A Novel Method for Preparing V-doped Titanium Dioxide Thin Film Photocatalysts with High Photocatalytic Activity Under Visible Light Irradiation

The liquid phase deposition (LPD) method was successfully used for preparing V-doped TiO₂ thin film photocatalysts. In this simple and easily-controlled process, V-doped anatase TiO₂ thin films were directly deposited on a soda lime glass substrate placed in an aqueous solution containing Ti- and V-fluoro complex ions, followed by annealing. The thin films were analyzed by XRD, XPS, UV-vis. V⁴⁺ ions were introduced into the lattice of TiO₂ through in-situ substituting Ti⁴⁺. The absorption edge of V-doped TiO₂ films shifted to visible light region. The highly efficient photocatalytic activity was verified by the decomposition of methylene blue under visible light irradiation.     

Photocatalytic degradation of trace gaseous acetone and acetaldehyde using TiO2 supported on fiberglass cloth

The feasibility of photocatalytic degradation of trace gaseous acetone and acetaldehyde using TiO₂ supported on fiberglass cloth was studied. The results show that gaseous acetone and acetaldehyde can be completely photocatalytically degraded into CO₂ and H₂O, after 35 min illumination with a 375 W medium pressure mercury lamp. The effects of parameters such as the flow of reactant gases and the concentrations of oxygen and water vapor in the feed stream on the photocatalytic degradation were studied. TiO₂ supported on fiberglass cloth was not easily detached. After 150 h illumination there was no significant loss of the photocatalytic activity of TiO₂. © 1998 Society of Chemical Industry     

Li–Y doped and codoped TiO2 thin films: Enhancement of photocatalytic activity under visible light irradiation

Sol−gel synthesis based on the self-assembling template method has been applied to synthesize Li–Y doped and co-doped TiO₂ not only to improve simultaneously the structural and electronic properties of TiO₂ nanomaterials but also to achieve Li–Y doping of titania with high photocatalytic reactivity. The characterization of the samples was performed by GXRD, GSDR, FT-IR, and Raman spectroscopy. According to the GXRD patterns, all the observed reflections can be indexed using the anatase form of TiO₂, Which is confirmed by ground state diffuse reflectance and micro-Raman spectra. The Li–Y doped titania materials immobilized as nanostructured thin films on glass substrates exhibit high photocatalytic efficiency for the degradation of toluidine and benzoic acid under visible light irradiation. The development of these visible light-activated nanocatalysts has the potential of providing environmentally benign routes for water treatment.     

One-pot synthesis of bifunctionalized TiO<Subscript>2</Subscript> mesoporous photocatalyst with visible light response

A series of Fe-doped SH/TiO₂ mesoporous photocatalysts have been firstly prepared by one-pot method using P123 as structure-directing agent. This bifunctionalized mesoporous TiO₂ possesses perfect anatase crystal structure and high surface area. The surface area of Fe-doped SH/TiO₂ mesoporous material is 4 times higher than that of P25. Based on the EPR results, it was found that trivalent Fe ions exist at low spin state and substitutes a part of Ti⁴⁺ ions into TiO₂ lattice. Fe-dropping in TiO₂ extends the adsorption band side of the resulting material to about 600 nm. Much high photocatalytic activity in the degradation of phenanthrene was obtained on the bifunctionalized mesoporous TiO₂ under visible light irradiation (λ > 420 nm), which is 6 times higher than that of pristine mesoporous TiO₂. The enhancement in the photocatalytic activity of bifunctionalized TiO₂ is ascribed to the extended absorption to visible light and strong interaction between SH-groups and PHE molecules.     

