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4 pages, 519 KiB

Open AccessEditorial

Editorial: Special Issue on “Emerging Trends in TiO₂ Photocatalysis and Applications”

by Trong-On Do and Sakar Mohan

Catalysts 2020, 10(6), 670; https://doi.org/10.3390/catal10060670 - 13 Jun 2020

Cited by 10 | Viewed by 4299

Abstract

It is not an exaggerated fact that the semiconductor titanium dioxide (TiO₂) has been evolved as a prototypical material to understand the photocatalytic process and has been demonstrated for various photocatalytic applications such as pollutants degradation, water splitting, heavy metal reduction, [...] Read more.

It is not an exaggerated fact that the semiconductor titanium dioxide (TiO₂) has been evolved as a prototypical material to understand the photocatalytic process and has been demonstrated for various photocatalytic applications such as pollutants degradation, water splitting, heavy metal reduction, CO₂ conversion, N₂ fixation, bacterial disinfection, etc [...] Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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Research

Jump to: Editorial, Review

11 pages, 3178 KiB

Open AccessCommunication

Facile Formation of Anatase Nanoparticles on H-Titanate Nanotubes at Low Temperature for Efficient Visible Light-Driven Degradation of Organic Pollutants

by Weiwei Fu, Zhiqiang Shi, Helong Bai, Jinyu Dai, Zhiming Lu, Feifei Lei, Deguang Zhang, Lun Zhao and Zongtao Zhang

Catalysts 2020, 10(6), 695; https://doi.org/10.3390/catal10060695 - 19 Jun 2020

Cited by 3 | Viewed by 3063

Abstract

Anatase nanoparticles (5–10 nm) generated on H-titanate nanotube surface (H-titanate/anatase) were prepared by an ingenious and simple method. H-titanate tubes were prepared by a hydrothermal reaction of Ti powder in concentrated NaOH solution and an ion exchange process with HNO₃ solution. After [...] Read more.

Anatase nanoparticles (5–10 nm) generated on H-titanate nanotube surface (H-titanate/anatase) were prepared by an ingenious and simple method. H-titanate tubes were prepared by a hydrothermal reaction of Ti powder in concentrated NaOH solution and an ion exchange process with HNO₃ solution. After that, at a relatively low drying temperature (100 °C), a small quantity of anatase nanoparticles were in-situ formed on the H-titanate tubes surface by a surface dehydration reaction. In-situ transformation can form a strong interface coupling between H-titanate and anatase, which is conducive to accelerating charge transfer and improving its photocatalytic activity. In addition, the smaller average crystal size, the large specific surface areas (BET), the nanotubed and layered structure and the synergistic effect of dual phases would be beneficial to improving the photocatalytic efficiency. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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15 pages, 5399 KiB

Open AccessArticle

Controllable Fabrication of Heterogeneous p-TiO₂ QDs@g-C₃N₄ p-n Junction for Efficient Photocatalysis

by Songbo Wang, Feifan Wang, Zhiming Su, Xiaoning Wang, Yicheng Han, Lei Zhang, Jun Xiang, Wei Du and Na Tang

Catalysts 2019, 9(5), 439; https://doi.org/10.3390/catal9050439 - 10 May 2019

Cited by 34 | Viewed by 4691

Abstract

Photocatalytic technology has been considered to be an ideal approach to solve the energy and environmental crises, and TiO₂ is regarded as the most promising photocatalyst. Compared with bare TiO₂, TiO₂ based p-n heterojunction exhibits a much better performance [...] Read more.

Photocatalytic technology has been considered to be an ideal approach to solve the energy and environmental crises, and TiO₂ is regarded as the most promising photocatalyst. Compared with bare TiO₂, TiO₂ based p-n heterojunction exhibits a much better performance in charge separation, light absorption and photocatalytic activity. Herein, we developed an efficient method to prepare p-type TiO₂ quantum dots (QDs) and decorated graphitic carbonitrile (g-C₃N₄) nanocomposites, while the composition and structure of the TiO₂@g-C₃N₄ were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-visible diffuse reflectance spectroscopy characterizations. The characterization results reveal the surface decorated TiO₂ quantum dots is decomposed by titanium glycerolate, which exhibits p-type conductivity. The presence of p-n heterojunction over interface is confirmed, and photoluminescence results indicate a better performance in transfer and separation of photo-generated charge carriers than pure semiconductors and type-II heterojunction. Moreover, the synergy of p-n heterojunction over interface, strong interface interaction, and quantum-size effect significantly contributes to the promoted performance of TiO₂ QDs@g-C₃N₄ composites. As a result, the as-fabricated TiO₂ QDs@g-C₃N₄ composite with a p/n mass ratio of 0.15 exhibits improved photo-reactivity of 4.3-fold and 5.4-fold compared to pure g-C₃N₄ in degradation of organic pollutant under full solar spectrum and visible light irradiation, respectively. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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10 pages, 5254 KiB

Open AccessArticle

Improvement of the Photoelectrochemical Performance of TiO₂ Nanorod Array by PEDOT and Oxygen Vacancy Co-Modification

by Bin Yang, Guoqiang Chen, Huiwen Tian and Lei Wen

Catalysts 2019, 9(5), 407; https://doi.org/10.3390/catal9050407 - 30 Apr 2019

Cited by 7 | Viewed by 3348

Abstract

In this study, oxygen vacancy modified TiO₂ nanorod array photoelectrode was prepared by reducing hydrogen atmosphere to increase its free charge carrier density. Subsequently, a p-type conductive poly 3,4-ethylenedioxythiophene (PEDOT) layer was deposited on the surface of oxygen vacancy modified TiO₂ [...] Read more.

In this study, oxygen vacancy modified TiO₂ nanorod array photoelectrode was prepared by reducing hydrogen atmosphere to increase its free charge carrier density. Subsequently, a p-type conductive poly 3,4-ethylenedioxythiophene (PEDOT) layer was deposited on the surface of oxygen vacancy modified TiO₂, to inhibit the surface states. Meanwhile, a p-n heterojunction formed between PEDOT and TiO₂ to improve the separation of photo-induced carriers further. The photocurrent of TiO₂ nanorod array increased to nearly 0.9 mA/cm² after the co-modification under standard sunlight illumination, whose value is nearly nine times higher than that of pure TiO₂ nanorod array. Thus, this is a promising modification method for TiO₂ photoanode photoelectrochemical (PEC) performance improving. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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19 pages, 2205 KiB

Open AccessArticle

Optimization of Photocatalytic Degradation of Acid Blue 113 and Acid Red 88 Textile Dyes in a UV-C/TiO₂ Suspension System: Application of Response Surface Methodology (RSM)

by Soroosh Mortazavian, Ali Saber and David E. James

Catalysts 2019, 9(4), 360; https://doi.org/10.3390/catal9040360 - 14 Apr 2019

Cited by 115 | Viewed by 8123

Abstract

Textile industries produce copious amounts of colored wastewater some of which are toxic to humans and aquatic biota. This study investigates optimization of a bench-scale UV-C photocatalytic process using a TiO₂ catalyst suspension for degradation of two textile dyes, Acid Blue 113 [...] Read more.

