TiO2/BiVO4, a Heterojuncted Microfiber with Enhanced Photocatalytic Performance for Methylene Blue under Visible Light Irradiation

Novel TiO₂/BiVO₄ microfiber heterojunctions were constructed using cotton as biomorphic templates. The as-synthesized samples were characterized by scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectra and photocatalytic experiment. The morphology of the as-synthesized TiO₂/BiVO₄ composites was consisted of a large quantity of microfiber structures with diameter from 2.5 μm to 5 μm, and the surface of samples became more coarse and compact with the increase of weight ratio of TiO₂. The TiO₂/BiVO₄ samples with proper content (10.00wt%) showed the highest pho-tocatalytic degradation activity for methylene blue (MB) degradation among all the samples under visible light, and 88.58%MB could be degraded within 150 min. The enhancement of photocatalytic activity was mainly attributed to the formation of n-n heterojunction at the contact interface of TiO₂ and BiVO₄, which not only narrowed the band gap of BiVO₄ for extending the absorption range of visible light, but also promoted the transfer of charge carriers across interface. A possible photodegradation mechanism of MB in the presence of TiO₂/BiVO₄ microfibrous photocatalyst was proposed.     

Hydrothermal Preparation and Characterization of TiO2/BiVO4 Composite Catalyst and its Photolysis of Water to Produce Hydrogen

In the present work, bismuth vanadate composited photocatalysts were synthesized and characterized. X‐ray diffractometry and Raman results showed that the particles were well crystallized, and formed by the complex of monoclinic BiVO₄ and TiO₂. On electron microscopy, the photocatalyst exhibited high crystallization, agglutination and irregular shape, and was surrounded by numerous TiO₂ particles. The study of surface areas showed that the specific surface area of 30‐BiVO₄/TiO₂ composited was 112 m²·g^?1, which was nearly 10 times that of pure BiVO₄. The ultraviolet–visible diffuse reflectance spectra indicated the composited photocatalyst were activated in visible light. The activity of photocatalytic water splitting was studied. The results showed that monomer BiVO₄ photocatalyst was not able to produce hydrogen under any light source. BiVO₄/TiO₂ composited photocatalysts, however, were capable of generating hydrogen. Under UV light irradiation for 120 min, 1 g catalyst dispersed in 50 mL deionized water produced almost 1 mL hydrogen, such that the productivity of hydrogen was higher than that of P25‐TiO₂. Photocatalytic decomposition of water under visible light also confirmed that the BiVO₄/TiO₂ composited photocatalyst had the ability of water splitting.     

Photodegradation of Rhodamine B on Sulfur Doped ZnO/TiO2 Nanocomposite Photocatalyst under Visible-light Irradiation

Sulfur doped ZnO/TiO₂ nanocomposite photocatalysts were synthesized by a facile sol‐gel method. The structure and properties of catalysts were characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), UV‐vis diffusive reflectance spectroscopy (DRS) and N₂ desorption‐adsorption isotherm. The XRD study showed that TiO₂ was anatase phase and there was no obvious difference in crystal composition of various S‐ZnO/TiO₂. The XPS study showed that the Zn element exists as ZnO and S atoms form SO^2?₄. The prepared samples had mesoporosity revealed by N₂ desorption‐adsorption isotherm result. The degradation of Rhodamine B dye under visible light irradiation was chosen as probe reaction to evaluate the photocatalytic activity of the ZnO/TiO₂ nanocomposite. The commercial TiO₂ photocatalyst (Degussa P25) was taken as standard photocatalyst to contrast the prepared different photocatalyst in current work. The improvement of the photocatalytic activity of S‐ZnO/TiO₂ composite photocatalyst can be attributed to the suitable energetic positions between ZnO and TiO₂, the acidity site caused by sulfur doping and the enlargement of the specific area. S‐3.0ZnO/TiO₂ exhibited the highest photocatalytic activity under visible light irradiation after Zn amount was optimized, which was 2.6 times higher than P25.     

