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.     

Sonophotocatalytic treatment of diazinon using visible light‐driven Ce:Cu‐1,4‐BDOAH2 photocatalyst in a batch‐mode process: Response surface methodology and optimization

Cu–1,4‐benzenedioxyacetic acid (Cu‐1,4‐BDOAH₂) with a narrow band gap (2.52 eV) was synthesized and doped with Ce to afford Ce:Cu‐1,4‐BDOAH₂ as an efficient photocatalyst with narrower band gap (2.39 eV). The prepared Cu‐1,4‐BDOAH₂ and Ce:Cu‐1,4‐BDOAH₂ were characterized using Fourier transform infrared, energy‐dispersive X‐ray, diffuse reflectance spectroscopies, scanning electron microscopy and X‐ray diffraction. The sonophotocatalytic degradation of diazinon was carried out in a batch‐mode reactor using visible light‐driven Ce:Cu‐1,4‐BDOAH₂ photocatalyst as well as ultrasonic irradiation. The narrow band gap of the photocatalyst means that it can be activated under visible light illumination. The effects of operational parameters such as initial diazinon concentration (5–25 mg l^?1), pH (2–10), photocatalyst dosage (10–30 mg) and irradiation time (10–30 min) on the sonophotocatalytic degradation efficiency were investigated using central composite design under response surface methodology. The optimization process was studied using desirability function and the results indicated 99.8% degradation, which was obtained at optimum values of 25 mg l^?1, 6, 20 mg and 20 min for the initial concentration of diazinon, pH, photocatalyst dosage and irradiation time, respectively. Reusability experiments of Ce:Cu‐1,4‐BDOAH₂ photocatalyst showed that it is quite stable with excellent catalytic activity even after five cycles.     

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.     

Dimension‐Matched Zinc Phthalocyanine/BiVO4 Ultrathin Nanocomposites for CO2 Reduction as Efficient Wide‐Visible‐Light‐Driven Photocatalysts via a Cascade Charge Transfer

Cascade charge transfer was realized by a H‐bond linked zinc phthalocyanine/BiVO₄ nanosheet (ZnPc/BVNS) composite, which subsequently works as an efficient wide‐visible‐light‐driven photocatalyst for converting CO₂ into CO and CH₄, as shown by product analysis and ¹³C isotopic measurement. The optimized ZnPc/BVNS nanocomposite exhibits a ca. 16‐fold enhancement in the quantum efficiency compared with the reported BiVO₄ nanoparticles at the excitation of 520 nm with an assistance of 660 nm photons. Experimental and theoretical results show the exceptional activities are attributed to the rapid charge separation by a cascade Z‐scheme charge transfer mechanism formed by the dimension‐matched ultrathin (ca. 8 nm) heterojunction nanostructure. The central Zn²⁺ in ZnPc could accept the excited electrons from the ligand and then provide a catalytic function for CO₂ reduction. This Z‐scheme is also feasible for other MPc, such as FePc and CoPc, together with BVNS.     

BiVO4‐TiO2 Composite Photocatalysts for Dye Degradation Formed Using the SILAR Method

Composite photocatalyst films have been fabricated by depositing BiVO₄ upon TiO₂ via a sequential ionic layer adsorption reaction (SILAR) method. The photocatalytic materials were investigated by XRD, TEM, UV/Vis diffuse reflectance, inductively coupled plasma optical emission spectrometry (ICP‐OES), XPS, photoluminescence and Mott–Schottky analyses. SILAR processing was found to deposit monoclinic‐scheelite BiVO₄ nanoparticles onto the surface, giving successive improvements in the films′ visible light harvesting. Electrochemical and valence band XPS studies revealed that the prepared heterojunctions have a type II band structure, with the BiVO₄ conduction band and valence band lying cathodically shifted from those of TiO₂. The photocatalytic activity of the films was measured by the decolourisation of the dye rhodamine 6G using λ>400 nm visible light. It was found that five SILAR cycles was optimal, with a pseudo‐first‐order rate constant of 0.004 min^?1. As a reference material, the same SILAR modification has been made to an inactive wide‐band‐gap ZrO₂ film, where the mismatch of conduction and valence band energies disallows charge separation. The photocatalytic activity of the BiVO₄–ZrO₂ system was found to be significantly reduced, highlighting the importance of charge separation across the interface. The mechanism of action of the photocatalysts has also been investigated, in particular the effect of self‐sensitisation by the model organic dye and the ability of the dye to inject electrons into the photocatalyst′s conduction band.     