Preparation and characterization of TiO2 photocatalysts by Fe doping together with Au deposition for the degradation of organic pollutants

Fe³⁺ doped TiO₂ deposited with Au (Au/Fe–TiO₂) was successfully prepared with an attempt to extend light absorption of TiO₂ into the visible region and reduce the rapid recombination of electrons and holes. The samples were characterized by X-ray diffraction (XRD), N₂ physical adsorption, Raman spectroscopy, atomic absorption flame emission spectroscopy (AAS), UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra. The photocatalytic activities of the samples were evaluated for the degradation of 2,4-chlorophenol in aqueous solutions under visible light (λ > 420 nm) and UV light irradiation. The results of XRD, XPS and high-resolution transmission electron microscopy (HRTEM) analysis indicated that Fe³⁺ substituted for Ti⁴⁺ in the lattice of TiO₂, Au existed as Au⁰ on the surface of the photocatalyst and the mean particle size of Au was 8 nm. Diffuse reflectance measurements showed an extension of light absorption into the visible region for Au/Fe–TiO₂, and PL analysis indicated that the electron–hole recombination rate has been effectively inhibited when Au deposited on the surface of Fe-doped TiO₂. Compared with Fe doped TiO₂ sample and Au deposited TiO₂ sample, the Au/Fe–TiO₂ photocatalyst exhibited excellent visible light and UV light activity and the synergistic effects of Fe³⁺ and Au was responsible for improving the photocatalytic activity.     

Synthesis and visible‐light‐derived photocatalysis of titania nanosphere stacking layers prepared by chemical vapor deposition

BACKGROUND: In this study, visible‐light‐derived photocatalytic activity of metal‐doped titanium dioxide nanosphere (TS) stacking layers, prepared by chemical vapor deposition (CVD), was investigated. The as‐grown TS spheres, having an average diameter of 100–300 nm, formed a layer‐by‐layer stacking layer on a glass substrate. The crystalline structures of the TS samples were of anatase‐type. RESULTS: Ultraviolet (UV) absorption confirmed that metallic doping (i.e. Co and Ni) shifted the light absorption of the spheres to the visible‐light region. With increasing dopant density, the optical band gap of the nanospheres became narrower, e.g. the smallest band gap of Co‐doped TS was 2.61 eV. Both Ni‐ and Co‐doped TS catalysts showed a photocatalytic capability in decomposing organic dyes under visible irradiation. In comparison, Co‐doped TiO₂ catalyst not only displays the adsorption capacity, but also the photocatalytic activity higher than the N‐doped TiO₂ catalyst. CONCLUSION: This result can be attributed to the fact that the narrower band gap easily generates electron–hole pairs over the TS catalysts under visible irradiation, thus, leading to the higher photocatalytic activity. Accordingly, this study shed some light on the one‐step efficient CVD approach to synthesize metal‐doped TS catalysts for decomposing dye compounds in aqueous solution. Copyright © 2010 Society of Chemical Industry     

A Visible Light Photocatalyst of Carbonate‐Like Species Doped TiO2

Carbon‐doped TiO₂ nanomaterials have been successfully synthesized via an effective two‐step procedure involving hydrothermal method and followed by a low‐temperature calcination treatment process, through which a controllable amount of carbonate‐like species could be incorporated into TiO₂. First‐principles calculations suggest the TiO₂ doped with carbon in form of carbonate‐like species can effectively extend the adsorption of the material from ultraviolet region to visible light. And it is experimentally found that carbon‐doped TiO₂ nanomaterials exhibit much higher photocatalytic activity than reference P25 and TiO_2?xN_x catalysts toward the liquid‐phase degradation of organic pollutants under visible light (420 nm < λ < 800 nm) irradiation. The presence of synergic effect between carbonate‐like doping and anatase TiO₂ is believed to play an essential role in affecting the photocatalytic reactivity, and the response to the visible light is ascribed to the narrowed band gap energy controlled by carbon doping. Moreover, the roles of active species in the photocatalytic process are compared using different types of active species scavengers. Meanwhile, the degradation mechanism of the photocatalysis is proposed. It is hoped that our work could provide valuable information on the design of carbonate‐like doped semiconductor with more excellent properties and set the foundation for the further industrial application.     

