotube catalyst with a high photocatalytic activity. Kinet. Catal. 2013, 54, 297–306. [Google Scholar] [CrossRef]
  45. Koziol, K.; Vilatela, J.; Moisala, A.; Motta, M.; Cunniff, P.; Sennett, M.; Alan, W. High-performance carbon nanotube fiber. Science 2007, 318, 1892–1895. [Google Scholar] [CrossRef] [PubMed]
  46. Wang, S.G.; Zhang, Q.; Yang, D.J.; Sellin, P.J.; Zhong, G.F. Multi-walled carbon nanotube-based gas sensors for NH3 detection. Diamond Related Mater. 2004, 13, 1327–1332. [Google Scholar] [CrossRef]
  47. Filleter, T.; Espinosa, H.D. Multi-scale mechanical improvement produced in carbon nanotube fibers by irradiation cross-linking. Carbon 2013, 56, 1–11. [Google Scholar] [CrossRef]
  48. Zhang, L.L.; Zhao, X. Carbon-based materials as supercapacitor electrodes. Chem. Soc. Rev. 2009, 38, 2520–2531. [Google Scholar] [CrossRef] [PubMed]
  49. Chen, P.; Wang, L.; Wang, P.; Kostka, A.; Wark, M.; Muhler, M.; Beranek, R. CNT-TiO2-δ composites for improved co-catalyst dispersion and stabilized photocatalytic hydrogen production. Catalysts 2015, 5, 270–285. [Google Scholar] [CrossRef]
  50. Woan, K.; Pyrgiotakis, G.; Sigmund, W. Photocatalytic carbon-nanotube-TiO2 composites. Adv. Mater. 2009, 21, 2233–2239. [Google Scholar] [CrossRef]
  51. Peng, T.; Zeng, P.; Ke, D.; Liu, X.; Zhang, X. Hydrothermal preparation of multiwalled carbon nanotubes (MWCNTs)/CdS nanocomposite and its efficient photocatalytic hydrogen production under visible light irradiation. Energy Fuels 2011, 25, 2203–2210. [Google Scholar] [CrossRef]
  52. Wang, X.; Yao, S.; Li, X. Sol-gel Preparation of CNT/ZnO nanocomposite and its photocatalytic property. Chin. J. Chem. 2009, 27, 1317–1320. [Google Scholar] [CrossRef]
  53. Xia, X.H.; Jia, Z.J.; Yu, Y.; Liang, Y.; Wang, Z.; Ma, L.L. Preparation of multi-walled carbon nanotube supported TiO2 and its photocatalytic activity in the reduction of CO2 with H2O. Carbon 2007, 45, 717–721. [Google Scholar] [CrossRef]
  54. Tanaka, A.; Sakaguchi, S.; Hashimoto, K.; Kominami, H. Preparation of Au/TiO2 with Metal Cocatalysts Exhibiting Strong Surface Plasmon Resonance Effective for Photoinduced Hydrogen Formation under Irradiation of Visible Light. ACS Catal. 2013, 3, 79–85. [Google Scholar] [CrossRef]
  55. Seery, M.K.; George, R.; Floris, P.; Pillai, S.C. Silver doped titanium dioxide nanomaterials for enhanced visible light photocatalysis. J. Photochem. Photobiol. Chem. 2007, 189, 258–263. [Google Scholar] [CrossRef]
  56. Wang, X.; Ling, D.; Wang, Y.; Long, H.; Sun, Y.; Shi, Y.; Chen, Y.; Jing, Y.; Sun, Y.; Dai, Y. N-doped graphene quantum dots-functionalized titanium dioxide nanofibers and their highly efficient photocurrent response. J. Mater. Res. 2014, 29, 1408–1416. [Google Scholar] [CrossRef]
  57. Yu, K.; Song, M.; Gao, X.; Hou, C.; Liang, J. Preparation and Photocatalytic Property of Nickel-Doped Titanium Dioxide Nanotubes. Synth. React. Inorg. Metal.-Org. Nano-Metal. Chem. 2014, 45, 1576–1579. [Google Scholar] [CrossRef]
  58. Venditti, F.; Cuomo, F.; Ceglie, A.; Avino, P.; Russo, M.V.; Lopez, F. Visible light caffeic acid degradation by carbon-doped titanium dioxide. Langmuir 2015, 31, 3627–3634. [Google Scholar] [CrossRef] [PubMed]
  59. Zhang, F.J.; Oh, W.C. Visible light photocatalytic properties of novel molybdenum treated carbon nanotube/titania composites. Bull. Mater. Sci. 2011, 34, 543–549. [Google Scholar] [CrossRef]
  60. Liu, B.; Xu, Y.; Cui, J.; Wang, S.; Wang, T. Carbon nanotubes-dispersed TiO2, nanoparticles with their enhanced photocatalytic activity. Mater. Res. Bull. 2014, 59, 278–282. [Google Scholar] [CrossRef]