Textile industries produce copious amounts of colored wastewater some of which are toxic to humans and aquatic biota. This study investigates optimization of a bench-scale UV-C photocatalytic process using a TiO₂ catalyst suspension for degradation of two textile dyes, Acid Blue 113 (AB 113) and Acid Red 88 (AR 88). From preliminary experiments, appropriate ranges for experimental factors including reaction time, solution pH, initial dye concentration and catalyst dose, were determined for each dye. Response surface methodology (RSM) using a cubic IV optimal design was then used to design the experiments and optimize the process. Analysis of variance (ANOVA) was employed to determine significance of experimental factors and their interactions. Results revealed that among the studied factors, solution pH and initial dye concentration had the strongest effects on degradation rates of AB 113 and AR 88, respectively. Least-squares cubic regression models were generated by step-wise elimination of non-significant (p-value > 0.05) terms from the proposed model. Under optimum treatment conditions, removal efficiencies reached 98.7% for AB 113 and 99.6% for AR 88. Kinetic studies showed that a first-order kinetic model could best describe degradation data for both dyes, with degradation rate constants of k_{1, AB 113} = 0.048 min⁻¹ and k_{1, AR 88} = 0.059 min⁻¹. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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15 pages, 3103 KiB

Open AccessArticle

Facet-Dependent Interfacial Charge Transfer in TiO₂/Nitrogen-Doped Graphene Quantum Dots Heterojunctions for Visible-Light Driven Photocatalysis

by Nan-Quan Ou, Hui-Jun Li, Bo-Wen Lyu, Bo-Jie Gui, Xiong Sun, Dong-Jin Qian, Yanlin Jia, Xianying Wang and Junhe Yang

Catalysts 2019, 9(4), 345; https://doi.org/10.3390/catal9040345 - 9 Apr 2019

Cited by 46 | Viewed by 5027

Abstract

Interfacial charge transfer is crucial in the efficient conversion of solar energy into fuels and electricity. In this paper, heterojunction composites were fabricated, comprised of anatase TiO₂ with different percentages of exposed {101} and {001} facets and nitrogen-doped quantum dots (NGQDs) to [...] Read more.

Interfacial charge transfer is crucial in the efficient conversion of solar energy into fuels and electricity. In this paper, heterojunction composites were fabricated, comprised of anatase TiO₂ with different percentages of exposed {101} and {001} facets and nitrogen-doped quantum dots (NGQDs) to enhance the transfer efficiency of photo-excited charge carriers. The photocatalytic performances of all samples were evaluated for RhB degradation under visible light irradiation, and the hybrid containing TiO₂ with 56% {001} facets demonstrated the best photocatalytic activity. The excellent photoactivity of TiO₂/NGQDs was owed to the synergistic effects of the following factors: (i) The unique chemical features of NGQDs endowed NGQDs with high electronic conductivities and provided its direct contact with the TiO₂ surface via forming Ti–O–C chemical bonds. (ii) The co-exposed {101} and {001} facets were beneficial for the separation and transfer of charge carriers in anatase TiO₂. (iii) The donor-acceptor interaction between NGQDs and electron-rich {101} facets of TiO₂ could remarkably enhance the photocurrent, thus hindering the charge carriers recombination rate. Extensive characterization of their physiochemical properties further showed the synergistic effect of facet-manipulated electron-hole separation in TiO₂ and donor-acceptor interaction in graphene quantum dots (GQDs)/TiO₂ on photocatalytic activity. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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12 pages, 1750 KiB

Open AccessArticle

Hydrogen Production from Glycerol Photoreforming on TiO₂/HKUST-1 Composites: Effect of Preparation Method

by Fabián M. Martínez, Elim Albiter, Salvador Alfaro, Ana L. Luna, Christophe Colbeau-Justin, José M. Barrera-Andrade, Hynd Remita and Miguel A. Valenzuela

Catalysts 2019, 9(4), 338; https://doi.org/10.3390/catal9040338 - 4 Apr 2019

Cited by 25 | Viewed by 5616

Abstract

Coupling metal-organic frameworks (MOFs) with inorganic semiconductors has been successfully tested in a variety of photocatalytic reactions. In this work we present the synthesis of TiO₂/HKUST-1 composites by grinding, solvothermal, and chemical methods, using different TiO₂ loadings. These composites were [...] Read more.

Coupling metal-organic frameworks (MOFs) with inorganic semiconductors has been successfully tested in a variety of photocatalytic reactions. In this work we present the synthesis of TiO₂/HKUST-1 composites by grinding, solvothermal, and chemical methods, using different TiO₂ loadings. These composites were used as photocatalysts for hydrogen production by the photoreforming of a glycerol-water mixture under simulated solar light. Several characterization techniques were employed, including X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), infrared spectroscopy (FTIR), and time-resolved microwave conductivity (TRMC). A synergetic effect was observed with all TiO₂/HKUST-1 composites (mass ratio TiO₂/MOF 1:1), which presented higher photocatalytic activity than that of individual components. These results were explained in terms of an inhibition of the charge carrier (hole-electron) recombination reaction after photoexcitation, favoring the electron transfer from TiO₂ to the MOF and creating reversible Cu¹⁺/Cu⁰ entities useful for hydrogen production. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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13 pages, 2279 KiB

Open AccessArticle

Synergistic Effect of Photocatalytic Degradation of Hexabromocyclododecane in Water by UV/TiO₂/persulfate

by Qiang Li, Lifang Wang, Xuhui Fang, Li Zhang, Jingjiu Li and Hongyong Xie

Catalysts 2019, 9(2), 189; https://doi.org/10.3390/catal9020189 - 18 Feb 2019

Cited by 33 | Viewed by 4554

Abstract

In this work, the elimination of hexabromocyclododecane (HBCD) is explored by using photodegradation of the UV/TiO₂ system, the UV/potassium persulfate (KPS) system, and the homo/heterogeneous UV/TiO₂/KPS system. The experimental results show that the dosages of TiO₂ and potassium persulfate [...] Read more.

In this work, the elimination of hexabromocyclododecane (HBCD) is explored by using photodegradation of the UV/TiO₂ system, the UV/potassium persulfate (KPS) system, and the homo/heterogeneous UV/TiO₂/KPS system. The experimental results show that the dosages of TiO₂ and potassium persulfate have optimum values to increase the degradation degree. HBCD can be almost completely degraded and 74.3% of the total bromine content is achieved in the UV/TiO₂/KPS homo/heterogeneous photocatalysis, much more than in the UV/persulfate system and the UV/TiO₂ system. Roles of radicals SO₄^•− and OH^• in the photocatalysis systems are discussed based on experimental measurements. The high yield of the concentration of bromide ions and decreased pH value indicates that synergistic effects exist in the UV/TiO₂/KPS homo/heterogeneous photocatalysis, which can mineralize HBCD into inorganic small molecules like carboxylic acids, CO₂ and H₂O, thus much less intermediates are formed. The possible pathways of degradation of HBCD in the UV/TiO₂/KPS system were also analyzed by GC/MS. This work will have practical application potential in the fields of pollution control and environmental management. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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10 pages, 1099 KiB

Open AccessArticle

Photocatalytic Degradation of Microcystins by TiO₂ Using UV-LED Controlled Periodic Illumination

by Olivia M. Schneider, Robert Liang, Leslie Bragg, Ivana Jaciw-Zurakowsky, Azar Fattahi, Shasvat Rathod, Peng Peng, Mark R. Servos and Y. Norman Zhou

Catalysts 2019, 9(2), 181; https://doi.org/10.3390/catal9020181 - 14 Feb 2019

Cited by 27 | Viewed by 5859

Abstract

Toxic microcystins (MCs) produced by freshwater cyanobacteria such as Microcystis aeruginosa are of concern because of their negative health and economic impacts globally. An advanced oxidation process using UV/TiO₂ offers a promising treatment option for hazardous organic pollutants such as microcystins. The [...] Read more.