Preparation and characterization of nitrogen-doped TiO2 photocatalyst in different acid environments

Nitrogen-doped TiO₂ powders were successfully prepared by a wet method, i.e., a micro-emulsion-hydrothermal method, in different acid environments. Several characterization techniques, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse reflectance spectra, were combined to determine the crystal phase, concentration and chemical states of the nitrogen doped in TiO₂. The high photocatalytic activity of the nitrogen-doped TiO₂ was evaluated through the decomposition of rhodanmine B under visible light irradiation. It was suggested that the doped nitrogen formed oxynitride (NO) and produced impurity states at higher above the valence band of TiO₂. Therefore, the nitrogen doping could enhance the response of photocatalyst to the visible light and improve the photocatalytic activity because of the narrowing of band gap of TiO₂.     

Preparation of BiVO4/MIL‐125(Ti) composite with enhanced visible‐light photocatalytic activity for dye degradation

Because of their desired features, including very specific surface areas and designable framework architecture together with their possibility to be functionalized, Metal Framework (MOF) is a promising platform for supporting varied materials in respect of catalytic applications in water treatment. In this work, a novel visible‐light‐responsive photocatalyst that comprised BiVO₄ together with MIL‐125(Ti), was synthesized by a two‐step hydrothermal approach. The characterization of as‐obtained samples as performed by X‐ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, Fourier transform infrared spectroscope, X‐ray photoelectron spectroscopy and ultraviolet‐visible diffuse reflection spectra. Rhodamine B was selected being a target for the evaluation of the photocatalytic function of as‐developed photocatalyst. The photocatalytic reaction parameters, for example, the content of BiVO₄ as well as initial concentration of Rhodamine B was researched. The composite photocatalyst possessing Bi:Ti molar ratio of 3:2 brought to light the fact that the greatest photocatalytic activity had the ability to degrade 92% of Rhodamine B in 180 min. In addition to that, the BiVO₄/MIL‐125(Ti) composite could keep its photocatalytic activity during the recycling test. The phenomenon of disintegration of the photo‐generated charges in the BiVO₄/MIL‐125(Ti) composite was brought to discussion as well.     

TiO2/Cu2O Core/Ultrathin Shell Nanorods as Efficient and Stable Photocatalysts for Water Reduction

P‐type Cu₂O has been long considered as an attractive photocatalyst for photocatalytic water reduction, but few successful examples has been reported. Here, we report the synthesis of TiO₂ (core)/Cu₂O (ultrathin film shell) nanorods by a redox reaction between Cu²⁺ and in‐situ generated Ti³⁺ when Cu²⁺‐exchanged H‐titanate nanotubes are calcined in air. Owing to the strong TiO₂‐Cu₂O interfacial interaction, TiO₂ (core)/Cu₂O (ultrathin film shell) nanorods are highly active and stable in photocatalytic water reduction. The TiO₂ core and Cu₂O ultrathin film shell respectively act as the photosensitizer and cocatalyst, and both the photoexcited electrons in the conduction band and the holes in the valence band of TiO₂ respectively transfer to the conduction band and valence band of the Cu₂O ultrathin film shell. Our results unambiguously show that Cu₂O itself can act as the highly active and stable cocatalyst for photocatalytic water reduction.     

Electron Transfer in Dye‐Sensitised Semiconductors Modified with Molecular Cobalt Catalysts: Photoreduction of Aqueous Protons

A visible‐light driven H₂ evolution system comprising of a Ru^II dye ( RuP ) and Co^III proton reduction catalysts ( CoP ) immobilised on TiO₂ nanoparticles and mesoporous films is presented. The heterogeneous system evolves H₂ efficiently during visible‐light irradiation in a pH‐neutral aqueous solution at 25 °C in the presence of a hole scavenger. Photodegradation of the self‐assembled system occurs at the ligand framework of CoP , which can be readily repaired by addition of fresh ligand, resulting in turnover numbers above 300 mol H₂ (mol CoP )^?1 and above 200,000 mol H₂ (mol TiO₂ nanoparticles)^?1 in water. Our studies support that a molecular Co species, rather than metallic Co or a Co‐oxide precipitate, is responsible for H₂ formation on TiO₂. Electron transfer in this system was studied by transient absorption spectroscopy and time‐correlated single photon counting techniques. Essentially quantitative electron injection takes place from RuP into TiO₂ in approximately 180 ps. Thereby, upon dye regeneration by the sacrificial electron donor, a long‐lived TiO₂ conduction band electron is formed with a half‐lifetime of approximately 0.8 s. Electron transfer from the TiO₂ conduction band to the CoP catalysts occurs quantitatively on a 10 μs timescale and is about a hundred times faster than charge‐recombination with the oxidised RuP . This study provides a benchmark for future investigations in photocatalytic fuel generation with molecular catalysts integrated in semiconductors.     