  61. Natarajan, T.S.; Lee, J.Y.; Bajaj, H.C.; Jo, W.K.; Tayade, R.J. Synthesis of multiwall carbon nanotubes/TiO2 nanotube composites with enhanced photocatalytic decomposition efficiency. Catal. Today 2016. [Google Scholar] [CrossRef]
  62. Chen, Y.; Tian, G.; Ren, Z.; Pan, K.; Shi, Y.; Wang, J.; Fu, H. Hierarchical core-shell carbon [email protected]2S4 composites for enhanced hydrogen evolution performance. ACS Appl. Mater. Interfaces 2014, 6, 13841–13849. [Google Scholar] [CrossRef] [PubMed]
  63. Bonaccorso, F.; Colombo, L.; Yu, G.; Stoller, M.; Tozzini, V.; Ferrari, A.C.; Ruoff, R.S.; Pellegrini, V. Graphene, related two-dimensional crystals, and hybrid systems for energy conversion and storage. Science 2015, 347, 1246501. [Google Scholar] [CrossRef] [PubMed]
  64. Perreault, F.; de Faria, A.F.; Elimelech, M. Environmental applications of graphene-based nanomaterials. Chem. Soc. Rev. 2015, 44, 5861–5896. [Google Scholar] [CrossRef] [PubMed]
  65. Xiang, Q.; Lang, D.; Shen, T.; Liu, F. Graphene-modified nanosized Ag3PO4 photocatalysts for enhanced visible-light photocatalytic activity and stability. Appl. Catal. B Environ. 2015, 162, 196–203. [Google Scholar] [CrossRef]
  66. Liu, J.; Xue, Y.; Zhang, M.; Dai, L. Graphene-based materials for energy applications. MRS Bull. 2012, 37, 1265–1272. [Google Scholar] [CrossRef]
  67. Huang, X.; Qi, X.; Boey, F.; Zhang, H. Graphene-based composites. Chem. Soc. Rev. 2012, 41, 666–686. [Google Scholar] [CrossRef] [PubMed]
  68. An, X.; Yu, J.C. Graphene-based photocatalytic composites. RSC Adv. 2011, 1, 1426. [Google Scholar] [CrossRef]
  69. Iwashina, K.; Iwase, A.; Ng, Y.H.; Amal, R.; Kudo, A. Z-schematic water splitting into H2 and O2 using metal sulfide as a hydrogen-evolving photocatalyst and reduced graphene oxide as a solid-state electron mediator. J. Am. Chem. Soc. 2015, 137, 604–607. [Google Scholar] [CrossRef] [PubMed]
  70. Zhang, G.; Li, G.; Wang, X. Surface Modification of Carbon Nitride Polymers by Core-Shell Nickel/Nickel Oxide Cocatalysts for Hydrogen Evolution Photocatalysis. ChemCatChem 2015, 7, 2864–2870. [Google Scholar] [CrossRef]
  71. Chen, Z.; Liu, S.; Yang, M.Q.; Xu, Y.J. Synthesis of uniform CdS nanospheres/graphene hybrid nanocomposites and their application as visible light photocatalyst for selective reduction of nitro organics in water. ACS Appl. Mater. Interfaces 2013, 5, 4309–4319. [Google Scholar] [CrossRef] [PubMed]
  72. Zhang, N.; Zhang, Y.; Pan, X.; Fu, X.; Liu, S.; Xu, Y.J. Assembly of CdS nanoparticles on the two-dimensional graphene scaffold as visible-light-driven photocatalyst for selective organic transformation under ambient conditions. J. Phys. Chem. C 2011, 115, 23501–23511. [Google Scholar] [CrossRef]
  73. Zhang, Y.; Zhang, N.; Tang, Z.R.; Xu, Y.J. Improving the photocatalytic performance of graphene-TiO2 nanocomposites via a combined strategy of decreasing defects of graphene and increasing interfacial contact. Phys. Chem. Chem. Phys. 2012, 14, 9167–9175. [Google Scholar] [CrossRef] [PubMed]
  74. Zhang, X.Y.; Li, H.P.; Cui, X.L.; Lin, Y. Graphene/TiO2 nanocomposites: Synthesis, characterization and application in hydrogen evolution from water photocatalytic splitting. J. Mater. Chem. 2010, 20, 2801. [Google Scholar] [CrossRef]
  75. Peng, T.; Li, K.; Zeng, P.; Zhang, Q.; Zhang, X. Enhanced photocatalytic hydrogen production over graphene oxide–cadmium sulfide nanocomposite under visible light irradiation. J. Phys. Chem. C 2012, 116, 22720–22726. [Google Scholar] [CrossRef]
  76. Zhu, C.; Guo, S.; Wang, P.; Xing, L.; Fang, Y.; Zhai, Y.; Dong, S. One-pot, water-phase approach to high-quality graphene/TiO2 composite nanosheets. Chem. Commun. 2010, 46, 7148–7150. [Google Scholar] [CrossRef] [PubMed]