Z‐Scheme Photocatalytic Water Splitting on a 2D Heterostructure of Black Phosphorus/Bismuth Vanadate Using Visible Light

Spontaneously solar‐driven water splitting to produce H₂ and O₂, that is, the conversion of solar energy to chemical energy is a dream of mankind. However, it is difficult to make overall water splitting feasible without using any sacrificial agents and external bias. Drawing inspiration from nature, a new artificial Z‐scheme photocatalytic system has been designed herein based on the two‐dimensional (2D) heterostructure of black phosphorus (BP)/bismuth vanadate (BiVO₄). An effective charge separation makes possible the reduction and oxidation of water on BP and BiVO₄, respectively. The optimum H₂ and O₂ production rates on BP/BiVO₄ were approximately 160 and 102 μmol g^?1 h^?1 under irradiation of light with a wavelength longer than 420 nm, without using any sacrificial agents or external bias.     

Excellent photocatalytic reduction of nitroarenes to aminoarenes by BiVO4 nanoparticles grafted on reduced graphene oxide (rGO/BiVO4)

A novel heterogeneous composite material based on reduced graphene oxide (rGO) and bismuth vanadate (BiVO₄) was prepared and characterized by various techniques such as powder XRD, HRTEM, EADX, UV–Vis‐DRS, FT‐IR, Raman, BET and XPS analyses. The characterization results reveal that the rGO well decorated by BiVO₄. The electrochemical impedance spectroscopy (EIS) shows the increasing of charge transfer of rGO/BiVO₄ in presence of light irradiation. In this research, the pure BiVO₄ and rGO/BiVO₄ composite have been explored for photocatalytic reduction of nitroarenes. Among the prepared nanocomposites, rGO loaded with 10% BiVO₄ catalyst (noted as rGO/BiVO₄–10%) shows the best performance for the photo‐reduction of various nitroaromatic molecules to their corresponding amine compounds under visible‐light irradiation at room temperature. The catalyst exhibited in particular excellent photocatalytic activity for the conversion of 1,4‐dinitrobenzene to 4‐nitroanilline (100% conversion) in 20 min, 4‐chloronitrobenzene to 4‐chloroaniline and 2‐nitrophenol to 2‐aminophenol (100% conversion) in only 30 min. In addition, the conversion of 4‐bromonitrobenzene, 4‐iodonitrobenzene to their corresponding amine compounds (100% conversion) was achieved in 60 min. The catalyst was recovered for several times and reused without decreasing of its efficiency.     

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.     

Dip-coating deposition of resistive BiVO<Subscript>4</Subscript> thin film and evaluation of their photoelectrochemical parameters under distinct sources illumination

Resistive monoclinic bismuth vanadate (BiVO₄) nanocrystals in the form of thin films were obtained by the solution combustion synthesis coupled with the dip-coating deposition process. The structure, morphology, and optical properties of BiVO₄ nanocrystals were characterized by means of x-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis spectroscopy. The photoelectrochemical properties were obtained by cyclic voltammetry and chronoamperometry techniques in potassium chloride (KCl) electrolyte solution under distinct visible light sources irradiation condition. Under blue InGaN light emitting diode (LED) irradiation, the electrode has a better efficiency, faster response time (260 ms), and faster decay time (65 ms), when compared with the irradiation by dichroic lamp. Besides, the photocurrent density (j _ph) is approximately 39 times higher than j _ph obtained under dichroic lamp. The performance analysis based on the methylene blue degradation reaction has shown that the BiVO₄ material has higher electroactivity under InGaN LED irradiation condition, with estimated k _obs value of 200 × 10^?4 min^?1, which is a little higher than the value obtained with dichroic lamp illumination. In the dark condition, the BiVO₄ presented much lower photocatalytic activity.     

N‐Doped Yellow TiO2 Hollow Sphere‐Mediated Visible‐Light‐Driven Efficient Esterification of Alcohol and N‐Hydroxyimides to Active Esters

Herein we report a simple synthetic protocol for N‐doped yellow TiO₂ (N‐TiO₂) hollow spheres as an efficient visible‐light‐active photocatalyst using aqueous titanium peroxocarbonate complex (TPCC) solution as precursor and NH₄OH. In the developed strategy, the ammonium ion of TPCC and NH₄OH acts as nitrogen source and structure‐directing agent. The synthesized N‐TiO₂ hollow spheres are capable of promoting the synthesis of active esters of N‐hydroxyimide and alcohol through simultaneous selective oxidation of alcohol to aldehyde followed by cross‐dehydrogenative coupling (CDC) under ambient conditions upon irradiation of visible light. It is possible to develop a novel and cost‐effective one‐pot strategy for the synthesis of important esters and amides on gram scale using the developed strategy. The catalytic activity of N‐TiO₂ hollow spheres is much superior to that of other reported N‐TiO₂ samples as well as TiO₂ with varying morphology.     