Photoinduced charge property of Ag‐TiO2 films and its relationships with photocatalytic activity under visible illumination

In this article, TiO₂ films were synthesized by traditional spin coating method. To improve their photocatalytic activities, we deposited silver on these films by photodeposition. These films also were characterized by several testing techniques, such as X‐ray diffraction, ultraviolet–visible diffuse reflection spectrum, XPS, Raman spectroscopy (Raman), surface photovoltage spectroscopy, and SEM. The activity of different films was evaluated for degrading rhodamine B solution under visible illumination. The effects of AgNO₃ solution concentration on photoinduced charge property and photocatalytic activity were investigated. The results show that the Ag‐TiO₂ film immersed in 10^?3 mol·L^?1 AgNO₃ solution exhibits higher activity, which is in good agreement with the characterization results. The weaker the surface photovoltage spectroscopy signal, the higher the photocatalytic activity. Moreover, the activity of some films is higher than that of international Degussa P‐25 TiO₂ under visible illumination. Copyright © 2012 John Wiley & Sons, Ltd.     

Simulated Sunlight-Driven Degradation of Rhodamine B by Porous Peanut-Like TiO2/BiVO4 Composite

Porous peanut-like TiO₂/BiVO₄ composite nanostructures were synthesized via a template-free hydrothermal process with bismuth nitrate, ammonium metavanadate and anatase TiO₂ as raw materials. The crystal structures, morphologies, and optical properties of the as-prepared samples were characterized by X-ray powder diffraction, transmission electron microscope, scanning electron microscopy, X-ray photoelectron spectroscopy and UV–visible absorption spectra. Simulated sun-light induced photocatalytic degradation of Rhodamine B by porous peanut-like TiO₂/BiVO₄ nanostructures in the absence and presence of H₂O₂ has been investigated, and the results show these porous composite nanostructures with higher photocatalytic activity than pure BiVO₄ and anatase TiO₂. When TiO₂/BiVO₄ heterostructures were used as the photocatalysts under simulated sun-light irradiation, BiVO₄ could act as a sensitizer to absorb the visible light. Meanwhile, coupling different band-gap semiconductors of TiO₂ and BiVO₄, the compound facilitate separation of the photogenerated carriers under the internal field induced by the different electronic band structures of semiconductors.     

Toward photocatalytic hydrogen generation over BiVO_4 by controlling particle size

Owing to excellent light absorption and high activity fo r oxygen evolution,monoclinic bismuth vanadate(BiVO_4) is regarded as an ideal candidate for photocatalytic water splitting.However,its application is limited by the large particle size in micrometer scale,as well as the slightly positive conduction band.In this work,we successfully synthesized nano-BiVO_4 with particle size ranged from 27 nm to 57 nm by wet chemical method based on electrostatic spinning method.Unlike bulk BiVO_4,the nano-sized BiVO_4 possesses the ability to generate hydrogen by water splitting,and the activity could reach up to1.66 μmol h~(-1) g~(-1) with the assistance of Pt.The enhanced activity is mainly attributed to the improvements resulted from reduced particle size,which includes elevated conduction band,enlarged specific surface area and promoted charge separation.This work provides a simple method for synthesizing photocatalyst with small particle size and high yield.     