  77. Guo, C.X.; Yang, H.B.; Sheng, Z.M.; Lu, Z.S.; Song, Q.L.; Li, C.M. Layered graphene/quantum dots for photovoltaic devices. Angew. Chem. Int. Ed. 2010, 49, 3014–3017. [Google Scholar] [CrossRef] [PubMed]
  78. Li, Q.; Guo, B.; Yu, J.; Ran, J.; Zhang, B.; Yan, H.; Gong, J.R. Highly efficient visible-light-driven photocatalytic hydrogen production of CdS-cluster-decorated graphene nanosheets. J. Am. Chem. Soc. 2011, 133, 10878–10884. [Google Scholar] [CrossRef] [PubMed]
  79. Jia, L.; Wang, D.H.; Huang, Y.X.; Xu, A.W.; Yu, H.Q. Highly durable N-doped graphene/CdS nanocomposites with enhanced photocatalytic hydrogen evolution from water under visible light irradiation. J. Phys. Chem. C 2011, 115, 11466–11473. [Google Scholar] [CrossRef]
  80. Soin, N.; Sinha Roy, S.; Roy, S.; Hazra, K.S.; Misra, D.S.; Lim, T.H.; Hetherington, C.J.; McLaughlin, J.A. Enhanced and stable field emission from in situ nitrogen-doped few-layered graphene nanoflakes. J. Phys. Chem. C 2011, 115, 5366–5372. [Google Scholar] [CrossRef]
  81. Mou, Z.; Wu, Y.; Sun, J.; Yang, P.; Du, Y.; Lu, C. TiO2 nanoparticles-functionalized N-doped graphene with superior interfacial contact and enhanced charge separation for photocatalytic hydrogen generation. ACS Appl. Mater. Interfaces 2014, 6, 13798–13806. [Google Scholar] [CrossRef] [PubMed]
  82. Wu, M.; Cao, C.; Jiang, J.Z. Light non-metallic atom (B, N, O and F)-doped graphene: A first-principles study. Nanotechnology 2010, 21, 505202. [Google Scholar] [CrossRef] [PubMed]
  83. Xu, Y.; Mo, Y.; Tian, J.; Wang, P.; Yu, H.; Yu, J. The synergistic effect of graphitic N and pyrrolic N for the enhanced photocatalytic performance of nitrogen-doped graphene/TiO2 nanocomposites. Appl. Catal. B Environ. 2016, 181, 810–817. [Google Scholar] [CrossRef]
  84. Yan, J.; Ye, Q.; Wang, X.; Yu, B.; Zhou, F. CdS/CdSe quantum dot co-sensitized graphene nanocomposites via polymer brush templated synthesis for potential photovoltaic applications. Nanoscale 2012, 4, 2109–2116. [Google Scholar] [CrossRef] [PubMed]
  85. Park, W.I.; Lee, C.H.; Lee, J.M.; Kim, N.-J.; Yi, G.-C. Inorganic nanostructures grown on graphene layers. Nanoscale 2011, 3, 3522–3533. [Google Scholar] [CrossRef] [PubMed]
  86. Manga, K.K.; Wang, J.; Lin, M.; Zhang, J.; Nesladek, M.; Nalla, V.; Ji, W.; Loh, K.P. High-performance broadband photodetector using solution-processible PbSe-TiO2-graphene hybrids. Adv. Mater. 2012, 24, 1697–1702. [Google Scholar] [CrossRef] [PubMed]
  87. Kamegawa, T.; Yamahana, D.; Yamashita, H. Graphene coating of TiO2 nanoparticles loaded on mesoporous silica for enhancement of photocatalytic activity. J. Phys. Chem. C 2010, 114, 15049–15053. [Google Scholar] [CrossRef]
  88. 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]
  89. Bai, S.; Wang, L.; Chen, X.; Du, J.; Xiong, Y. Chemically exfoliated metallic MoS2 nanosheets: A promising supporting co-catalyst for enhancing the photocatalytic performance of TiO2 nanocrystals. Nano Res. 2015, 8, 175–183. [Google Scholar] [CrossRef]
  90. Lang, D.; Shen, T.; Xiang, Q. Roles of MoS2 and graphene as cocatalysts in the enhanced visible-light photocatalytic H2 production activity of multiarmed CdS nanorods. ChemCatChem 2015, 7, 943–951. [Google Scholar] [CrossRef]
  91. Zhang, N.; Zhang, Y.; Pan, X.; Yang, M.Q.; Xu, Y.J. Constructing ternary CdS-graphene-TiO2 hybrids on the flatland of graphene oxide with enhanced visible-light photoactivity for selective transformation. J. Phys. Chem. C 2012, 116, 18023–18031. [Google Scholar] [CrossRef]
  92. Xiao, F.X.; Liu, B. 1D TiO2, Nanotube-Based Photocatalysts. Heterogeneous Photocatalysis. In Heterogeneous PhotoCatal; Colmenares, J.C., Xu, Y.J., Eds.; Springer: Berlin, Germany; Heidelberg, Germany, 2016; pp. 151–173. [Google Scholar]