Photocatalytic Degradation of Organic Dyes by a High Efficient TiO2-Based Catalysts Under Solar Light Irradiation

In this work, the Er³⁺:YAlO₃/Fe-doped TiO₂ composite, a high efficient TiO₂-based photocatalyst, was synthesized by ultrasonic dispersion and liquid boil methods. Among which, the Er³⁺:YAlO₃ is a kind of upconversion luminescence agent, which was prepared by nitrate-citric acid method. It can emit ultraviolet light under visible light excitation. The Er³⁺:YAlO₃/Fe-doped TiO₂ composite was characterized by X-ray diffraction and UV–vis spectral techniques. The degradation of Acid Red B dye was used to evaluate the photocatalytic activity of the Er³⁺:YAlO₃/Fe-doped TiO₂ composite under solar light irradiation. It was found that the photocatalytic activity of Er³⁺:YAlO₃/Fe-doped TiO₂ composite was much higher than that for the similar system with only Fe-doped TiO₂. And the influencing factors, such as Er³⁺:YAlO₃ content, irradiation time, initial concentration of Acid Red B, addition amount of Er³⁺:YAlO₃/Fe-doped TiO₂ and NaCl, on the photocatalytic degradation were also investigated. The Er³⁺:YAlO₃ as upconversion luminescence agent can elevate the photocatalytic activity of Fe-doped TiO₂ powder. Moreover, the Fe²⁺ ion can restrain the recombination of photogenerated electrons and holes. Thus, this Er³⁺:YAlO₃/Fe-doped TiO₂ composite is a useful material for the detoxification of wastewater because it can efficiently utilize solar light by converting visible light into ultraviolet light.     

Photoactive behavior of polyacrylonitrile fibers based on silver and zirconium co‐doped titania nanocomposites: Synthesis,characterization, and comparative study of solid‐phase photocatalytic self‐cleaning

Silver and zirconium co‐doped and mono‐doped titania nanocomposites were synthesized and deposited onto polyacrylonitrile fibers via sol–gel dip‐coating method. The resulted coated‐fibers were characterized by X‐ray diffraction (XRD), scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, diffuse reflectance spectroscopy, thermogravimetric analysis, and BET surface area measurement. Photocatalytic activity of the TiO₂‐coated and TiO₂‐doped coated fibers were determined by photomineralization of methylene blue and Eosin Y under UV–vis light. The progress of photodegradation of dyes was monitored by diffuse reflectance spectroscopy. The XRD results of samples indicate that the TiO₂, Ag‐TiO₂, Zr‐TiO₂, and Ag‐Zr‐TiO₂ consist of anatase phase. All samples demonstrated photo‐assisted self‐cleaning properties when exposed to UV–vis irradiation. Evaluated by decomposing dyes, photocatalytic activity of Ag–Zr co‐doped TiO₂ coated fiber was obviously higher than that of pure TiO₂ and mono‐doped TiO₂. Our results showed that the synergistic action between the silver and zirconium species in the Ag‐Zr TiO₂ nanocomposite is due to both the structural and electronic properties of the photoactive anatase phase. These results clearly indicate that modification of semiconductor photocatalyst by co‐doping process is an effective method for increasing the photocatalytic activity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Advanced Surface of Fibrous Activated Carbon Immobilized with FeO/TiO2 for Photocatalytic Evolution of Hydrogen under Visible Light

FeO-doped TiO₂ nanoparticle photocatalysts were immobilized onto the surface of fibrous activated carbon (ACF) via a sol-gel process. As an adsorbent and photocatalyst, FeO-TiO₂ on immobilized ACFs (FeO-TiO₂/ACF) greatly improved the photocatalysis rate of hydrogen production as compared with pure TiO₂ and ACF-TiO₂ under UV irradiation and visible light. The addition of ACFs surface significantly reduced the photogenerated pairs of electrons-hole recombination, thereby promoting the photocatalysis action of doped photo-metal oxides of FeO-TiO₂. Co-doping of FeO onto the lattice of the TiO₂ approach can improve the absorption activity of visible light through photo-metal oxide of TiO₂ and further enhance hydrogen production under visible light. The photocatalytic fabrics (FeO-TiO₂/ACF) were effortlessly split out from the experimental solution for re-utilization and exhibited high stability even after five complete regeneration cycles.     