Toxic microcystins (MCs) produced by freshwater cyanobacteria such as Microcystis aeruginosa are of concern because of their negative health and economic impacts globally. An advanced oxidation process using UV/TiO₂ offers a promising treatment option for hazardous organic pollutants such as microcystins. The following work details the successful degradation of MC-LA, MC-LR, and MC-RR using a porous titanium–titanium dioxide (PTT) membrane under UV-LED light. Microcystin quantitation was achieved by sample concentration and subsequent LC–MS/MS analysis. The PTT membrane offers a treatment option that eliminates the need for the additional filtration or separation steps required for traditional catalysts. Controlled periodic illumination was successfully used to decrease the total light exposure time and improve the photonic efficiency for a more cost-effective treatment system. Individual degradation rates were influenced by electrostatic forces between the catalyst and differently charged microcystins, which can potentially be adjusted by modifying the solution pH and the catalyst’s isoelectric point. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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15 pages, 4419 KiB

Open AccessArticle

Development of TiO₂-Carbon Composite Acid Catalyst for Dehydration of Fructose to 5-Hydroxymethylfurfural

by Morongwa Martha Songo, Richard Moutloali and Suprakas Sinha Ray

Catalysts 2019, 9(2), 126; https://doi.org/10.3390/catal9020126 - 31 Jan 2019

Cited by 23 | Viewed by 3667

Abstract

A TiO₂-Carbon (TiO₂C) composite was prepared using the microwave-assisted method and sulfonated using fuming sulfuric acid to produce a TiO₂C solid acid catalyst. The prepared solid acid catalyst was characterised using scanning electron microscopy, Brunauer-Emmett-Teller analysis, Fourier [...] Read more.

A TiO₂-Carbon (TiO₂C) composite was prepared using the microwave-assisted method and sulfonated using fuming sulfuric acid to produce a TiO₂C solid acid catalyst. The prepared solid acid catalyst was characterised using scanning electron microscopy, Brunauer-Emmett-Teller analysis, Fourier transform infrared spectroscopy, and X-ray diffraction. Crystallinity analysis confirmed that TiO₂C has an anatase structure, while analysis of its morphology showed a combination of spheres and particles with a diameter of 50 nm. The TiO₂C solid acid catalyst was tested for use in the catalytic dehydration of fructose to 5-hydroxymethylfurfural (5-HMF). The effect of reaction time, reaction temperature, catalyst dosage, and solvent were investigated against the 5-HMF yield. The 5-HMF yield was found to be 90% under optimum conditions. The solid acid catalyst is very stable and can be reused for four catalytic cycles. Hence, the material has great potential for use in industrial applications and can be used for the direct conversion of fructose to 5-HMF because of its high activity and high reusability. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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10 pages, 3240 KiB

Open AccessArticle

Bleached Wood Supports for Floatable, Recyclable, and Efficient Three Dimensional Photocatalyst

by Yuming He, Huayang Li, Xuelian Guo and Rongbo Zheng

Catalysts 2019, 9(2), 115; https://doi.org/10.3390/catal9020115 - 26 Jan 2019

Cited by 13 | Viewed by 3069

Abstract

To suppress the agglomeration of a photocatalyst, facilitate its recovery, and avoid photolysis of dyes, various support materials such as ceramic, carbon, and polymer have been investigated. However, these support materials pose the following additional challenges: ceramic supports will settle down at the [...] Read more.

To suppress the agglomeration of a photocatalyst, facilitate its recovery, and avoid photolysis of dyes, various support materials such as ceramic, carbon, and polymer have been investigated. However, these support materials pose the following additional challenges: ceramic supports will settle down at the bottom of their container due to their high density, while the carbon support will absorb the UV-vis light for its black color. Herein, we propose a floatable, UV transmitting, mesoporous bleached wood with most lignin removal to support P25 nanoparticles (BP-wood) that can effectively, recyclable, three dimensional (3D) photocatalytic degrade dyes such as methylene blue (MB) under ambient sunlight. The BP-wood has the following advantages: (1) The delignification makes the BP-wood more porous to not only quickly transport MB solutions upstream to the top surface, but is also decorated with P25 nanoparticles on the cell wall to form a 3D photocatalyst. (2) The delignification endows the BP-wood with good UV transmittance to undergo 3D photocatalytic degradation under sunlight. (3) It can float on the surface of the MB solution to capture more sunlight to enhance the photodegradation efficiency by suppressing the photolysis of MB. (4) It has comparable or even better photocatalytic degradation of 40 mg/L and 60 mg/L MB than that of P25 nanoparticles suspension. (5) It is green, recyclable, and scalable. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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15 pages, 4504 KiB

Open AccessArticle

Ru-Ti Oxide Based Catalysts for HCl Oxidation: The Favorable Oxygen Species and Influence of Ce Additive

by Jian Shi, Feng Hui, Jun Yuan, Qinwei Yu, Suning Mei, Qian Zhang, Jialin Li, Weiqiang Wang, Jianming Yang and Jian Lu

Catalysts 2019, 9(2), 108; https://doi.org/10.3390/catal9020108 - 22 Jan 2019

Cited by 36 | Viewed by 5093

Abstract

Several Ru-Ti oxide-based catalysts were investigated for the catalytic oxidation of HCl to Cl₂ in this work. The active component RuO₂ was loaded on different titanium-containing supports by a facile wetness impregnation method. The Ru-Ti oxide based catalysts were characterized by [...] Read more.

Several Ru-Ti oxide-based catalysts were investigated for the catalytic oxidation of HCl to Cl₂ in this work. The active component RuO₂ was loaded on different titanium-containing supports by a facile wetness impregnation method. The Ru-Ti oxide based catalysts were characterized by XRD, N₂ sorption, SEM, TEM, H₂-TPR, XPS, and Raman, which is correlated with the catalytic tests. Rutile TiO₂ was confirmed as the optimal support even though it has a low specific surface area. In addition to the interfacial epitaxial lattice matching and epitaxy, the extraordinary performance of Ru-Ti rutile oxide could also be attributed to the favorable oxygen species on Ru sites and specific active phase-support interactions. On the other hand, the influence of additive Ce on the RuO₂/TiO₂-rutile was studied. The incorporation of Ce by varied methods resulted in further oxidation of RuO₂ into RuO₂^δ+ and a modification of the support structure. The amount of favorable oxygen species on the surface was decreased. As a result, the Deacon activity was lowered. It was demonstrated that the surface oxygen species and specific interactions of the Ru-Ti rutile oxide were critical to HCl oxidation. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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16 pages, 3739 KiB

Open AccessArticle

Adsorption and Photocatalytic Decomposition of Gaseous 2-Propanol Using TiO₂-Coated Porous Glass Fiber Cloth

by Sayaka Yanagida, Kentaro Hirayama, Kenichiro Iwasaki and Atsuo Yasumori

Catalysts 2019, 9(1), 82; https://doi.org/10.3390/catal9010082 - 14 Jan 2019

Cited by 10 | Viewed by 4696

Abstract

Combinations of TiO₂ photocatalysts and various adsorbents have been extensively investigated for eliminating volatile organic compounds (VOCs) at low concentrations. Herein, TiO₂ and porous glass cloth composites were prepared by acid leaching and subsequent TiO₂ dip-coating of the electrically applied [...] Read more.