  93. Tien, H.N.; Hur, S.H. Fabrication of 3D structured ZnO nanorod/reduced graphene oxide hydrogels and their use for photo-enhanced organic dye removal. J. Colloid Interface Sci. 2015, 437, 181–186. [Google Scholar]
  94. Agegnehu, A.K.; Pan, C.-J.; Tsai, M.-C.; Rick, J.; Su, W.-N.; Lee, J.-F.; Hwang, B.J. Visible light responsive noble metal-free nanocomposite of V-doped TiO2 nanorod with highly reduced graphene oxide for enhanced solar H2 production. Int. J. Hydrog. Energy 2016, 41, 6752–6762. [Google Scholar] [CrossRef]
  95. Utterback, J.K.; Wilker, M.B.; Brown, K.A.; King, P.W.; Eaves, J.D.; Dukovic, G. Competition between electron transfer, trapping, and recombination in CdS nanorod-hydrogenase complexes. Phys. Chem. Chem. Phys. 2015, 17, 5538–5542. [Google Scholar] [CrossRef] [PubMed]
  96. Zhang, J.; Wang, L.; Liu, X.; Li, X.A.; Huang, W. High-performance CdS-ZnS core-shell nanorod array photoelectrode for photoelectrochemical hydrogen generation. J. Mater. Chem. A 2015, 3, 535–541. [Google Scholar] [CrossRef]
  97. Liu, S.; Chen, Z.; Zhang, N.; Tang, Z.-R.; Xu, Y.J. An efficient self-assembly of CdS nanowires-reduced graphene oxide nanocomposites for selective reduction of nitro organics under visible light irradiation. J. Phys. Chem. C 2013, 117, 8251–8261. [Google Scholar] [CrossRef]
  98. Yu, J.; Jin, J.; Cheng, B.; Jaroniec, M. A noble metal-free reduced graphene oxide-CdS nanorod composite for the enhanced visible-light photocatalytic reduction of CO2 to solar fuel. J. Mater. Chem. A 2014, 2, 3407. [Google Scholar] [CrossRef]
  99. Zhang, K.; Liu, X. One step synthesis and characterization of CdS nanorod/graphene nanosheet composite. Appl. Surf. Sci. 2011, 257, 10379–10383. [Google Scholar] [CrossRef]
  100. Cao, M.; Wang, P.; Ao, Y.; Wang, C.; Hou, J.; Qian, J. Investigation on graphene and Pt co-modified CdS nanowires with enhanced photocatalytic hydrogen evolution activity under visible light irradiation. Dalton Trans. 2015, 44, 1507–1508. [Google Scholar] [CrossRef] [PubMed]
  101. Shen, S.; Ma, A.; Tang, Z.; Han, Z.; Wang, M.; Wang, Z.; Zhi, L.; Yang, J. Facile synthesis of Zn0.5Cd0.5S ultrathin nanorods on reduced graphene oxide for enhanced photocatalytic hydrogen evolution under visible light. ChemCatChem 2015, 7, 609–615. [Google Scholar] [CrossRef]
  102. Liu, J.; Bai, H.; Wang, Y.; Liu, Z.; Zhang, X.; Sun, D.D. Self-assembling TiO2, nanorods on large graphene oxide sheets at a two-phase interface and their anti-recombination in photocatalytic applications. Adv. Funct. Mater. 2010, 20, 4175–4181. [Google Scholar] [CrossRef]
  103. Liu, C.; Zhang, L.; Liu, R.; Gao, Z.; Yang, X.; Tu, Z.; Yang, F.; Ye, Z.; Cui, L.; Xu, C.; Li, Y. Hydrothermal synthesis of N-doped TiO2 nanowires and N-doped graphene heterostructures with enhanced photocatalytic properties. J. Alloys Compd. 2016, 656, 24–32. [Google Scholar] [CrossRef]
  104. Nurlaela, E.; Ouldchikh, S.; Llorens, I.; Hazemann, J.L.; Takanabe, K. Establishing efficient cobalt-based catalytic sites for oxygen evolution on a Ta3N5 photocatalyst. Chem. Mater. 2015, 27, 5685–5694. [Google Scholar] [CrossRef]
  105. Akimov, A.V.; Muckerman, J.T.; Prezhdo, O.V. Nonadiabatic dynamics of positive charge during photocatalytic water splitting on GaN (10-10) surface: charge localization governs splitting efficiency. J. Am. Chem. Soc. 2013, 135, 8682–8691. [Google Scholar] [CrossRef] [PubMed]
  106. Maeda, K.; Teramura, K.; Saito, N.; Inoue, Y.; Domen, K. Photocatalytic overall water splitting on gallium nitride powder. Bull. Chem. Soc. Jpn. 2007, 80, 1004–1010. [Google Scholar] [CrossRef]