Effect of concentration of Fe-dopant on the photoelectrochemical properties of Titania nanotube arrays

TiO₂ nanotubes have attracted great attention because of their photoelectrochemical activity. Metallic doping using a simple and rapid synthesizing approach can be a way to enhance this application. This paper describes a novel one-step anodization synthesis of Fe-doped TiO₂ nanotubes with various concentrations of iron doping. FESEM, XRD, and EDX were used to analyze the effect of doping concentration on the morphology, structure, and composition of the prepared samples respectively, and the results showed the formation of the anatase phase of TiO₂ nanotube arrays with Fe incorporation in the TiO₂ lattice. Although the Fe insertion in the TiO₂ lattice leads to better crystallinity, the non-uniformity in the morphology of doped samples suggests that adequate doping is required to maintain uniformity in the morphology. The absorption spectra of all the Fe-doped TiO₂ samples showed a red shift in their absorption edges compared to pristine TiO₂. This shift was observed more in the samples with higher doping concentrations. The photocurrent density of Fe-doped samples was observed to be significantly higher than that of the pristine TiO2 sample. This improvement was found to be concentration-dependent, with the best results being obtained from a sample doped at a level of 0.5%. The samples also showed high photostability, which, together with the increased photocurrent density, points to Fe-doped TiO₂ as a promising photoanode material.     

TiO2 nanofibers doped with rare earth elements and their photocatalytic activity

In the present study rare earth doped (Ln³⁺–TiO₂, Ln = La, Ce and Nd) TiO₂ nanofibers were prepared by the sol–gel electrospinning method and characterized by XRD, SEM, EDX, TEM, and UV-DRS. The photocatalytic activity of the samples was evaluated by Rhodamine 6G (R6G) dye degradation under UV light irradiation. XRD analysis showed that all the synthesized pure and doped titania nanofibers contain pure anatase phase at 500 °C but at 700 °C it shows both anatase and rutile phase. XRD result also shows that Ln³⁺-doped titania probably inhibits the phase transformation. The diameter of nanofibers for all samples ranges from 200 to 700 nm. It was also observed that the presence of rare-earth oxides in the host TiO₂ could decrease the band gap and accelerate the separation of photogenerated electron–hole pairs, which eventually led to higher photocatalytic activity. To sum up, our study demonstrates that Ln³⁺-doped TiO₂ samples exhibit higher photocatalytic activity than pure TiO₂ whereas Nd³⁺-doped TiO₂ catalyst showed the highest photocatalytic activity among the rare earth doped samples.     

Visible light photocatalytic activity of TiO2/heat‐treated PVC film

BACKGROUND: Semiconductor TiO₂ has been investigated extensively due to its chemical stability, nontoxicity and inexpensiveness. However, the wide band gap of anatase TiO₂ (about 3.2 eV) only allows it to absorb UV light. TiO₂ nanoparticles modified by conditional conjugated polymers show excellent photocatalytic activity under visible light. However, these conjugated polymers are not only expensive, but also difficult to process. Polyvinyl chloride (PVC) was heat‐treated at high temperature to remove HCl and a C?C conjugated chain structure was obtained. When TiO₂ nanoparticles were dispersed into the conjugated polymer film derived from PVC, this composites film exhibited high visible light photocatalytic activity. RESULTS: The photocatalytic activity of TiO₂/heat‐treated PVC (HTPVC) film was investigated by degrading Rhodamine B (RhB) under visible light irradiation. The photodegradation of RhB follows apparent first‐order kinetics. The rate constants of RhB photodegradation in the presence of the TiO₂/HTPVC films with different mass content of TiO₂ are 16–56 and 4–14 times that obtained in the presence of the pure HTPVC and TiO₂/polymethyl methacrylate (PMMA) composite film, respectively. The TiO₂/HTPVC film showed excellent photocatalytic activity and stability after 10 cycles under visible light irradiation. CONCLUSION: TiO₂/HTPVC film exhibits high visible light photocatalytic activity and stability. Copyright © 2012 Society of Chemical Industry     