Combinations of TiO₂ photocatalysts and various adsorbents have been extensively investigated for eliminating volatile organic compounds (VOCs) at low concentrations. Herein, TiO₂ and porous glass cloth composites were prepared by acid leaching and subsequent TiO₂ dip-coating of the electrically applied glass (E-glass) cloth, and its adsorption and photocatalytic ability were investigated. Acid leaching increased the specific surface area of the E-glass cloth from 1 to 430 m²/g while maintaining sufficient mechanical strength for supporting TiO₂. Further, the specific surface area remained large (290 m²/g) after TiO₂ coating. In the photocatalytic decomposition of gaseous 2-propanol, the TiO₂-coated porous glass cloth exhibited higher adsorption and photocatalytic decomposition ability than those exhibited by the TiO₂-coated, non-porous glass cloth. The porous composite limited desorption of acetone, which is a decomposition intermediate of 2-propanol, until 2-propanol was completely decomposed to CO₂. The CO₂ generation rate was affected by the temperature condition (15 or 35 °C) and the water content (2 or 18 mg/L); the latter also influenced 2-propanol adsorption in photocatalytic decomposition. Both the conditions may change the diffusion and adsorption behavior of 2-propanol in the porous composite. As demonstrated by its high adsorption and photocatalytic ability, the composite (TiO₂ and porous glass cloth) effectively eliminates VOCs, while decreasing the emission of harmful intermediates. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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12 pages, 3115 KiB

Open AccessArticle

Enhanced Photocatalytic Reduction of Cr(VI) by Combined Magnetic TiO₂-Based NFs and Ammonium Oxalate Hole Scavengers

by Yin-Hsuan Chang and Ming-Chung Wu

Catalysts 2019, 9(1), 72; https://doi.org/10.3390/catal9010072 - 10 Jan 2019

Cited by 27 | Viewed by 5699

Abstract

Heavy metal pollution of wastewater with coexisting organic contaminants has become a serious threat to human survival and development. In particular, hexavalent chromium, which is released into industrial wastewater, is both toxic and carcinogenic. TiO₂ photocatalysts have attracted much attention due to [...] Read more.

Heavy metal pollution of wastewater with coexisting organic contaminants has become a serious threat to human survival and development. In particular, hexavalent chromium, which is released into industrial wastewater, is both toxic and carcinogenic. TiO₂ photocatalysts have attracted much attention due to their potential photodegradation and photoreduction abilities. Though TiO₂ demonstrates high photocatalytic performance, it is a difficult material to recycle after the photocatalytic reaction. Considering the secondary pollution caused by the photocatalysts, in this study we prepared Ag/Fe₃O₄/TiO₂ nanofibers (NFs) that could be magnetically separated using hydrothermal synthesis, which was considered a benign and effective resolution. For the photocatalytic test, the removal of Cr(VI) was carried out by Ag/Fe₃O₄/TiO₂ nanofibers combined with ammonium oxalate (AO). AO acted as a hole scavenger to enhance the electron-hole separation ability, thereby dramatically enhancing the photoreduction efficiency of Cr(VI). The reaction rate constant for Ag/Fe₃O₄/TiO₂ NFs in the binary system reached 0.260 min⁻¹, 6.95 times of that of Ag/Fe₃O₄/TiO₂ NFs in a single system (0.038 min⁻¹). The optimized Ag/Fe₃O₄/TiO₂ NFs exhibited high efficiency and maintained their photoreduction efficiency at 90% with a recyclability of 87% after five cycles. Hence, taking into account the high magnetic separation behavior, Ag/Fe₃O₄/TiO₂ NFs with a high recycling capability are a potential photocatalyst for wastewater treatment. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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22 pages, 6068 KiB

Open AccessArticle

Photocatalytic Hydrogen Production Under Near-UV Using Pd-Doped Mesoporous TiO₂ and Ethanol as Organic Scavenger

by Bianca Rusinque, Salvador Escobedo and Hugo de Lasa

Catalysts 2019, 9(1), 33; https://doi.org/10.3390/catal9010033 - 2 Jan 2019

Cited by 21 | Viewed by 6874

Abstract

Photocatalysis can be used advantageously for hydrogen production using a light source (near-UV light), a noble metal-doped semiconductor and an organic scavenger (2.0 v/v% ethanol). With this end, palladium was doped on TiO₂ photocatalysts at different metal loadings (0.25 to 5.00 wt%). [...] Read more.

Photocatalysis can be used advantageously for hydrogen production using a light source (near-UV light), a noble metal-doped semiconductor and an organic scavenger (2.0 v/v% ethanol). With this end, palladium was doped on TiO₂ photocatalysts at different metal loadings (0.25 to 5.00 wt%). Photocatalysts were synthetized using a sol-gel method enhancing morphological properties with a soft template precursor. Experiments were carried out in the Photo-CREC Water II reactor system developed at CREC-UWO (Chemical Reactor Engineering Centre- The University of Western Ontario) Canada. This novel unit offers hydrogen storage and symmetrical irradiation allowing precise irradiation measurements for macroscopic energy balances. Hydrogen production rates followed in all cases a zero-order reaction, with quantum yields as high as 30.8%. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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12 pages, 2884 KiB

Open AccessArticle

Comparing the Efficiency of N-Doped TiO₂ and N-Doped Bi₂MoO₆ Photo Catalysts for MB and Lignin Photodegradation

by Ricardo Rangel, Verónica Janneth Cedeño, Jaime Espino, Pascual Bartolo-Pérez, Geonel Rodríguez-Gattorno and Juan José Alvarado-Gil

Catalysts 2018, 8(12), 668; https://doi.org/10.3390/catal8120668 - 19 Dec 2018

Cited by 30 | Viewed by 5765

Abstract

In this study, we tested the efficiency of nitrogen-doped titanium dioxide (N-TiO₂) and nitrogen-doped bismuth molybdate (N-Bi₂MoO₆) compounds as photocatalysts capable of degrading methylene blue and lignin molecules under irradiation with ultraviolet (UV) and visible light (VIS). [...] Read more.