Gold‐Nanoparticle‐Loaded Carbonate‐Modified Titanium(IV) Oxide Surface: Visible‐Light‐Driven Formation of Hydrogen Peroxide from Oxygen

Gold nanoparticle‐loaded rutile TiO₂ with a bimodal size distribution around 10.6 nm and 2.3 nm (BM‐Au/TiO₂) was prepared by the deposition precipitation and chemical reduction (DP‐CR) technique. Visible‐light irradiation (λ>430 nm) of the BM‐Au/TiO₂ plasmonic photocatalyst yields 35 μm H₂O₂ in aerated pure water at irradiation time (t_p)=1 h, and the H₂O₂ concentration increases to 640±60 μm by the addition of 4 % HCOOH as a sacrificing electron donor. Further, a carbonate‐modified surface BM‐Au/TiO₂ (BM‐Au/TiO₂‐CO₃^2?) generates a millimolar level of H₂O₂ at t_p=1 h with a quantum efficiency (Φ) of 5.4 % at λ=530 nm under the same conditions. The recycle experiments confirmed the stable performance of BM‐Au/TiO₂.     

四角星形BiVO4/Bi2O3催化剂的制备及性能

采用水热法合成具有四角星形貌的钒酸铋,再将钒酸铋浸渍在碱溶液里二次水热,制备出BiVO_4/Bi_2O_3催化剂。采用X射线粉末衍射(XRD)、扫描电子显微镜(SEM),紫外-可见漫反射(UV-Vis DRS)等方法对样品进行表征。可见光下,BiVO_4/Bi_2O_3复合物的光催化降解罗丹明B性能及光电流响应均优于纯BiVO_4。这是由于BiVO_4/Bi_2O_3复合材料形成了异质结构,有效抑制了光生电子与空穴的复合效率。     

四角星形BiVO4/Bi2O3催化剂的制备及性能研究

采用水热法合成具有四角星形貌的钒酸铋,再将钒酸铋浸渍在碱溶液里二次水热,制备出BiVO₄/Bi₂O₃催化剂。采用X射线粉末衍射(XRD)、扫描电子显微镜(SEM),紫外-射(UV-Vis DRS)等方法征。可见光下,BiVO₄/Bi₂O₃复合物的光催化降解丹明B性能及光电优于纯BiVO₄。BiVO₄/Bi₂O₃复合材料形成了异质结构,有效抑制了光电子与空穴的复合效率。     

Hydrothermal Synthesis of g‐C3N4/NiFe2O4 Nanocomposite and Its Enhanced Photocatalytic Activity

Herein, for the first time, a direct Z‐scheme g‐C₃N₄/NiFe₂O₄ nanocomposite photocatalyst was prepared using facile one‐pot hydrothermal method and characterized using XRD, FT‐IR, DRS, PL, SEM, EDS, TEM, HRTEM, XPS, BET and VSM characterized techniques. The result reveals that the NiFe₂O₄ nanoparticles are loaded on the g‐C₃N₄ sheets successfully. The photocatalytic activities of the as‐prepared photocatalysts were evaluated for the degradation of methyl orange (MO) under visible light irradiation. It was shown that the photocatalytic activity of the g‐C₃N₄/NiFe₂O₄ nanocomposite is about 4.4 and 3 times higher than those of the pristine NiFe₂O₄ and g‐C₃N₄ respectively. The enhanced photocatalytic activity could be ascribed to the formation of g‐C₃N₄/NiFe₂O₄ direct Z‐scheme photocatalyst, which results in efficient space separation of photogenerated charge carriers. More importantly, the as‐prepared Z‐scheme photocatalyst can be recoverable easily from the solution by an external magnetic field and it shows almost the same activity for three consecutive cycles. Considering the simplicity of preparation method, this work will provide new insights into the design of high‐performance magnetic Z‐scheme photocatalysts for organic contaminate removal.     