Photocatalytic degradation of dyestuff wastewater under visible light irradiation using micron‐sized mixed crystal TiO2 powders

A phase transformation of micron‐sized TiO₂ powder from anatase to rutile was attempted by heat‐treatment in order to generate a new mixed crystal TiO₂ with high associated photocatalytic activity. Heat‐treated micron‐sized TiO₂ powders at different transition stages were characterized by X‐ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT‐IR) and transmission electron microscopy (TEM) methods. The tests of photocatalytic activity of the heat‐treated micron‐sized TiO₂ powders were conducted by the photocatalytic degradation of Rhodamine B and Acid Red B under visible light irradiation. The results indicate that mixed crystal TiO₂ photocatalyst heat‐treated at 400 °C for 60 min shows the highest photocatalytic activity. It can effectively decompose the Rhodamine B and Acid Red B in aqueous solution after 6 h visible light irradiation. A remarkable improvement in photocatalytic activity of TiO₂ is caused by the formation of combined rutile–anatase phases and separation of photogenerated electron–hole pairs. Copyright © 2007 Society of Chemical Industry     

Visible light induced self-cleaning performance of iron-doped TiO2 nanoparticles for surface applications

This study aimed to enhance the visible light photosensitivity of TiO₂ nanoparticles for self-cleaning applications by doping with Fe³⁺. Nanocrystalline undoped and Fe-doped TiO₂ (Ti_1 − xFe_xO₂, x = .01–.04) were synthesized via sol–gel method. The results demonstrated that Fe-doped TiO₂ nanoparticles exhibited visible light sensitivity and self-cleaning properties. An increased Fe concentration resulted in a red shift in the absorption band edge. Fe_0.03-doped TiO₂ with an average particle size of ∼21 nm, a crystallite size of ∼12 nm, and a band gap of ∼2.86 eV showed the highest photocatalytic activity (60% methylene blue degradation) and super-hydrophilicity (water droplet contact angle 9°) under visible light radiation. These findings highlight the potential of Fe-doped TiO₂ nanoparticles as a promising material for self-cleaning applications.     

The Synthesis and Photocatalytic Properties of Nitrogen Doped TiO<Subscript>2</Subscript> Films Prepared Using the AC-PLD Method

Synthesis of N doped TiO₂ films were conducted by the atmospheric controlled pulsed laser deposition (AC-PLD) method to generate visible light active photocatalytic films. In this method, the anion doped TiO₂ films were synthesized on a quartz substrate by the irradiation of a pulsed Nd:YAG laser on a TiO₂ target in the presence of gaseous nitrogen containing reagents at reduced pressure. For nitrogen doping, the use of CH₃CN was found to be more effective than the use of NH₃. The visible light absorption properties of the films were very sensitive to the CH₃CN partial pressure during ablation. When using CH₃CN, nitrogen and an equal quantity of carbon was uniformly doped into the TiO₂ films. The resultant films showed better catalytic performance than those which were either un-doped or doped using NH₃. The formation of nitrogen doped TiO₂ is discussed by relating experimental results to thermodynamic considerations. It is also suggested that stronger reducing agents such as carbon are required for doping nitrogen into TiO₂ films.     

Fabrication of high-efficiency anatase TiO2 photocatalysts using electrospinning with ultra-violet treatment

In metal oxide nanofiber fabrication using the electrospinning method, heat treatment is performed at temperatures of 500°C or higher for crystallization and polymer desorption. Therefore, it is difficult to fabricate low-temperature phase metal oxides that crystallize at low temperatures. TiO₂, a representative metal oxide often used as photocatalysts, is known to have higher photocatalytic activity in the low-temperature phase (anatase structure) than in the high-temperature phase (rutile structure). Studies on the fabrication of TiO₂ anatase nanofibers using conventional electrospinning have reported disadvantages such as the partial expression of rutile structures and low crystallinity. This study developed an anatase TiO₂ nanofiber as a high-efficiency catalyst based on the electrospinning method and a residual organic matter cleaning method that employs ultra-violet (UV) light. We fabricated nanofibers using the electrospinning method and implemented TiO₂ nanofibers with the anatase structure through heat treatment at 260°C. Residual organics remaining after heat treatment of the fabricated crystalized TiO₂ nanofibers were removed by exposing them to UV light, thereby improving photocatalytic efficiency. The photocatalytic efficiency of the fabricated TiO₂ nanofibers was confirmed through a methylene blue (MB) decomposition experiment under visible light irradiation. The photocatalytic efficiency (time taken for the concentration of the MB solution to reach 50%) of the UV-treated TiO₂ nanofibers was approximately six times higher than of P25 and the heat-treated nanofibers.     