In this study, we tested the efficiency of nitrogen-doped titanium dioxide (N-TiO₂) and nitrogen-doped bismuth molybdate (N-Bi₂MoO₆) compounds as photocatalysts capable of degrading methylene blue and lignin molecules under irradiation with ultraviolet (UV) and visible light (VIS). Moreover, we compared TiO₂ and Bi₂MoO₆ catalysts with N-TiO₂ and N-Bi₂MoO₆ compounds using chemical coprecipitation. The catalysts were prepared starting from Ti(OCH₂CH₂CH₃)₄, Bi(NO₃)₃·5H₂O, and (NH₄)₆Mo₇O₂₄ reagents. N-doping was achieved in a continuous reflux system, using ethylene diamine as a nitrogen source. The resulting materials were characterized using Scanning Electron Microscopy (SEM), X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Additionally, we observed the decrease in particle size after processing the compounds in the reflux system. The results regarding photocatalytic degradation tests show a remarkable effect for nitrogen doped samples, achieving 90% of lignin degradation. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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12 pages, 2523 KiB

Open AccessArticle

Highly Selective Photocatalytic Reduction of o-Dinitrobenzene to o-Phenylenediamine over Non-Metal-Doped TiO₂ under Simulated Solar Light Irradiation

by Hamza M. El-Hosainy, Said M. El-Sheikh, Adel A. Ismail, Amer Hakki, Ralf Dillert, Hamada M. Killa, Ibrahim A. Ibrahim and Detelf W. Bahnemann

Catalysts 2018, 8(12), 641; https://doi.org/10.3390/catal8120641 - 9 Dec 2018

Cited by 12 | Viewed by 5944

Abstract

Photocatalytic reduction and hydrogenation reaction of o-dinitrobenzene in the presence of oxalic acid over anatase-brookite biphasic TiO₂ and non-metal-doped anatase-brookite biphasic TiO₂ photocatalysts under solar simulated light was investigated. Compared with commercial P25 TiO₂, the prepared un-doped and doped [...] Read more.

Photocatalytic reduction and hydrogenation reaction of o-dinitrobenzene in the presence of oxalic acid over anatase-brookite biphasic TiO₂ and non-metal-doped anatase-brookite biphasic TiO₂ photocatalysts under solar simulated light was investigated. Compared with commercial P25 TiO₂, the prepared un-doped and doped anatase-brookite biphasic TiO₂ exhibited a high selectivity towards the formation of o-nitroaniline (85.5%) and o-phenylenediamine ~97%, respectively. The doped anatase-brookite biphasic TiO₂ has promoted photocatalytic reduction of the two-nitro groups of o-dinitrobenzene to the corresponding o-phenylenediamine with very high yield ~97%. Electron paramagnetic resonance analysis, Transient Absorption Spectroscopy (TAS) and Photoluminescence analysis (PL) were performed to determine the distribution of defects and the fluorescence lifetime of the charge carriers for un-doped and doped photocatalysts. The superiority of the doped TiO₂ photocatalysts is accredited to the creation of new dopants (C, N, and S) as hole traps, the formation of long-lived Ti³⁺ defects which leads to an increase in the fluorescence lifetime of the formed charge carriers. The schematic diagram of the photocatalytic reduction of o-dinitrobenzene using the doped TiO₂ under solar light was also illustrated in detail. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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20 pages, 4471 KiB

Open AccessArticle

Enhanced Photocatalytic Activity of Titania by Co-Doping with Mo and W

by Osmín Avilés-García, Jaime Espino-Valencia, Rubí Romero-Romero, José Luis Rico-Cerda, Manuel Arroyo-Albiter, Dora Alicia Solís-Casados and Reyna Natividad-Rangel

Catalysts 2018, 8(12), 631; https://doi.org/10.3390/catal8120631 - 6 Dec 2018

Cited by 45 | Viewed by 5894

Abstract

Various W and Mo co-doped titanium dioxide (TiO₂) materials were obtained through the EISA (Evaporation-Induced Self-Assembly) method and then tested as photocatalysts in the degradation of 4-chlorophenol. The synthesized materials were characterized by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, [...] Read more.

Various W and Mo co-doped titanium dioxide (TiO₂) materials were obtained through the EISA (Evaporation-Induced Self-Assembly) method and then tested as photocatalysts in the degradation of 4-chlorophenol. The synthesized materials were characterized by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman spectroscopy (RS), N₂ physisorption, UV-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The results showed that the W-Mo-TiO₂ catalysts have a high surface area of about 191 m²/g, and the presence of an anatase crystalline phase. The co-doped materials exhibited smaller crystallite sizes than those with one dopant, since the crystallinity is inhibited by the presence of both species. In addition, tungsten and molybdenum dopants are distributed and are incorporated into the anatase structure of TiO₂, due to changes in red parameters and lattice expansion. Under our experimental conditions, the co-doped TiO₂ catalyst presented 46% more 4-chlorophenol degradation than Degussa P25. The incorporation of two dopant cations in titania improved its photocatalytic performance, which was attributed to a cooperative effect by decreasing the recombination of photogenerated charges, high radiation absorption capacity, high surface areas, and low crystallinity. When TiO₂ is co-doped with the same amount of both cations (1 wt.%), the highest degradation and mineralization (97% and 74%, respectively) is achieved. Quinones were the main intermediates in the 4-chlorophenol oxidation by W-Mo-TiO₂ and 1,2,4-benzenetriol was incompletely degraded. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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24 pages, 19869 KiB

Open AccessArticle

Photocatalytic Degradation of Estriol Using Iron-Doped TiO₂ under High and Low UV Irradiation

by Irwing M. Ramírez-Sánchez and Erick R. Bandala

Catalysts 2018, 8(12), 625; https://doi.org/10.3390/catal8120625 - 5 Dec 2018

Cited by 32 | Viewed by 5420

Abstract

Iron-doped TiO₂ nanoparticles (Fe-TiO₂) were synthesized and photocatalitically investigated under high and low fluence values of UV radiation. The Fe-TiO₂ physical characterization was performed using X-ray Powder Diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, Transmission Electron Microscopy (TEM), Scanning [...] Read more.

Iron-doped TiO₂ nanoparticles (Fe-TiO₂) were synthesized and photocatalitically investigated under high and low fluence values of UV radiation. The Fe-TiO₂ physical characterization was performed using X-ray Powder Diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Diffuse Reflectance Spectroscopy (DRS), and X-ray Photoelectron Spectroscopy (XPS). The XPS evidenced that the ferric ion (Fe³⁺) was in the TiO₂ lattice and unintentionally added co-dopants were also present because of the precursors of the synthetic method. The Fe³⁺ concentration played a key role in the photocatalytic generation of hydroxyl radicals (^•OH) and estriol (E3) degradation. Fe-TiO₂ accomplished E3 degradation, and it was found that the catalyst with 0.3 at.% content of Fe (0.3 Fe-TiO₂) enhanced the photocatalytic activity under low UV irradiation compared with TiO₂ without intentionally added Fe (zero-iron TiO₂) and Aeroxide^® TiO₂ P25. Furthermore, the enhanced photocatalytic activity of 0.3 Fe-TiO₂ under low UV irradiation may have applications when radiation intensity must be controlled, as in medical applications, or when strong UV absorbing species are present in water. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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15 pages, 3061 KiB

Open AccessFeature PaperArticle

Mechanistic Study on Facet-Dependent Deposition of Metal Nanoparticles on Decahedral-Shaped Anatase Titania Photocatalyst Particles

by Kenta Kobayashi, Mai Takashima, Mai Takase and Bunsho Ohtani

Catalysts 2018, 8(11), 542; https://doi.org/10.3390/catal8110542 - 13 Nov 2018

Cited by 12 | Viewed by 4723

Abstract

Facet-selective gold or platinum-nanoparticle deposition on decahedral-shaped anatase titania particles (DAPs) exposing {001} and {101} facets via photodeposition (PD) from metal-complex sources was reexamined using DAPs prepared with gas-phase reaction of titanium (IV) chloride and oxygen by quantitatively evaluating the area deposition density [...] Read more.

