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2014, Materials
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2012, International Journal of Photoenergy
2013, Solid State Sciences
Various human activities like mining and extraction of mineral oils have been used for the modernization of society and well-beings. However, the by-products such as petrochemical wastes generated from such industries are carcinogenic and toxic, which had increased environmental pollution and risks to human health several folds. Various methods such as physical, chemical and biological methods have been used to degrade these pollutants from wastewater. Advance oxidation processes (AOPs) are evolving techniques for efficient sequestration of chemically stable and less biodegradable organic pollutants. In the present review, photocatalytic degradation of petrochemical wastes containing monoaromatic and poly-aromatic hydrocarbons has been studied using various heterogeneous photocatalysts (such as TiO 2 , ZnO and CdS. The present article seeks to offer a scientific and technical overview of the current trend in the use of the photocatalyst for remediation and degradation of petrochemical waste depending upon the recent advances in photodegradation of petrochemical research using bibliometric analysis. We further outlined the effect of various heterogeneous catalysts and their ecotoxicity, various degradation pathways of petrochemical wastes, the key regulatory parameters and the reactors used. A critical analysis of the available literature revealed that TiO 2 is widely reported in the degradation processes along with other semiconductors/nanomaterials in visible and UV light irradiation. Further, various degradation studies have been carried out at laboratory scale in the presence of UV light. However, further elaborative research is needed for successful application of the laboratory scale techniques to pilot-scale operation and to develop environmental friendly catalysts which support the sustainable treatment technology with the Bzero concept^ of industrial wastewater. Nevertheless, there is a need to develop more effective methods which consume less energy and are more efficient in pilot scale for the demineral-ization of pollutant.
2014, Journal of the Air & Waste Management Association
The sol-gel process is a wet-chemical technique (chemical solution deposition), which has been widely used in the fields of materials science, ceramic engineering, and especially in the preparation of photocatalysts. Volatile organic compounds (VOCs) are prevalent components of indoor air pollution. Among the approaches to remove VOCs from indoor air, photocatalytic oxidation (PCO) is regarded as a promising method. This paper is a review of the status of research on the sol-gel method for photocatalyst preparation and for the PCO purification of VOCs. The review and discussion will focus on the preparation and coating of various photocatalysts, operational parameters, and will provide an overview of general PCO models described in the literature.
2019, Cu.N-codoped TiO2 prepared by the sol-gel method for phenanthrene removal under visible light irradiation
Cu/N-codoped TiO 2 nanoparticles were prepared by the modified sol-gel method, to study its efficiency for the removing of polyaromatic hydrocarbon (phenanthrene) from an aqueous solution. Urea and copper sulfate pentahydrate were used as sources of doping element for Cu/N-codoped TiO 2 , respectively. The characterizations of the nanoparticles were done by X-ray diffrac-tion (XRD), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectra. XRD revealed that all the nano-particles were indexed to the anatase phase structure, with crystallite size range from 11 to 30 nm, which decreased with the doping of copper and nitrogen. The photocatalytic activities of Cu/N-codoped TiO 2 showed the highest activities than other TiO 2 nanoparticles (TiO 2 and N-doped TiO 2). The photodegradation efficiency of Cu/N-codoped TiO 2 on phenanthrene under visible light irradiation was slightly higher (96%) comparing to UV light irradiation (94%). Cu/N-codoped TiO 2 was found to be very efficient and economical for phenanthrene removal, because the smallest amount of Cu/N-codoped TiO 2 exhibited the best removal efficiency on phenanthrene.
2009
2013, Materials Chemistry and Physics
2019, Photocatalytic Removal of Methylbenzene Vapors by MnO2/Al2O3/Fe2O3 Nano composite
Methyl benzene, which has carcinogenic effects, is a volatile organic compound that is widely used in various industries. Nano composites of Mno2/Al203/Fe203, which is a new photocatalyst, have not been applied to remove contaminants from air streams. Therefore, the aim of the present study was to investigate the photocatalytic removal of ethyl benzene by using this nano composite activated by visible light. Morphological characteristics of the synthesized Nano composite in a sol-gel method are determined through XRD, FTIR, and SEM. Through the photocatalyst process and by the use of visible light radiation, the synthesized Nano composite is used to degrade ethyl benzene in the gas phase. In order to estimate the main effects and interaction ones and to optimize the experiment numbers, the response surface method was used. Operational parameters investigated in the study are the initial concentration of contaminants, relative humidity, and the residence time, which were considered in three levels; further, the experiments were designed by Design Expert version 9 software. The results show the Nano composite particle sizes were less than 82 nanometers. The findings also indicate that relative humidity and residence time were effective parameters in removal efficiency of ethyl benzene. This Nano composite, at the optimal conditions, was capable of removing 98.72% of the pollutants, with an initial content of 300 ppm. MnO2/Al2O3/Fe2O3 Nano composite is a suitable catalyst to remove ethyl benzene from air streams. Among the features of the Nano composite are reaction at room temperature and lower production dangerous byproducts, which are the main advantages of this Nano composite as compared with other nano composites.