In situ synthesis and enhanced visible light photocatalytic activity of C-TiO2 microspheres/carbon quantum dots

TiO₂ microspheres and TiO₂/carbon quantum dots (CQDs) composites with different CQDs contents were successfully synthesized via solvothermal and in situ hydrothermal method. The structure and morphology of the prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM). Results showed that carbon elements were successfully doped into the TiO₂ lattice (C-TiO₂) and CQDs were hybrid with C-TiO₂ microspheres. The X-ray photoelectron spectroscope (XPS), valence band XPS (VB-XPS) and UV–vis diffuse reflectance spectra (DRS) analyses revealed that carbon doped into TiO₂ microspheres could lead to local energy levels in the band structure and generate valence band tails to absorb visible light. The photocatalytic activities of these samples were evaluated by the photodegradation of Rhodamine B (RhB) under visible light irradiation. C-TiO₂/CQDs samples presented an enhanced photocatalytic performance compared with pristine TiO₂, which could be attributed to the present of CQDs, acting as adsorption sites for RhB molecules and charge separation centers to impede the recombination and prolong the life time of electron and hole pairs.     

Photocatalytic activity of undoped and sulfur-doped TiO2 films grown by MOCVD for water treatment under visible light

Titanium dioxide ceramic coatings have been used as catalysts in green technologies for water treatment. However, without the presence of a dopant, its photocatalytic activity is limited to the ultraviolet radiation region. The photocatalytic activity and the structural characteristics of undoped and sulfur-doped TiO₂ films grown at 400 °C by metallorganic chemical vapor deposition (MOCVD) were studied. The photocatalytic behavior of the films was evaluated by methyl orange dye degradation under visible light. The results suggested the substitution of Ti⁴⁺ cations by S⁶⁺ ions into TiO₂ structure of the doped samples. SO₄^2? groups were observed on the surface. S-TiO₂ film exhibited good photocatalytic activity under visible light irradiation, and the luminous intensity strongly influences the photocatalytic behavior of the S-TiO₂ films. The results supported the idea that the sulfur-doped TiO₂ films grown by MOCVD may be promising catalysts for water treatment under sunlight or visible light bulbs.     

Promoting Photocatalytic Cleaning Efficiency of Textile Finishing Solutions with Nanoboron as a p-Type Dopant

Boron is a commonly used p-type dopant for semiconductor and photonic applications. In this study, standard photocatalytic titanium dioxide (TiO₂) particles were doped with nanosized boron particles and coated on textiles to bring the photocatalytic light intensity closer to the visible light range. Boron/titania nanoparticle composites were initially prepared in DI water solutions and studied for their photocatalytic response through a statistical central composite design. To determine the most effective titania and nanoboron particle blend for photocatalytic textile coating, absorbance and stain bleach analyses were performed by UV light exposure. The performance of the composite particles at the optimal concentration has also been evaluated in the finishing solution and compared with the performances of the pure titania particles. It was found that the textiles coated with 0.08 wt% anatase doped with 0.16 wt% nanoboron as a p-type dopant provided improvement in self-cleaning ability under the visible light range in the DI water environment. Energy band gap calculations further verified the nanoboron-doped titania blend to have a lower energy barrier as compared with the 0.1 wt% anatase in agreement with the photocatalytic activity improvements. Nanoboron is shown to be a strong candidate as a p-type dopant to titania for photocatalytic textile coatings.