  107. Zhang, H.; Zhao, L.; Geng, F.; Guo, L.H.; Wan, B.; Yang, Y. Carbon dots decorated graphitic carbon nitride as an efficient metal-free photocatalyst for phenol degradation. Appl. Catal. B Environ. 2016, 180, 656–662. [Google Scholar] [CrossRef]
  108. 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]
  109. Dong, G.; Zhao, K.; Zhang, L. Carbon self-doping induced high electronic conductivity and photoreactivity of g-C3N4. Chem. Commun. 2012, 48, 6178–6180. [Google Scholar] [CrossRef] [PubMed]
  110. Cao, S.; Low, J.; Yu, J.; Jaroniec, M. Polymeric photocatalysts based on graphitic carbon nitride. Adv. Mater. 2015, 27, 2150–2176. [Google Scholar] [CrossRef] [PubMed]
  111. Liu, Y.; Zhou, F.; Zhan, S.; Yang, Y.; Yin, Y. Significantly enhanced performance of g-C3N4/Bi2MoO6 films for photocatalytic degradation of pollutants under visible-light irradiation. Chem. Res. Chin. Univ. 2016, 32, 284–290. [Google Scholar] [CrossRef]
  112. Chen, Y.; Wang, B.; Lin, S.; Zhang, Y.; Wang, X. Activation of n→π* transitions in two-dimensional conjugated polymers for visible light photocatalysis. J. Phys. Chem. C 2014, 118, 29981–29989. [Google Scholar] [CrossRef]
  113. Akhundi, A.; Habibi-Yangjeh, A. A simple large-scale method for preparation of g-C3N4/SnO2 nanocomposite as visible-light-driven photocatalyst for degradation of an organic pollutant. Mater. Express 2015, 5, 309–318. [Google Scholar] [CrossRef]
  114. Chai, B.; Wang, X. Sonochemical Synthesis of CdS/C3N4 Composites with Efficient Photocatalytic Performance Under Visible Light Irradiat. J. Nanosci. Nanotechnol. 2016, 16, 2032–2041. [Google Scholar] [CrossRef] [PubMed]
  115. Chen, D.; Wang, Z.; Yue, D.; Yang, G.; Ren, T.; Ding, H. Synthesis and Visible Photodegradation Enhancement of CdS/mpg-C3N4 Photocatalyst. J. Nanosci. Nanotechnol. 2016, 16, 471–479. [Google Scholar] [CrossRef] [PubMed]
  116. Vo, V.; Van Kim, N.; Nga, N.T. V.; Trung, N.T.; Van Hanh, P.; Hoang, L.H.; Kim, S.-J. Preparation of g-C3N4/Ta2O5 Composites with Enhanced Visible-Light Photocatalytic Activity. J. Electron. Mater. 2016, 45, 2334–2340. [Google Scholar] [CrossRef]
  117. Yu, Q.; Guo, S.; Li, X.; Zhang, M. One-step fabrication and high photocatalytic activity of porous graphitic carbon nitride/graphene oxide hybrid by direct polymerization of cyanamide without templates. Russ. J. Phys. Chem. A 2014, 88, 1643–1649. [Google Scholar] [CrossRef]
  118. Xu, L.; Huang, W.Q.; Wang, L.L.; Tian, Z.A.; Hu, W.; Ma, Y.; Wang, X.; Pan, A.; Huang, G.-F. Insights into Enhanced Visible-Light Photocatalytic Hydrogen Evolution of g-C3N4 and Highly Reduced Graphene Oxide Composite: The Role of Oxygen. Chem. Mater. 2015, 27, 1612–1621. [Google Scholar] [CrossRef]
  119. Xiang, Q.; Yu, J.; Jaroniec, M. Preparation and Enhanced Visible-Light Photocatalytic H2-Production Activity of Graphene/C3N4 Composites. J. Phys. Chem. C 2011, 115, 7355–7363. [Google Scholar] [CrossRef]
  120. Tiong, P.; Lintang, H.O.; Endud, S.; Yuliati, L. Improved interfacial charge transfer and visible light activity of reduced graphene oxide–graphitic carbon nitride photocatalysts. RSC Adv. 2015, 5, 94029–94039. [Google Scholar] [CrossRef]
  121. Lee, J.S.; You, K.H.; Park, C.B. Highly photoactive, low bandgap TiO2 nanoparticles wrapped by graphene. Adv. Mater. 2012, 24, 1084–1088. [Google Scholar] [CrossRef] [PubMed]
  122. Li, Y.; Zhang, H.; Liu, P.; Wang, D.; Li, Y.; Zhao, H. Cross-linked g-C3N4/rGO nanocomposites with tunable band structure and enhanced visible light photocatalytic activity. Small 2013, 9, 3336–3344. [Google Scholar] [CrossRef] [PubMed]
  123. Park, S.; Ruoff, R.S. Chemical methods for the production of graphenes. Nat. Nanotechnol. 2009, 4, 217–224. [Google Scholar] [CrossRef] [PubMed]