2013, Powder Technology
Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO2) semiconductor materials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applications. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 structure, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochemical and photoelectrochemical methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purification, are illustrated. Comprehensive studies on the photocatalytic degradation of contaminants of emerging concern, including endocrine disrupting compounds, pharmaceuticals, pesticides, cyanotoxins and volatile organic compounds, with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bacterial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.
2014, Materials
Cojocariu
Volatile organic compounds (VOCs) are ubiquitous in indoor environments. Inhalation of VOCs can cause irritation, difficulty breathing, and nausea, and damage the central nervous system as well as other organs. Formaldehyde is a particularly important VOC as it is even a carcinogen. Removal of VOCs is thus critical to control indoor air quality (IAQ). Photocatalytic oxidation has demonstrated feasibility to remove toxic VOCs and formaldehyde from indoor environments. The technique is highly-chemical stable, inexpensive, non-toxic, and capable of removing a wide variety of organics under light irradiation. In this paper, we review and summarize the traditional air cleaning methods and current photocatalytic oxidation approaches in both of VOCs and formaldehyde degradation in indoor environments. Influencing factors such as temperature, relative humidity, deactivation and reactivations of the photocatalyst are discussed. Aspects of the application of the photocatalytic technique to improve the IAQ are suggested.
Though there are many advantages for the TiO2 compared to other semiconductor photocatalysts, its band gap of 3.2 eV restrains application to the UV-region of the electromagnetic spectrum ( ≤ 387.5 nm). As a result, development of visible-light active titanium dioxide is one of the key challenges in the field of semiconductor photocatalysis. In this review, advances in the strategies for the visible light activation, origin of visible-light activity, and electronic structure of various visible-light active TiO2 photocatalysts are discussed in detail. It has also been shown that if appropriate models are used, the theoretical insights can successfully be employed to develop novel catalysts to enhance the photocatalytic performance in the visible region. Recent developments in theory and experiments in visible-light induced water splitting, degradation of environmental pollutants, water and air purification and antibacterial applications are also reviewed. Various strategies to identify appropriate dopants for improved visible-light absorption and electron–hole separation to enhance the photocatalytic activity are discussed in detail, and a number of recommendations are also presented.
ZnO nanowires (or nanorods) have been widely studied due to their unique material properties and remarkable performance in electronics, optics, and photonics. Recently, photocatalytic applications of ZnO nanowires are of increased interest in environmental protection applications. This paper presents a review of the current research of ZnO nanowires (or nanorods) with special focus on photocatalysis. We have reviewed the semiconducting photocatalysts and discussed a variety of synthesis methods of ZnO nanowires and their corresponding effectiveness in photocatalysis. We have also presented the characterization of ZnO nanowires from the literature and from our own measurements. Finally, a wide range of uses of ZnO nanowires in various applications is highlighted in this paper.
TiO 2 is an effective and well-known photocatalyst for water and air purification, but its practical applications in visible light-assisted chemical reactions are hindered mainly by its poor visible light absorption capacity. Nitrogen-doped TiO 2 (N-doped TiO 2) has attracted considerable attention as a photocatalyst, and rapid progress has been made in enhancing the photocatalytic efficiency of TiO 2 under visible light irradiation. N-doped TiO 2 exhibits broad absorption in the visible region, which can allow the utilization of a large part of the solar spectrum. This might be useful for environmental and energy applications, such as the photocatalytic degradation of organic pollutants, solar cells, sensors, and water splitting reactions. This review focuses on the major developments in the synthesis of N-doped TiO 2 and its possible applications in the photocatalytic degradation of organic pollutants and environmental remediation under visible light irradiation.