Understanding the synergistic effects,optical and electronic properties of ternary Fe/C/S‐doped TiO2 anatase within the DFT + U approach

Although TiO₂ is an efficient photocatalyst, its large band gap limits its photocatalytic activity only to the ultraviolet region. An experimentally synthesized ternary Fe/C/S‐doped TiO₂ anatase showed improved visible light photocatalytic activity. However, a theoretical study of the underlying mechanism of the enhanced photocatalytic activity and the interaction of ternary Fe/C/S‐doped TiO₂ has not yet been investigated. In this study, the defect formation energy, electronic structure and optical property of TiO₂ doped with Fe, C, and S are investigated in detail using the density functional theory + U method. The calculated band gap (3.21 eV) of TiO₂ anatase agree well with the experimental band gap (3.20 eV). The defect formation energy shows that the co‐ and ternary‐doped systems are thermodynamically favorable under oxygen‐rich condition. Compared to the undoped TiO₂, the absorption edge of the mono‐, co‐, and ternary‐doped TiO₂ is significantly enhanced in the visible light region. We have shown that ternary doping with C, S, and Fe induces a clean band structure without any impurity states. Moreover, the ternary Fe/C/S‐doped TiO₂ exhibit an enhanced photocatalytic activity, a smaller band gap and negative formation energy compared to the mono‐ and co‐doped systems. Moreover, the band edges of Fe/C/S‐doped TiO₂ align well with the redox potentials of water, which shows that the ternary Fe/C/S‐doped TiO₂ is promising photocatalysts to split water into hydrogen and oxygen. These findings rationalize the available experimental results and can assist the design of TiO₂‐based photocatalyst materials.     

Microwave‐Hydrothermal Preparation and Visible‐Light Photoactivity of Plasmonic Photocatalyst Ag‐TiO2 Nanocomposite Hollow Spheres

Visible‐light‐driven plasmonic photocatalyst Ag‐TiO₂ nanocomposite hollow spheres are prepared by a template‐free chemically‐induced self‐transformation strategy under microwave‐hydrothermal conditions, followed by a photochemical reduction process under xenon lamp irradiation. The prepared samples are characterized by using scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, N₂ adsorption‐desorption isotherms, X‐ray photoelectron spectroscopy, UV/Vis and Raman spectroscopy. Production of ?OH radicals on the surface of visible‐light illuminated TiO₂ was detected by using a photoluminescence method with terephthalic acid as the probe molecule. The photocatalytic activity of as‐prepared samples was evaluated by photocatalytic decolorization of Rhodamine B (RhB) aqueous solution at ambient temperature under visible‐light irradiation. The results show that the surface plasmon absorption band of the silver nanoparticles supported on the TiO₂ hollow spheres was red shifted, and a strong surface enhanced Raman scattering effect for the Ag‐TiO₂ nanocomposite sample was observed. The prepared nanocomposite hollow spheres exhibits a highly visible‐light photocatalytic activity for photocatalytic degradation of RhB in water, and their photocatalytic activity is higher than that of pure TiO₂ and commercial Degussa P25 (P25) powders. Especially, the as‐prepared Ag‐TiO₂ nanocomposite hollow spheres at the nominal atomic ratio of silver to titanium ( R ) of 2 showed the highest photocatalytic activity, which exceeds that of P25 by a factor of more than 2.     

Photocatalytic performance of silver-modified TiO2 embedded in poly(ethyl-acrylate-co-methyl metacrylate) matrix

The plasmonic Ag-TiO₂ (with 0.5 wt% Ag) photocatalyst was prepared on P25 TiO₂ surface. The presence of AgNPs on the titania was indicated by the UV–vis spectrum, which showed a plasmonic absorbance band in the visible range (λ _max?=?455 nm). XPS measurements suggested that Ag was in metallic (Ag) and in oxide forms on TiO₂. Ag-TiO₂ photocatalyst and TiO₂ were embedded in [poly(ethyl acrylate-co-methyl methacrylate; p(EA-co-MMA)] copolymer to attain mechanically stable, photocatalytically active nanocomposite films. The photooxidation of ethanol was slower on the photocatalyst/polymer nanocomposites, but it could be significantly improved by irradiating them with UV light. The photoaging was applied as a post-preparation treatment to improve the photocatalytic activity of the nanocomposite films. Changed surface morphology and the partial destruction of the polymer were supported by AFM and FTIR results. Contact angle measurements were used to determine the surface free energies of the prepared and the photoaged nanocomposite films.     