  124. Dai, K.; Lu, L.; Liu, Q.; Zhu, G.; Wei, X.; Bai, J.; Xuan, L.; Wang, H. Sonication assisted preparation of graphene oxide/graphitic-C3N4 nanosheet hybrid with reinforced photocurrent for photocatalyst applications. Dalton Trans. 2014, 43, 6295–6299. [Google Scholar] [CrossRef] [PubMed]
  125. Xiang, Q.; Yu, J.; Jaroniec, M. Enhanced photocatalytic H2-production activity of graphene-modified titania nanosheets. Nanoscale 2011, 3, 3670–3678. [Google Scholar] [CrossRef] [PubMed]
  126. Ding, S.S.; Huang, W.Q.; Yang, Y.C.; Zhou, B.X.; Hu, W.Y.; Long, M.Q.; Peng, P.; Huang, G.-F. Dual role of monolayer MoS2 in enhanced photocatalytic performance of hybrid MoS2/SnO2 nanocomposite. J. Appl. Phys. 2016, 119, 205704. [Google Scholar] [CrossRef]
  127. Weng, B.; Zhang, X.; Zhang, N.; Tang, Z.R.; Xu, Y.J. Two-dimensional MoS2 nanosheet-coated Bi2S3 discoids: synthesis, formation mechanism, and photocatalytic application. Langmuir 2015, 31, 4314–4322. [Google Scholar] [CrossRef] [PubMed]
  128. Hou, Y.; Wen, Z.; Cui, S.; Guo, X.; Chen, J. Constructing 2D porous graphitic C3N4 nanosheets/nitrogen-doped graphene/layered MoS2 ternary nanojunction with enhanced photoelectrochemical activity. Adv. Mater. 2013, 25, 6291–6297. [Google Scholar] [CrossRef] [PubMed]
Figure 1. Schematic illustration of different dimensional nanocarbon co-catalysts combining with different dimensional semiconductor photocatalysts.
Figure 1. Schematic illustration of different dimensional nanocarbon co-catalysts combining with different dimensional semiconductor photocatalysts.
Catalysts 06 00111 g001
Figure 2. SEM (A) and TEM (B) images of 0D C70/0D TiO2 nanocomposites; and (C) photocatalytic performance of the as-prepared nanocomposites for degrading sulfathiazole. Reprinted with permission from [38]. Copyright 2015, Royal Society of Chemistry.
Figure 2. SEM (A) and TEM (B) images of 0D C70/0D TiO2 nanocomposites; and (C) photocatalytic performance of the as-prepared nanocomposites for degrading sulfathiazole. Reprinted with permission from [38]. Copyright 2015, Royal Society of Chemistry.
Catalysts 06 00111 g002
Figure 3. TEM (A) and HRTEM (B) images of 0D C60/1D TiO2 nanorods heterostructures; and (C) kinetics of the RhB degradation under visible irradiation with different catalyst. Without any catalyst (■), in the presence of P25 (▲), TiO2 nanorods (●), and 0D C60/1D TiO2 composites (▼) in ambient atmosphere, and 0D C60/1D TiO2 composites in N2 atmosphere (◆). Reprinted with permission from [39]. Copyright 2009, American Chemical Society.
Figure 3. TEM (A) and HRTEM (B) images of 0D C60/1D TiO2 nanorods heterostructures; and (C) kinetics of the RhB degradation under visible irradiation with different catalyst. Without any catalyst (■), in the presence of P25 (▲), TiO2 nanorods (●), and 0D C60/1D TiO2 composites (▼) in ambient atmosphere, and 0D C60/1D TiO2 composites in N2 atmosphere (◆). Reprinted with permission from [39]. Copyright 2009, American Chemical Society.
Catalysts 06 00111 g003
Figure 4. (A) Schematic illustration of photogenerated electron-hole separation mechanism in 0D C60/2D Bi2TiO4F2 heterostructure; and (B) photocatalytic performance of C60/Bi2TiO4F2 composites with different content of C60 for degrading RhB. Reprinted with permission from [41]. Copyright 2013, American Chemical Society.
Figure 4. (A) Schematic illustration of photogenerated electron-hole separation mechanism in 0D C60/2D Bi2TiO4F2 heterostructure; and (B) photocatalytic performance of C60/Bi2TiO4F2 composites with different content of C60 for degrading RhB. Reprinted with permission from [41]. Copyright 2013, American Chemical Society.