2011, Chemosphere
2014, Applied Surface Science
It is now extensively established that the ideal way to achieve the development in heterogeneous ca-talysis is to utilize semiconducting titanium dioxide (TiO2) based particles with high surface area as well as mesoporous structure. This can efficiently accommodate substrates on its surface to interact with each other. Most of the reduction-oxidation type organic transformations, degradation of hazardous organic moieties are feasible at moderate reaction conditions with the help of TiO2 nanoparticles due to their ability to form composites with enhanced performance, better metal support interactions, chemical stability, selectivity and presence of reactive acid-base sites on its surface. This review article provides a balanced and comprehensive analysis of some innovative and ambitious strategies for modification of TiO2 host material for heterogeneous catalysis: a) making its composites with other materials; and b) doping by metal or non-metal.
2016
Heterogeneous photocatalysis is a promising technology especially for environmental remediation. Despite more than a decade of worldwide research in developing photocatalytic efficiency improving techniques, many questions regarding the large scale application of photocatalytic reactors still remain unanswered. Recently, improving the photocatalytic efficiency has gained scientific attention because it might lead to more economical and robust photocatalytic operation for environmental remediation. In this review, fundamental and comprehensive assessments of the photocatalytic concepts and their applications for environmental remediation are reviewed. The existing challenges and strategies to improve the photocatalytic efficiency are discussed. Further, recent developments and future research prospects on photocatalytic systems for environmental applications are also addressed.
2015, Building and Environment
Mesoporous titania (mp-TiO2) has drawn tremendous attention for a diverse set of applications due to its high surface area, interfacial structure, and tunable combination of pore size, pore orientation, wall thickness, and pore connectivity. Its pore structure facilitates rapid diffusion of reactants and charge carriers to the photocatalytically active interface of TiO2. However, because the large band gap of TiO2 limits its ability to utilize visible light, non-metal doping has been extensively studied to tune the energy levels of TiO2. While first-principles calculations support the efficacy of this approach, it is challenging to efficiently introduce active non-metal dopants into the lattice of TiO2. This review surveys recent advances in the preparation of mp-TiO2 and their doping with non-metal atoms. Different doping strategies and dopant sources are discussed. Further, co-doping with combinations of non-metal dopants are discussed as strategies to reduce the band gap, improve photogenerated charge separation, and enhance visible light absorption. The improvements resulting from each doping strategy are discussed in light of potential changes in mesoporous architecture, dopant composition and chemical state, extent of band gap reduction, and improvement in photocatalytic activities. Finally, potential applications of non-metal-doped mp-TiO2 are explored in water splitting, CO2 reduction, and environmental remediation with visible light.
It is now extensively established that the ideal way to achieve the development in heterogeneous catalysis is to utilize semiconducting titanium dioxide (TiO2) based particles with high surface area as well as mesoporous structure. This can efficiently accommodate substrates on its surface to interact with each other. Most of the reduction-oxidation type organic transformations, degradation of hazardous organic moieties are feasible at moderate reaction conditions with the help of TiO2 nanoparticles due to their ability to form composites with enhanced performance, better metal support interactions, chemical stability, selectivity and presence of reactive acid-base sites on its surface. This review article provides a balanced and comprehensive analysis of some innovative and ambitious strategies for modification of TiO2 host material for heterogeneous catalysis: a) making its composites with other materials; and b) doping by metal or non-metal.
Herein, we report the synthesis of quartz supported TiO 2 photocatalysts codoped with carbon and silver through the hydrolysis of titanium tetrachloride followed by calcination at 500 ∘ C. The prepared samples were characterized by UV-Vis diffuse reflectance spectroscopy, high resolution scanning electron microscopy (HRSEM), Raman spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Codoping of TiO 2 with Ag and carbon resulted in an increase in the surface area of the photocatalyst and altered the ratio of the anatase to rutile phase. The absorption edge of all the doped TiO 2 photocatalysts redshifted and the band gap was reduced. The lowest band gap of 1.95 eV was achieved by doping with 0.5% Ag. Doping TiO 2 using carbon as the only dopant resulted in a quartz supported photocatalyst that showed greater photocatalytic activity towards methyl orange than undoped TiO 2 and also all codoped TiO 2 photocatalysts under visible light irradiation.