Synthesis and Modification of Zn‐doped TiO2 Nanoparticles for the Photocatalytic Degradation of Tetracycline

The synthesis of Zn‐doped TiO₂ nanoparticles by solgel method was investigated in this study, as well as its modification by H₂O₂. The catalyst was characterized by transmission electron microscopy, X‐ray diffraction, Brunauer–Emmett–Teller, UV–visible reflectance spectra and X‐ray photoelectron spectroscopy (XPS). The results indicated that doping Zn into TiO₂ nanoparticles could inhibit the transformation from anatase phase to rutile phase. Zn existed as the second valence oxidation state in the Zn‐doped TiO₂. Zn‐doped TiO₂ that was synthesized by 5% Zn doping at 450°C exhibited the best photocatalytic activity. Then, the H₂O₂ modification further enhanced the photocatalytic activity. Zn doping and H₂O₂ modifying narrowed the band gap and efficiently increased the optical absorption in visible region. The optimal degradation rate of tetracycline by Zn‐doped TiO₂ and H₂O₂ modified Zn‐doped TiO₂ was 85.27% and 88.14%. Peroxide groups were detected in XPS analysis of H₂O₂ modified Zn‐doped TiO₂, favoring the adsorption of visible light. Furthermore, Zn‐doped TiO₂ modified by H₂O₂ had relatively good reusability, exhibiting a potential practical application for tetracycline's photocatalytic degradation.     

Construction of immobilized films photocatalysts with CdS clusters decorated by metal Cd and BiOCl for photocatalytic degradation of tetracycline antibiotics

A kind of CdS/Cd-BiOCl immobilized films photocatalyst was prepared. The optical and physicochemical properties of the CdS/Cd-BiOCl photocatalysts were analysed, and the detailed characterization revealed CdS/Cd-BiOCl films photocatalyst with good charge carrier separation effect. The reusabilities and photocatalytic properties of the samples were studied. The 15%CdS/Cd-BiOCl photocatalyst exhibited superior performance in photocatalytic degradation of tetracycline (TC) and favorable stability under visible light irradiation. As for the photodegradation rate of TC, 15%CdS/Cd-BiOCl exhibited an excellent photodegradation activity, which is 4.06 and 9.53 times higher than that of CdS/Cd and BiOCl, respectively. The results showed that dominant active species are ^?O₂^? and ^?OH radicals during photodegradation. The charge transfer in Z-scheme CdS/Cd-BiOCl films photocatalyst could synchronously generate conduct band (CB) electrons in BiOCl and valence band (VB) holes in CdS, and metal Cd served as electron mediator. This work can be a reference for the design of film photocatalysts and new insight for photodegradating towards contaminants.     

BiVO4/TiO2 core-shell heterostructure: wide range optical absorption and enhanced photoelectrochemical and photocatalytic performance

In the present study, pristine BiVO₄, TiO₂ and BiVO₄/TiO₂ core-shell heterostructured nanoparticles are prepared by hydrothermal methods and studied for structural, morphological, optical, photoelectrochemical water splitting and photocatalytic degradation of methylene blue as an organic pollutant. Both pristine BiVO₄ and TiO₂ exhibit poor PEC and PC performance under visible light illumination. However, an enhanced PEC and PC activity in BiVO₄/TiO₂ core-shell heterostructure is observed due to high solar energy absorption and superior charge separation properties in core-shell nanoparticles. The photoelectrode prepared using BiVO₄/TiO₂ core-shell nanoparticles exhibit a photocathode behavior and produced cathodic photocurrent, however, the pristine BiVO₄ and TiO₂ photoelectrodes act as photoanode and produced anodic photocurrent. This behavior of change in current direction is also observe in the Mott-Schottky analysis where the BiVO₄/TiO₂ core-shell nanoparticles photoelectrode exhibits the positive slow showing p-type semiconducting behavior. The change in cathodic photoresponse in core-shell nanoparticles in comparison to anodic photoresponse of BiVO₄ and TiO₂ nanoparticles is explained in terms of the variations in the work function values. These results highlight the advantages of core-shell nanoparticle of suitable materials for photocatalytic and photoelectrochemical applications.     