Catalysts 06 00111 g004
Figure 5. (A) HRTEM images of 1D MWCNTs/0D CdS nanocomposite; and (B) the amount of H2 evolution over different photocatalysts under visible light (λ ≥ 420 nm) and full spectrum of the Xe lamp. Reaction conditions: 35 mg of photocatalyst, 0.35 M Na2S and 0.25 M Na2SO3 as sacrificial reagents. Reprinted with permission from [51]. Copyright 2011, American Chemical Society.
Figure 5. (A) HRTEM images of 1D MWCNTs/0D CdS nanocomposite; and (B) the amount of H2 evolution over different photocatalysts under visible light (λ ≥ 420 nm) and full spectrum of the Xe lamp. Reaction conditions: 35 mg of photocatalyst, 0.35 M Na2S and 0.25 M Na2SO3 as sacrificial reagents. Reprinted with permission from [51]. Copyright 2011, American Chemical Society.
Catalysts 06 00111 g005
Figure 6. (A) Schematic illustration of photogenerated electron-hole separation and H2 evolution mechanism in 1D CNFs/2D ZnIn2S4 composites; and (B) photocatalytic performance of ZnIn2S4, CNFs, and the 1D CNFs/2D ZnIn2S4 composites with different contents of CNFs for H2 evolution from water splitting under visible light (λ ≥ 420 nm) irradiation. Reaction conditions: 30 mg of photocatalysts, 0.35 M Na2S, and 0.25 M Na2SO3 as the sacrificial reagents, and a Xe lamp as light source. Reprinted with permission from [62]. Copyright 2014, American Chemical Society.
Figure 6. (A) Schematic illustration of photogenerated electron-hole separation and H2 evolution mechanism in 1D CNFs/2D ZnIn2S4 composites; and (B) photocatalytic performance of ZnIn2S4, CNFs, and the 1D CNFs/2D ZnIn2S4 composites with different contents of CNFs for H2 evolution from water splitting under visible light (λ ≥ 420 nm) irradiation. Reaction conditions: 30 mg of photocatalysts, 0.35 M Na2S, and 0.25 M Na2SO3 as the sacrificial reagents, and a Xe lamp as light source. Reprinted with permission from [62]. Copyright 2014, American Chemical Society.
Catalysts 06 00111 g006
Figure 7. (A) Schematic illustration of the generation, transfer, and reaction of electrons in the 2D graphene/0D CdS composites under visible light irradiation; and (B) photocatalytic activity of graphene/CdS composite photocatalysts with different content of graphene. Reaction conditions: 20 mg of photocatalyst, 10 vol % lactic acid aqueous solution as a sacrificial reagent and 0.5 wt% Pt as a co-catalyst; a Xe lamp with a UV-cutoff filter (λ ≥ 420 nm) as the light source. Reprinted with permission from [78]. Copyright 2011, American Chemical Society.
Figure 7. (A) Schematic illustration of the generation, transfer, and reaction of electrons in the 2D graphene/0D CdS composites under visible light irradiation; and (B) photocatalytic activity of graphene/CdS composite photocatalysts with different content of graphene. Reaction conditions: 20 mg of photocatalyst, 10 vol % lactic acid aqueous solution as a sacrificial reagent and 0.5 wt% Pt as a co-catalyst; a Xe lamp with a UV-cutoff filter (λ ≥ 420 nm) as the light source. Reprinted with permission from [78]. Copyright 2011, American Chemical Society.
Catalysts 06 00111 g007
Figure 8. (A) TEM image of 1D ZCS/2D RGO nanocomposites; and (B) the cycling stability of ZCS and ZCS/RGO for photocatalytic H2 evolution from water splitting. Reaction conditions: 40 mg of photocatalysts, 0.02 M Na2SO3/0.1 M Na2S as sacrificial reagent with Xe lamp with a UV-cutoff filter (λ ≥ 420 nm) as light source. Reprinted with permission from [101]. Copyright 2015, Wiley-VCH.
Figure 8. (A) TEM image of 1D ZCS/2D RGO nanocomposites; and (B) the cycling stability of ZCS and ZCS/RGO for photocatalytic H2 evolution from water splitting. Reaction conditions: 40 mg of photocatalysts, 0.02 M Na2SO3/0.1 M Na2S as sacrificial reagent with Xe lamp with a UV-cutoff filter (λ ≥ 420 nm) as light source. Reprinted with permission from [101]. Copyright 2015, Wiley-VCH.
Catalysts 06 00111 g008
Figure 9. (A) Schematic illustration of the reaction process and the formation of 2D CN/2D RGO nanocomposites; (B) photocatalytic activities of the g-C3N4 and 2D CN/2D RGO photocatalysis system; and (C) recycle test of 2D CN/2D RGO nanocomposites for the degradation of RhB. Reprinted with permission from [122]. Copyright 2013, Wiley-VCH.
Figure 9. (A) Schematic illustration of the reaction process and the formation of 2D CN/2D RGO nanocomposites; (B) photocatalytic activities of the g-C3N4 and 2D CN/2D RGO photocatalysis system; and (C) recycle test of 2D CN/2D RGO nanocomposites for the degradation of RhB. Reprinted with permission from [122]. Copyright 2013, Wiley-VCH.