In the present study, we have adopted a simple one-pot alkaline hydrothermal route to synthesize Bi-doped TiO 2 NT/graphene composites by using different wt% of Bi with an aim to achieve the excellent photocatalytic activity under visible light source. The nature of GO is changed to deoxygenated graphene with simultaneous embedding of Bi into TiO 2 nanotube (TNT), during hydrothermal process. XRD and FTIR analysis confirm the successful conversion of GO to deoxygenated graphene. EPR analysis reveals the coexistence of Ti 3+ ion with oxygen vacancy, which is created by the Bi doping. The photocatalytic activity of the prepared samples is measured by the degradation of aqueous suspensions of methylene blue (MB) and Dinoseb (phenolic herbicide), under visible-light irradiation. The prepared TiO 2 NT/graphene composite with 2-wt% bismuth (2-BTNTG) has shown the improved photocatalytic activity as compared to their counterparts. The improved photocatalytic activity is associated to the synergistic effect of graphene and Bi-TNT, which facilitate the interfacial charge transfer and enhances the efficiency of light harvesting in the visible region. Moreover, the underlying mechanism involving photocatalytic degradation of organic pollutants over 2-BTNTG is explored by using trapping experiments, suggesting that the. OH radicals solely contributed to degradation.
Atrazine is one of the most extensively used herbicides. Being non-biodegradable in nature, it has a long half-life in water and hence it is prone to contaminate the water bodies and even seeps into the ground to pollute underground water. In this study, we developed a photocatalytic method for the degradation of Atrazine in water samples. Highly ordered mesoporous Ag-WO 3 /SBA-15 composites were tested as photocatalysts for the degradation of atrazine in water. It was found that 40% WO 3 loading rendered an optimum surface area and material content in the SBA-15 template and hence favored the enhanced photocatalytic degradation of atrazine in water. The further addition of Ag onto the WO 3 /SBA-15 composite not only made this catalyst very effective in the most sought visible region due to solar energy harvesting, but also significantly reduced the electron hole recombination as evidenced by photolumi-nescence studies to enhance the degradation efficiency. As a result, the Ag-WO 3 /SBA-15 composite the photo-catalytic degradation of atrazine in water under visible radiation was significantly enhanced.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights The photocatalytic activity of V-modified N/Si-co-doped TiO 2 was characterized. The photocatalyst exhibited high dispersibility in aqueous solution. The isoelectric point was lowered by modifying N/Si–TiO 2 with vanadium. The photocatalyst could effectively decompose DMSO in water under visible light. a b s t r a c t We report the characterization of vanadium-modified N/Si co-doped TiO 2 (VNSiT) in an aqueous solution and its capacity for the photocatalytic decomposition of dimethyl sulfoxide (DMSO) and methylene blue (MB) under visible light irradiation. The two synthesized VNSiTs were V(0.005)–NSiT and V(0.02)–NSiT, which contained different amounts of V 2 O 5 mounted on N-doped Si(0.2)–TiO 2 (NSiT) by annealing at 600 °C. The VNSiTs exhibited absorbance in the range of 420–520 nm. The isoelectric points of both were three, which is much lower than that of bare TiO 2 due to the presence of the negatively charged vanadium species (e.g., vanadate) in the VNSiTs. This resulted in particles with a small average hydrodynamic diameter and high dispersibility formed at pH 7–10 in an aqueous solution. The decomposition rate of DMSO, which is an OH radical scavenger, in the presence of V(0.005)–NSiT and V(0.02)–NSiT under visible light irradiation for 10 h was 40% and 29%, respectively. It was found that an excess of vanadium species caused a decrease in the decomposition efficiency of DMSO. In addition, the VNSiTs strongly adsorbed MB, a basic dye, under dark conditions, but could not decompose it under visible light irradiation possibly because of the strong electrostatic attraction of the VNSiTs to the ionic MB species in water.
2014, ACS nano
Titanium dioxide (TiO2), as an excellent photocatalyst, has been intensively investigated and widely used in environmental purification. However, the wide band gap of TiO2 and rapid recombination of photogenerated charge carriers significantly limit its overall photocatalytic efficiency. Here, efficient visible-light-active photocatalysts were developed on the basis of TiO2 modified with two ubiquitous nanoclusters. In this photocatalytic system, amorphous Ti(IV) oxide nanoclusters were demonstrated to act as hole-trapping centers on the surface of TiO2 to efficiently oxidize organic contaminants, while amorphous Fe(III) or Cu(II) oxide nanoclusters mediate the reduction of oxygen molecules. Ti(IV) and Fe(III) nanoclusters-modified TiO2 exhibited the highest quantum efficiency (QE = 92.2%) and reaction rate (0.69 μmol/h) for 2-propanol decomposition among previously reported photocatalysts, even under visible-light irradiation (420-530 nm). The desirable properties of efficient phot...