Facet-selective gold or platinum-nanoparticle deposition on decahedral-shaped anatase titania particles (DAPs) exposing {001} and {101} facets via photodeposition (PD) from metal-complex sources was reexamined using DAPs prepared with gas-phase reaction of titanium (IV) chloride and oxygen by quantitatively evaluating the area deposition density on {001} and {101} and comparing with the results of deposition from colloidal metal particles in the dark (CDD) or under photoirradiation (CDL). The observed facet selectivity, more or less {101} preferable, depended mainly on pH of the reaction suspensions and was almost non-selective at low pH regardless of the deposition method, PD or CDL, and the metal-source materials. Based on the results, the present authors propose that facet selectivity is attributable to surface charges (zeta potential) depending on the kind of facets, {001} and {101}, and pH of the reaction mixture and that this concept can explain the observed facet selectivity and possibly the reported facet selectivity without taking into account facet-selective reaction of photoexcited electrons and positive holes on {101} and {001} facets, respectively. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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7 pages, 3117 KiB

Open AccessArticle

Solid-Phase Photocatalytic Degradation of Polyvinyl Borate

by Hafize Nagehan Koysuren

Catalysts 2018, 8(11), 499; https://doi.org/10.3390/catal8110499 - 26 Oct 2018

Cited by 10 | Viewed by 3170

Abstract

In this study, polymer composites based on polyvinyl borate (PVB) with titanium dioxide (TiO₂) nanoparticles were prepared through the condensation reaction of polyvinyl alcohol and boric acid in the presence of TiO₂ nanoparticles. The solid-phase photocatalytic degradation of the polymer [...] Read more.

In this study, polymer composites based on polyvinyl borate (PVB) with titanium dioxide (TiO₂) nanoparticles were prepared through the condensation reaction of polyvinyl alcohol and boric acid in the presence of TiO₂ nanoparticles. The solid-phase photocatalytic degradation of the polymer composites under UV light irradiation was investigated and compared with that of the pure PVB with the aid of weight loss measurements. The introduction of the photocatalyst nanoparticles in PVB enhanced the solid-phase photocatalytic degradation of the polymer matrix under UV light irradiation. The structural and morphological properties of PVB/TiO₂ composites were analyzed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and UV-Vis spectroscopy, respectively. FTIR analysis revealed that PVB synthesis was successfully carried out in the presence of the photocatalyst nanoparticles. According to the morphological analyses, TiO₂ nanoparticles were well dispersed in the PVB matrix. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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11 pages, 4156 KiB

Open AccessArticle

The Synergistic Effect of Pyridinic Nitrogen and Graphitic Nitrogen of Nitrogen-Doped Graphene Quantum Dots for Enhanced TiO₂ Nanocomposites’ Photocatalytic Performance

by Fei Li, Ming Li, Yi Luo, Ming Li, Xinyu Li, Jiye Zhang and Liang Wang

Catalysts 2018, 8(10), 438; https://doi.org/10.3390/catal8100438 - 4 Oct 2018

Cited by 16 | Viewed by 4731

Abstract

In this study, nitrogen-doped graphene quantum dots (N-GQDs) and a TiO₂ nanocomposite were synthesized using a simple hydrothermal route. Ammonia water was used as a nitrogen source to prepare the N-GQDs. When optically characterized by UV-vis, N-GQDs reveal stronger absorption peaks in [...] Read more.

In this study, nitrogen-doped graphene quantum dots (N-GQDs) and a TiO₂ nanocomposite were synthesized using a simple hydrothermal route. Ammonia water was used as a nitrogen source to prepare the N-GQDs. When optically characterized by UV-vis, N-GQDs reveal stronger absorption peaks in the range of ultraviolet (UV) light than graphene quantum dots (GQDs). In comparison with GQDs/TiO₂ and pure TiO₂, the N-GQDs/TiO₂ have significantly improved photocatalytic performance. In particular, it was found that, when the added amount of ammonia water was 50 mL, the content of pyridinic N and graphitic N were as high as 22.47% and 31.44%, respectively. Most important, the photocatalytic activity of N-GQDs/TiO₂-50 was about 95% after 12 min. The results illustrated that pyridinic N and graphitic N play a significant role in photocatalytic performance. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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10 pages, 1662 KiB

Open AccessCommunication

Improving Interfacial Charge-Transfer Transitions in Nb-Doped TiO₂ Electrodes with 7,7,8,8-Tetracyanoquinodimethane

by Reo Eguchi, Yuya Takekuma, Tsuyoshi Ochiai and Morio Nagata

Catalysts 2018, 8(9), 367; https://doi.org/10.3390/catal8090367 - 30 Aug 2018

Cited by 3 | Viewed by 3775

Abstract

Interfacial charge-transfer (ICT) transitions involved in charge-separation mechanisms are expected to enable efficient photovoltaic conversions through one-step charge-separation processes. With this in mind, the charge-transfer complex fabricated from TiO₂ nanoparticles and 7,7,8,8-tetracyanoquinodimethane (TCNQ) has been applied to dye-sensitized solar cells. However, rapid [...] Read more.

Interfacial charge-transfer (ICT) transitions involved in charge-separation mechanisms are expected to enable efficient photovoltaic conversions through one-step charge-separation processes. With this in mind, the charge-transfer complex fabricated from TiO₂ nanoparticles and 7,7,8,8-tetracyanoquinodimethane (TCNQ) has been applied to dye-sensitized solar cells. However, rapid carrier recombination from the conduction band of TiO₂ to the highest occupied molecular orbital (HOMO) of TCNQ remains a major issue for this complex. In this study, to inhibit surface-complex recombinations, we prepared Nb-doped TiO₂ nanoparticles with different atomic ratios for enhanced electron transport. To investigate the effects of doping on electron injection through ICT transitions, these materials were examined as photoelectrodes. When TiO₂ was doped with 1.5 mol % Nb, the Fermi level of the TiO₂ electrode shifted toward the conduction band minimum, which improved electron back-contact toward the HOMO of TCNQ. The enhancement in electron transport led to increases in both short circuit current and open circuit voltage, resulting in a slight (1.1% to 1.3%) improvement in photovoltaic conversion efficiency compared to undoped TiO₂. Such control of electron transport within the photoelectrode is attributed to improvements in electron injection through ICT transitions. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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10 pages, 2536 KiB

Open AccessArticle

Photocatalytic Antibacterial Effectiveness of Cu-Doped TiO₂ Thin Film Prepared via the Peroxo Sol-Gel Method

by Benjawan Moongraksathum, Jun-Ya Shang and Yu-Wen Chen

Catalysts 2018, 8(9), 352; https://doi.org/10.3390/catal8090352 - 27 Aug 2018

Cited by 55 | Viewed by 6524

Abstract

Cu-doped titanium dioxide thin films (Cu/TiO₂) were prepared on glass substrate via peroxo sol-gel method and dip-coating process with no subsequent calcination process for the degradation of organic dye and use as an antibacterial agent. The as-prepared materials were characterised using [...] Read more.