Multi‐Electron Oxygen Reduction by a Hybrid Visible‐Light‐Photocatalyst Consisting of Metal‐Oxide Semiconductor and Self‐Assembled Biomimetic Complex

Adsorption experiments and density functional theory (DFT) simulations indicated that Cu(acac)₂ is chemisorbed on the monoclinic sheelite (ms)‐BiVO₄ surface to form an O₂‐bridged binuclear complex (OBBC/BiVO₄) like hemocyanin. Multi‐electron reduction of O₂ is induced by the visible‐light irradiation of the OBBC/BiVO₄ in the same manner as a blue Cu enzyme. The drastic enhancement of the O₂ reduction renders ms‐BiVO₄ to work as a good visible‐light photocatalyst without any sacrificial reagents. As a model reaction, we show that this biomimetic hybrid photocatalyst exhibits a high level of activity for the aerobic oxidation of amines to aldehydes in aqueous solution and imines in THF solution at 25 °C giving selectivities above 99 % under visible‐light irradiation.     

球形、花形和线状钒酸铋的可控合成及光催化性能

通过无模板、无助剂的可控水热法, 制备出球形、花形和线状钒酸铋(BiVO₄), 研究了其光学和可见光催化性能. 通过X射线衍射(XRD)和透射电镜(TEM)观测其结构和形貌特征. XRD谱线显示, 所制备的样品为单斜晶体结构. TEM结果表明, 通过控制水热过程的反应参数可以得到不同形貌的纳米粉体. 基于不同条件下制备的样品的微结构分析, 提出了这些不同形貌的形成机制. 紫外-可见漫反射光谱(UV-Vis DRS)表明BiVO₄样品的带隙能约为2.19-2.33 eV. 利用可见光(λ>420 nm)照射下的罗丹明B(RhB)降解实验评价了BiVO₄样品的光催化性能. 结果表明, BiVO₄的光催化活性比商用TiO₂催化剂P25 和掺氮TiO₂ (N-TiO₂)高得多. 所制备的球形BiVO₄光催化效率最高, 经可见光照射180 min, RhB溶液的降解率可达100%. 系统地研究了结构和形貌对不同pH值下制备的BiVO₄样品光催化活性的影响.     

Preparation,characterization and enhanced photocatalytic activity of Ni<Superscript>2+</Superscript> doped titania under solar light

Anatase TiO₂ was prepared by sol-gel method through the hydrolysis of TiCl₄. Ni²⁺ was doped into the TiO₂ matrix in the concentration range of 0.02 to 0.1 at.% and characterized by various analytical techniques. Powder X-ray diffraction revealed only anatase phase for all the samples, while diffuse reflectance spectral studies indicated a red shift in the band gap absorption to the visible region. The photocatalytic activities of these photocatalysts were probed for the degradation of methyl orange under natural solar light. The photocatalyst with optimum doping of 0.08 at.% Ni²⁺, showed enhanced activity, which is attributed to: (i) effective separation of charge carriers and (ii) large red shift in the band gap to visible region. The influence of crystallite size and dopant concentration on the charge carrier trapping — recombination dynamics is investigated.     

Cobalt-doped BiVO<Subscript>4</Subscript> (Co-BiVO<Subscript>4</Subscript>) as a visible-light-driven photocatalyst for the degradation of malachite green and inactivation of harmful microorganisms in wastewater

Co-doped BiVO₄, a visible-light-responsive photocatalytic semiconductor, was synthesized using a microwave hydrothermal method. The doped sample exhibited much higher photocatalytic activity for malachite green degradation under visible light irradiation than undoped BiVO₄. Similarly, improved inactivation efficiency toward Escherichia coli and Chlamydomonas pulsatilla (green tide) were observed with Co-doped BiVO₄. The degradation of malachite green by Co-doped BiVO₄ reaches 99% within 90 min irradiation to visible light. Similarly, the inactivation of Escherichia coli reaches 81.3% in 5 h and Chlamydomonas pulsatilla reaches 65.6% in 1 h irradiation to visible light. The enhanced photoactivity is believed to be due to the increment of the visible light absorption range by narrowing the band gap energy. In addition, the highly exposed reactive (010) facets can efficiently capture the photoinduced electrons, promote charge separation, and reduce recombination probability. Thus, these findings provide mechanistic insight into the effectiveness of Co-doped BiVO₄ semiconductors for the treatment of wastewater that contains industrial effluents and microorganisms.