2006, Industrial & Engineering Chemistry Research
2013, Chemical Engineering Journal
Different types of TiO2 –SiO2 composites in the form of powder or films have been reported as efficient photocatalysts for decomposition of organic compounds in liquid and gas phase. Herein, we report for the first time on the formation of efficient TiO2 –SiO2 films made from acidic organic-free colloidal solution of TiO 2 anatase nanoparticles (AS) and mesoporous SiO2 (SBA-15) with 100% loading (TiO2 : SiO2 molar ratio 1:1) under simple and low cost procedure. AS was prepared from metatitanic acid precursor using a novel, environmentally friendly approach of TiO2 nanoparticles precipitation with NaOH and peptiza-tion with HCl. These AS/SBA-15 films, immobilized by brush deposition on glass carriers, showed total decomposition of toluene and 91% decomposition of formaldehyde as model VOCs in gas phase, at room temperature under UVA irradiation in lab-made batch photoreactor. The trend of photocatalytic efficiency for decomposition of formaldehyde was AS/SBA-15 > P25 > PC500 > AS. The adsorption capability of the AS/SBA-15 was higher in comparison to its pure TiO2 analogues (AS, P25, PC500) in case of toluene. Turnover frequency (TOF) of the AS/SBA-15 was approximately six times higher in comparison to its pure TiO2 analogue AS for toluene and formaldehyde. The potential of AS/SBA-15 for the use in air cleaning devices is finally discussed.
A series of Y and V co-doped ZnO (YVZ) nanoparticles have been synthesized by surfactant assisted sol gel method with an aim to enhance the photocatalytic activity under visible light for degradation of organic pollutants. The prepared samples were characterized by standard analytical techniques such as XRD, XPS, SEM-EDX, TEM, UV–vis spectroscopy, FT-IR, BET, TGA and PL spectroscopy. The XRD analysis clarifies the coexistence of Y and V into ZnO as evidenced by the shift of plane towards the lower theta value. The photodegradation performances of the prepared samples were evaluated by studying the degradation of Rhodamine B (RhB), Methylene Blue (MB) and 4-nitrophenol (4-NP) under visible light irradiation. Among the series of synthesized YVZ nanoparticles, 3-YVZ (3%Y/1%V-ZnO) was found to be the most active photocatalyst for the degradation of organic pollutants under investigation. This remarkably improved photocatalytic activity of 3-YVZ could be attributed to the strong absorption of visible light and effective separation of photoinduced e −-h + pair. The mineralization of RhB was investigated by measuring the COD depletion as a function of time. In addition, the influence of operational parameters such as, catalyst dosage and initial reaction pH was optimized with most active 3-YVZ photocatalyst for degradation of RhB as a function of time. The quenching experiments were conducted to determine the main reactive species formed in the reaction mixture and accordingly a mechanism for enhanced photocatalytic activity has been proposed.
2013, International Journal of Photoenergy
Self-organized TiO2 nanotubes (TNTs) with average inner diameter of 109 nm, wall thickness of 15 nm, and tube length of 7-10 m were loaded with nickel oxide (NiO) nanoparticles via incipient wet impregnation method. The molar concentration of Ni(NO3)2·6H2O aqueous solution varied in a range of 0.5 M-2.5 M. The samples were characterized for crystalline phase, morphology, topography, chemical composition, Raman shift, and UV-Vis diffusion reflection properties. The finding shows that the loading of NiO did not influence the morphology, structure, and crystalline phase of TNTs but it exhibited significant effect on crystallite size and optical absorption properties. Further, the solar-energy-driven the photocatalytic activity of NiO/TNTs and pure TNTs was evaluated by degrading methylene blue (MB). The results confirm that photocatalytic efficiency of NiO/TNTs is higher than that of TNTs. © 2013 Lan Ching Sim et al. http://www.hindawi.com/journals/ijp/2013/659013/