Cu-doped titanium dioxide thin films (Cu/TiO₂) were prepared on glass substrate via peroxo sol-gel method and dip-coating process with no subsequent calcination process for the degradation of organic dye and use as an antibacterial agent. The as-prepared materials were characterised using transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). For photocatalytic degradation of methylene blue in water, the samples were subjected to Ultraviolet C (UVC) and visible light irradiation. Degraded methylene blue concentration was measured using UV-Vis spectrophotometer. The antibacterial activities of the samples were tested against the gram-negative bacteria Escherichia coli (ATCC25922). Copper species were present in the form of CuO on the surface of modified TiO₂ particles, which was confirmed using TEM and XPS. The optimal observed Cu/TiO₂ weight ratio of 0.5 represents the highest photocatalytic activities under both UVC and visible light irradiation. Moreover, the same composition remarkably exhibited high antibacterial effectiveness against E. coli after illumination with ultraviolet A. The presence of CuO on TiO₂ significantly enhanced photocatalytic activities. Therefore, active Cu-doped TiO₂ can be used as a multipurpose coating material. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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14 pages, 3602 KiB

Open AccessArticle

Modification to L-H Kinetics Model and Its Application in the Investigation on Photodegradation of Gaseous Benzene by Nitrogen-Doped TiO₂

by Peng Sun, Jun Zhang, Wenxiu Liu, Qi Wang and Wenbin Cao

Catalysts 2018, 8(8), 326; https://doi.org/10.3390/catal8080326 - 9 Aug 2018

Cited by 34 | Viewed by 5712

Abstract

In this paper, the Langmuir-Hinshelwood (L-H) model has been used to investigate the kinetics of photodegradation of gaseous benzene by nitrogen-doped TiO₂ (N-TiO₂) at 25 °C under visible light irradiation. Experimental results show that the photoreaction coefficient k_pm increased [...] Read more.

In this paper, the Langmuir-Hinshelwood (L-H) model has been used to investigate the kinetics of photodegradation of gaseous benzene by nitrogen-doped TiO₂ (N-TiO₂) at 25 °C under visible light irradiation. Experimental results show that the photoreaction coefficient k_pm increased from 3.992 × 10⁻⁶ mol·kg⁻¹·s⁻¹ to 11.55 × 10⁻⁶ mol·kg⁻¹·s⁻¹ along with increasing illumination intensity. However, the adsorption equilibrium constant K_L decreased from 1139 to 597 m³·mol⁻¹ when the illumination intensity increased from 36.7 × 10⁴ lx to 75.1 × 10⁴ lx, whereas it was 2761 m³·mol⁻¹ in the absence of light. This is contrary to the fact that K_L should be a constant if the temperature was fixed. This phenomenon can be attributed to the breaking of the adsorption-desorption equilibrium by photocatalytically decomposition. To compensate for the disequilibrium of the adsorption-desorption process, photoreaction coefficient k_pm was introduced to the expression of K_L and the compensation form was denoted as K_m. K_L is an indicator of the adsorption capacity of TiO₂ while K_m is only an indicator of the coverage ratio of TiO₂ surface. The modified L-H model has been experimentally verified so it is expected to be used to predict the kinetics of the photocatalytic degradation of gaseous benzene. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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Review

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32 pages, 9254 KiB

Open AccessFeature PaperReview

Insights into the TiO₂-Based Photocatalytic Systems and Their Mechanisms

by Mohan Sakar, Ravikumar Mithun Prakash and Trong-On Do

Catalysts 2019, 9(8), 680; https://doi.org/10.3390/catal9080680 - 9 Aug 2019

Cited by 113 | Viewed by 17343

Abstract

Photocatalysis is a multifunctional phenomenon that can be employed for energy applications such as H₂ production, CO₂ reduction into fuels, and environmental applications such as pollutant degradations, antibacterial disinfection, etc. In this direction, it is not an exaggerated fact that TiO [...] Read more.

Photocatalysis is a multifunctional phenomenon that can be employed for energy applications such as H₂ production, CO₂ reduction into fuels, and environmental applications such as pollutant degradations, antibacterial disinfection, etc. In this direction, it is not an exaggerated fact that TiO₂ is blooming in the field of photocatalysis, which is largely explored for various photocatalytic applications. The deeper understanding of TiO₂ photocatalysis has led to the design of new photocatalytic materials with multiple functionalities. Accordingly, this paper exclusively reviews the recent developments in the modification of TiO₂ photocatalyst towards the understanding of its photocatalytic mechanisms. These modifications generally involve the physical and chemical changes in TiO₂ such as anisotropic structuring and integration with other metal oxides, plasmonic materials, carbon-based materials, etc. Such modifications essentially lead to the changes in the energy structure of TiO₂ that largely boosts up the photocatalytic process via enhancing the band structure alignments, visible light absorption, carrier separation, and transportation in the system. For instance, the ability to align the band structure in TiO₂ makes it suitable for multiple photocatalytic processes such as degradation of various pollutants, H₂ production, CO₂ conversion, etc. For these reasons, TiO₂ can be realized as a prototypical photocatalyst, which paves ways to develop new photocatalytic materials in the field. In this context, this review paper sheds light into the emerging trends in TiO₂ in terms of its modifications towards multifunctional photocatalytic applications. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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22 pages, 7541 KiB

Open AccessReview

Titanium-Dioxide-Based Visible-Light-Sensitive Photocatalysis: Mechanistic Insight and Applications

by Shinya Higashimoto

Catalysts 2019, 9(2), 201; https://doi.org/10.3390/catal9020201 - 22 Feb 2019

Cited by 81 | Viewed by 11669

Abstract

Titanium dioxide (TiO₂) is one of the most practical and prevalent photo-functional materials. Many researchers have endeavored to design several types of visible-light-responsive photocatalysts. In particular, TiO₂-based photocatalysts operating under visible light should be urgently designed and developed, in [...] Read more.

Titanium dioxide (TiO₂) is one of the most practical and prevalent photo-functional materials. Many researchers have endeavored to design several types of visible-light-responsive photocatalysts. In particular, TiO₂-based photocatalysts operating under visible light should be urgently designed and developed, in order to take advantage of the unlimited solar light available. Herein, we review recent advances of TiO₂-based visible-light-sensitive photocatalysts, classified by the origins of charge separation photo-induced in (1) bulk impurity (N-doping), (2) hetero-junction of metal (Au NPs), and (3) interfacial surface complexes (ISC) and their related photocatalysts. These photocatalysts have demonstrated useful applications, such as photocatalytic mineralization of toxic agents in the polluted atmosphere and water, photocatalytic organic synthesis, and artificial photosynthesis. We wish to provide comprehension and enlightenment of modification strategies and mechanistic insight, and to inspire future work. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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32 pages, 8851 KiB

Open AccessEditor’s ChoiceReview

Titanium Dioxide: From Engineering to Applications

by Xiaolan Kang, Sihang Liu, Zideng Dai, Yunping He, Xuezhi Song and Zhenquan Tan

Catalysts 2019, 9(2), 191; https://doi.org/10.3390/catal9020191 - 19 Feb 2019

Cited by 366 | Viewed by 26126

Abstract

Titanium dioxide (TiO₂) nanomaterials have garnered extensive scientific interest since 1972 and have been widely used in many areas, such as sustainable energy generation and the removal of environmental pollutants. Although TiO₂ possesses the desired performance in utilizing ultraviolet light, [...] Read more.