Catalysts 06 00111 g009
Table 1. Representative summery of photocatalysts composed of nanocarbon co-catalysts and semiconductor photocatalysts with different dimensions.
Table 1. Representative summery of photocatalysts composed of nanocarbon co-catalysts and semiconductor photocatalysts with different dimensions.
Dimension of Nanocarbons/PhotocatalystNanocarbon Co-CatalystsSemiconductor PhotocatalystsContent of Co-Catalysts (wt%)EvaluationReference
0D/0DC60TiO2-Degrade of MB[31]
C60ZnO1.5%Degrade of MB[35]
C60Cr1.3Fe0.3O33%H2 evolution rate of 220.5 μmol·h−1·g−1 (Xe lamp, λ ≥ 420 nm, 10 vol% triethanolamine as sacrificial reagent)[36]
C70TiO218%Degrade of sulfathiazole[38]
0D/1DC60TiO2 nanorods0.5%Degrade of RhB[39]
C60TiO2 nanotubes5%Degrade of organic molecule[40]
0D/2DC60Bi2TiO4F21%Degrade of RhB and EY[41]
1D/0DMWCNTsCdS10%H2 evolution rate of 174.2 μmol·h−1, (Xe lamp, λ ≥ 420 nm, 0.35 M Na2S and 0.25 M Na2SO3 as sacrificial reagent)[51]
CNTZnO60%Degrade of methyl red[52]
MWCNTsTiO2-Reduction of CO2[53]
CNTMo+TiO2-Degrade of MB[59]
1D/1DMWCNTsTiO2 nanotubes10%Degrade of RhB-6G dye[61]
1D/2DCNFsZnIn2S4 nanosheets15%H2 evolution rate of 95 μmol·h−1. (Xe lamp, λ ≥ 420 nm, 0.35 M Na2S and 0.25 M Na2SO3 as sacrificial reagent)[62]
2D/0DGrapheneCdS5%Selective oxidation of alcohols[72]
RGOCdS5%Reduction of aromatic nitro organics[71]
GOCdS5%H2 evolution rate of 314 μmol·h−1. (Xe lamp, λ ≥ 420 nm, 0.35 M Na2S and 0.25 M Na2SO3 as sacrificial reagent)[75]
GrapheneCdS cluster1%H2 evolution rate of 1.12 mmol·h−1. (Xe lamp, λ ≥ 420 nm, 10 vol % lactic acid as sacrificial reagent and 0.5 wt% Pt as a cocatalyst)[78]
N-doped GCdS2%H2 evolution rate of 210 μmol·h−1. (Xe lamp, λ ≥ 420 nm, 0.1 Na2S and 0.1 M Na2SO3 as sacrificial reagent)[79]
GrapheneTiO2-Photocurrent response.[76]
GrapheneTiO25%H2 evolution rate of 8.6 μmol·h−1. (Xe lamp, UV-vis light, 0.1 Na2S and 0.04 M Na2SO3 as sacrificial reagent)[74]
GrapheneTiO25%Selective transformation of alcohols to aldehydes[73]
N-doped GTiO25%Degrade of MO and Phenol aqueous[83]
GrapheneMoS2+TiO25%H2 evolution rate of 165.3 μmol·h−1. (Xe lamp, 25 vol % ethanol as sacrificial reagent)[88]
GrapheneMCM41+TiO20.15%Degrade of 2-propanol[87]
GrapheneCdS+TiO25%Selective oxidation of benzylic alcohols and allylic alcohols[91]
2D/1DRGOCdS nanowires5%Selective reduction of nitro organics[97]
RGOCdS nanorods0.5%Reduction of CO2[98]
RGOZn0.5Cd0.5S ultrathin nanorods2%H2 evolution rate of 30.8 μmol·h−1. (Xe lamp, λ ≥ 420 nm, 0.1 Na2S and 0.02 M Na2SO3 as sacrificial reagent)[101]
GOTiO2 nanorods-Degrade of MB[102]
RGOV-doped TiO2 nanorods10%H2 evolution rate (Xe lamp, AM 1.5 Global, 20 vol % methanol as sacrificial reagent)[94]
N-dopedGN-doped TiO2 nanowires7%Degrade of MB[103]
2D/2DRGOg-C3N40.1%Degrade of phenol[120]
RGOg-C3N42.5%Degrade of RhB and 4-nitrophenol[122]
GOg-C3N45%Degrade of MB[124]
GOg-C3N4-Degrade of MB[117]
grapheneTiO21%H2 evolution rate of 36.8 μmol·h−1. (Xe lamp, 20 mW·cm-2, 25 vol % methanol as sacrificial reagent)[125]
N-doped grapheneMoS2+g-C3N4-Degrade of MB and reduction of Cr(VI)[128]
Catalysts EISSN 2073-4344 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top