• N-Cu co-doped TiO 2 @CNTs was prepared , characterized and coupled with UV and US irradiations. • Photocatalytic activity of TiO 2 was accelerated significantly after doping of N and Cu. • Catalyst was recyclable after six consecutive runs with an insignificant decrease in performance. • Under optimized conditions, the removal efficiencies of 100, 93 and 89% were obtained for SMXZ, COD and TOC, respectively. • Sono-photocatalysis process showed a good performance for treatment of real pharmaceutical wastewater. A B S T R A C T In this study, N-Cu co-doped TiO 2 was decorated on the single-walled carbon nano-tube (marked as N-Cu co-doped TiO 2 @CNTs) via two-step sol-gel/hydrothermal synthesis method for the first time as a novel photo-catalyst in coupling with ultrasound (US) waves. The catalyst properties were characterized via BET, Raman, FESEM, TEM, FTIR, XRD, EIS, PL, TGA, UV-Vis DRS, EDX and EDS dot mapping. These techniques confirmed the successful doping of both N and Cu elements on the CNTs impregnated with TiO 2 nanoparticles. The investigation of effective operational parameters demonstrated that the total removal of sulfamethoxazole (SMXZ) could be achieved under pH of 6.0, catalyst dosage of 0.8 g/L, light intensity of 200 W, US power of 200 W, and initial SMXZ concentration of 60 mg/L within 60 min. SMXZ degradation kinetics over sono-photocatalytic process were in a good agreement with pseudo-first-order model. Quenching experiments illustrated that HO • and O 2 •-active species were more effective species for SMXZ degradation. The synthesized sono-photocatalyst could be recycled after six consecutive cycles of SMXZ degradation with an insignificant decrease in perfor-https://doi. T mance. A tentative mechanism and pathway for SMXZ were formulated. Pharmaceutical wastewater was treated through the optimum degradation conditions which showed that the sono-photocatalytic degradation eliminated 93% of COD and 89% of TOC within 180 min.
2009, Journal of Photochemistry and Photobiology A-chemistry
AIA Tutorial
2011, Chinese Science Bulletin
Climate change and the consumption of non-renewable resources are considered as the greatest problems facing humankind. Because of this, photocatalysis research has been rapidly expanding. TiO2 nanoparticles have been extensively investigated for photocatalytic applications including the decomposition of organic compounds and production of H2 as a fuel using solar energy. This article reviews the structure and electronic properties of TiO2, compares TiO2 with other common semiconductors used for photocatalytic applications and clarifies the advantages of using TiO2 nanoparticles. TiO2 is considered close to an ideal semiconductor for photocatalysis but possesses certain limitations such as poor absorption of visible radiation and rapid recombination of photogenerated electron/hole pairs. In this review article, various methods used to enhance the photocatalytic characteristics of TiO2 including dye sensitization, doping, coupling and capping are discussed. Environmental and energy applications of TiO2, including photocatalytic treatment of wastewater, pesticide degradation and water splitting to produce hydrogen have been summarized.
2019, J. Phys. Chem. C 2019, 123, 34, 21083-21096
The thermal stability of anatase titanium dioxide (TiO2) is a prerequisite to fabricate photocatalyst coated indoor building materials for use in antimicrobial and self-cleaning applications under normal room light illumination. Metal doping of TiO2 is an appropriate way to control the anatase to rutile phase transition (ART) at high processing temperature. In this present work, ART of indium (In) doped TiO2 (In-TiO2) was investigated in detail in the range of 500 °C-900 °C. In-TiO2 (In mol % = 0 to 16) was synthesized via a modified sol-gel approach. These nanoparticles were further characterized by means of powder X-ray diffraction (XRD), Raman, photoluminescence (PL), transient photocurrent response, and X-ray photoelectron spectroscopy (XPS) techniques. XRD results showed that the anatase phase was maintained up to 64 % by 16-mol % of In doping at 800 °C of calcination temperature. XPS results revealed that the binding energies of Ti 4+ (Ti 2p1/2 and Ti 2p3/2) were red-shifted by In doping. The influence of In doping on the electronic structure and oxygen vacancy formation of anatase TiO2 was studied using density functional theory corrected for on-site Coulomb interactions (DFT+U). First principles results showed that the charge compensating oxygen vacancies form spontaneously at sites adjacent to the In dopant. DFT+U calculations revealed the formation of In-5s states in the band gap of the anatase host. The formation of In2O3 at the anatase surface was also examined using a slab model of the anatase (101) surface modified with a nanocluster of composition In4O6. The formation of a reducing oxygen vacancy also has a moderate energy cost and results in charge localisation at In ions of the supported nanocluster. PL and photocurrent measurements suggested that the charge carrier recombination process in TiO2 was reduced in the presence of In dopant. The photocatalytic activity of 2 % In-TiO2 calcined at 700 °C is more comparable with that of pure anatase.