Titanium dioxide (TiO₂) nanomaterials have garnered extensive scientific interest since 1972 and have been widely used in many areas, such as sustainable energy generation and the removal of environmental pollutants. Although TiO₂ possesses the desired performance in utilizing ultraviolet light, its overall solar activity is still very limited because of a wide bandgap (3.0–3.2 eV) that cannot make use of visible light or light of longer wavelength. This phenomenon is a deficiency for TiO₂ with respect to its potential application in visible light photocatalysis and photoelectrochemical devices, as well as photovoltaics and sensors. The high overpotential, sluggish migration, and rapid recombination of photogenerated electron/hole pairs are crucial factors that restrict further application of TiO₂. Recently, a broad range of research efforts has been devoted to enhancing the optical and electrical properties of TiO₂, resulting in improved photocatalytic activity. This review mainly outlines state-of-the-art modification strategies in optimizing the photocatalytic performance of TiO₂, including the introduction of intrinsic defects and foreign species into the TiO₂ lattice, morphology and crystal facet control, and the development of unique mesocrystal structures. The band structures, electronic properties, and chemical features of the modified TiO₂ nanomaterials are clarified in detail along with details regarding their photocatalytic performance and various applications. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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27 pages, 7168 KiB

Open AccessEditor’s ChoiceReview

Titanium Dioxide (TiO₂) Mesocrystals: Synthesis, Growth Mechanisms and Photocatalytic Properties

by Boxue Zhang, Shengxin Cao, Meiqi Du, Xiaozhou Ye, Yun Wang and Jianfeng Ye

Catalysts 2019, 9(1), 91; https://doi.org/10.3390/catal9010091 - 16 Jan 2019

Cited by 59 | Viewed by 9146

Abstract

Hierarchical TiO₂ superstructures with desired architectures and intriguing physico-chemical properties are considered to be one of the most promising candidates for solving the serious issues related to global energy exhaustion as well as environmental deterioration via the well-known photocatalytic process. In particular, [...] Read more.

Hierarchical TiO₂ superstructures with desired architectures and intriguing physico-chemical properties are considered to be one of the most promising candidates for solving the serious issues related to global energy exhaustion as well as environmental deterioration via the well-known photocatalytic process. In particular, TiO₂ mesocrystals, which are built from TiO₂ nanocrystal building blocks in the same crystallographical orientation, have attracted intensive research interest in the area of photocatalysis owing to their distinctive structural properties such as high crystallinity, high specific surface area, and single-crystal-like nature. The deeper understanding of TiO₂ mesocrystals-based photocatalysis is beneficial for developing new types of photocatalytic materials with multiple functionalities. In this paper, a comprehensive review of the recent advances toward fabricating and modifying TiO₂ mesocrystals is provided, with special focus on the underlying mesocrystallization mechanism and controlling rules. The potential applications of as-synthesized TiO₂ mesocrystals in photocatalysis are then discussed to shed light on the structure–performance relationships, thus guiding the development of highly efficient TiO₂ mesocrystal-based photocatalysts for certain applications. Finally, the prospects of future research on TiO₂ mesocrystals in photocatalysis are briefly highlighted. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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25 pages, 9773 KiB

Open AccessReview

Compositing Two-Dimensional Materials with TiO₂ for Photocatalysis

by Yu Ren, Yuze Dong, Yaqing Feng and Jialiang Xu

Catalysts 2018, 8(12), 590; https://doi.org/10.3390/catal8120590 - 28 Nov 2018

Cited by 41 | Viewed by 9447

Abstract

Energy shortage and environmental pollution problems boost in recent years. Photocatalytic technology is one of the most effective ways to produce clean energy—hydrogen and degrade pollutants under moderate conditions and thus attracts considerable attentions. TiO₂ is considered one of the best photocatalysts [...] Read more.

Energy shortage and environmental pollution problems boost in recent years. Photocatalytic technology is one of the most effective ways to produce clean energy—hydrogen and degrade pollutants under moderate conditions and thus attracts considerable attentions. TiO₂ is considered one of the best photocatalysts because of its well-behaved photo-corrosion resistance and catalytic activity. However, the traditional TiO₂ photocatalyst suffers from limitations of ineffective use of sunlight and rapid carrier recombination rate, which severely suppress its applications in photocatalysis. Surface modification and hybridization of TiO₂ has been developed as an effective method to improve its photocatalysis activity. Due to superior physical and chemical properties such as high surface area, suitable bandgap, structural stability and high charge mobility, two-dimensional (2D) material is an ideal modifier composited with TiO₂ to achieve enhanced photocatalysis process. In this review, we summarized the preparation methods of 2D material/TiO₂ hybrid and drilled down into the role of 2D materials in photocatalysis activities. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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99 pages, 25940 KiB

Open AccessFeature PaperReview

Heterogeneous Photocatalysis and Prospects of TiO₂-Based Photocatalytic DeNOxing the Atmospheric Environment

by Nick Serpone

Catalysts 2018, 8(11), 553; https://doi.org/10.3390/catal8110553 - 16 Nov 2018

Cited by 62 | Viewed by 9653

Abstract

This article reviews the efforts of the last two decades to deNOxify the atmospheric environment with TiO₂-based photocatalytic materials supported on various cementitious-like substrates. Prior to undertaking this important aspect of applied photocatalysis with metal-oxide emiconductor photocatalysts, however, it is pertinent [...] Read more.

This article reviews the efforts of the last two decades to deNOxify the atmospheric environment with TiO₂-based photocatalytic materials supported on various cementitious-like substrates. Prior to undertaking this important aspect of applied photocatalysis with metal-oxide emiconductor photocatalysts, however, it is pertinent to describe and understand the fundamentals of Heterogeneous Photocatalysis. The many attempts done in a laboratory setting to degrade (deNOxify) the major components that make up the NO_x, namely nitric oxide (NO) and nitrogen dioxide (NO₂), but most importantly the efforts expended in deNOxifying the real environment upon depositing titania-based coatings on various model and authentic infrastructures, such as urban roads, highway noise barriers, tunnels, and building external walls among others, are examined. Both laboratory and outdoor experimentations have been performed toward NO_x being oxidized to form nitrates (NO₃⁻) that remain adsorbed on the TiO₂-based photocatalytic surfaces (except in tunnels—indoor walls) but get subsequently dislodged by rain or by periodic washings of the infrastructures. However, no serious considerations have been given to the possible conversion of NO_x via photocatalytic reduction back to N₂ and O₂ gases that would restore the atmospheric environment, as the adsorbed nitrates block the surface-active sites of the photocatalyst and when washed-off ultimately cause unduly damages to the environment. Full article

(This article belongs to the Special Issue Emerging Trends in TiO₂ Photocatalysis and Applications)

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