A New p‐Metal‐n Structure AgBr‐Ag‐BiOBr with Superior Visible‐Light‐Responsive Catalytic Performance

A novel visible‐light‐driven AgBr‐Ag‐BiOBr photocatalyst was synthesized by a facile hydrothermal method. Taking advantage of both p‐n heterojunctions and localized surface plasmon resonance, the p‐metal‐n structure exhibited a superior performance concerning degradation of methyl orange under visible‐light irradiation (λ>420 nm). A possible photodegradation mechanism in the presence of AgBr‐Ag‐BiOBr composites was proposed, and the radical species involved in the degradation reaction were investigated. HO₂^?/^?O₂^? played the same important role as ^?OH in the AgBr‐Ag‐BiOBr photocatalytic system, and both the electron and hole were fully used for degradation of organic pollutants. A dual role of metallic Ag in the photocatalysis was proposed, one being surface plasmon resonance and the other being an electron‐hole bridge. Due to the distinctive p‐metal‐n structure, the visible‐light absorption, the separation of photogenerated carriers and the photocatalysis efficiency were greatly enhanced.     

Visible‐Light‐Driven CO2 Reduction by Mesoporous Carbon Nitride Modified with Polymeric Cobalt Phthalocyanine

The integration of molecular catalysts with low‐cost, solid light absorbers presents a promising strategy to construct catalysts for the generation of solar fuels. Here, we report a photocatalyst for CO₂ reduction that consists of a polymeric cobalt phthalocyanine catalyst (CoPPc) coupled with mesoporous carbon nitride (mpg‐CN_x) as the photosensitizer. This precious‐metal‐free hybrid catalyst selectively converts CO₂ to CO in organic solvents under UV/Vis light (AM 1.5G, 100 mW cm^?2, λ>300 nm) with a cobalt‐based turnover number of 90 for CO after 60 h. Notably, the photocatalyst retains 60 % CO evolution activity under visible light irradiation (λ>400 nm) and displays moderate water tolerance. The in situ polymerization of the phthalocyanine allows control of catalyst loading and is key for achieving photocatalytic CO₂ conversion.     

ZnO/BiVO4-V2O5异质结构光生电荷性质及可见光下表面光电流行为

利用水热法合成了花状和球状ZnO微纳材料,并与硝酸铋和偏钒酸铵溶液体系反应构筑了ZnO/BiVO4-V2O5复合体系.利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)及X射线衍射(XRD)对材料进行了系统的表征.利用表面光伏(SPV)、表面光电流(SPC)和瞬态光伏(TPV)技术研究了ZnO/BiVO4-V2O5表面光生电荷的产生和传输机制.结果显示该复合材料在可见区产生了良好的光电响应,获得了较高的光生载流子的分离效率,光生电荷的寿命也同时增加.在单色弱可见光(波长500 nm)照射下,复合材料产生良好重复性的表面光电流响应.     

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.     

Selective Aerobic Oxidation of Primary Alcohols to Aldehydes over Nb2O5 Photocatalyst with Visible Light

Primary alcohols are selectively converted into aldehydes by using a Nb₂O₅ photocatalyst under visible‐light irradiation. A strong interaction between the alcohol and Nb₂O₅ generates a donor level within the forbidden band of Nb₂O₅, which provides a visible‐light‐harvesting ability. Over oxidation of aldehydes into carboxylic acids does not proceed under visible‐light irradiation.     

Visible‐Light‐Induced Photocatalytic Hydrogen Production over Binuclear RuII–Bipyridyl Dye‐Sensitized TiO2 without Noble Metal Loading

Highly efficient, visible light induced photocatalytic H₂ production was achieved over a TiO₂ system sensitized by binuclear Ru^II bipyridyl (bpy) complex [Ru₂(bpy)₄(BL)](ClO₄)₂ (BL=bridging ligand) without Pt loading, which is almost unaffected by pH in aqueous solution in the wide range from pH 5.00 to 10.50, although the dye molecules can only be loosely attached to TiO₂ due to the absence of terminal carboxyl groups. The photocatalyst shows remarkable long‐term stability and reproducibility of H₂ evolution even after exchanging the aqueous triethanolamine solution. The amount of H₂ evolved over 100 mg of photocatalyst in 27 h of irradiation corresponds to a turnover number of about 75 340, and the apparent quantum yields are estimated to be 16.8 and 7.3 % under 420 and 475 nm monochromatic light irradiation, respectively. A comparative study shows that the loosely attached dye [Ru₂(bpy)₄(BL)](ClO₄)₂ has higher photosensitization efficiency than tightly linked dyes with terminal carboxyl groups, such as [Ru₂(dcbpy)₄(BL)](ClO₄)₂ and N719. It can be rationalized by their different coordination, physicochemical, electron‐injection, and back‐transfer properties.