Enhanced photocatalytic properties of hierarchical nanostructured TiO_2 spheres synthesized with titanium powders

Using Ti powder as reagent, TiO 2 nanoneedle/nanoribbon spheres were prepared via hydrothermal method in NaOH solution. The samples were characterized by field emission scanning electron microscopy （FESEM）, transmission electron microscopy （TEM） with selected area electron diffraction （SAED）, X-ray diffraction （XRD）, and UV-visible light absorption spectrum. The results indicate that the growth orientations of the crystals are influenced by the hydrothermal temperature and NaOH concentration. The diameter of the nanoneedle spheres and nanoribbon spheres （40 50 μm） are almost the same as that of Ti powders. TiO 2 nanoneedle/nanoribbon sphere powders are anatase after heat treatment at 450 °C for 1 h. Furthermore, methyl orange was used as a target molecule to estimate the photocatalytic activity of the specimens. Under the same testing conditions, the photocatalytic activities of the products decrease in the following order： TiO 2 nanoneedle sphere, TiO 2 nanoribbon sphere and P25.

Appreciable Enhancement of Photocatalytic Performance for N-doped SrMoO_(4) via the Vapor-thermal Method

A series of nitrogen-doped SrMoO_(4) with different Sr/N mole ratio (R=0,0.05,0.10,0.15,0.20,0.40,and 0.60) were synthesized using urea as the N source via the vapor-thermal method.The photocatalytic degradation ability of all samples was evaluated using methylene blue (MB) as a target contaminant.The band gaps of N-doped samples are all higher than that of pristine ones,which is only 3.12 eV.BET specific surface area S_(BET) and pore volume are increased due to the N doping.And the greater increase of S_(BET),the faster the photodegradation speed of methylene blue on SrMoO_(4).More specifically,the degradation efficiency of MB is improved up to 87%in 100 min.

Fabrication and photocatalytic properties of Cu_2S/T-ZnO_w heterostructures via simple polyol process

The Cu2S/tetrapod-like ZnO whisker（T-ZnOw） heterostructures were successfully synthesized via a simple polyol process employing the poly（vinyl pyrrolidone）（PVP） as a surfactant.The as-prepared heterostructures were characterized by X-ray diffraction（XRD）,field emission scanning electron microscopy（FESEM）,X-ray photoelectron spectroscopy（XPS） and Fourier transform infrared（FTIR）.The photocatalytic properties of Cu2S/T-ZnOw nanocomposites synthesized with different PVP concentrations were evaluated by photodegradation of methyl orange（MO） under UV irradiation.The results show that the Cu2S/T-ZnOw nanocomposites exhibit remarkable improved photocatalytic property compared with the pure T-ZnOw.The sample prepared with 3.0 g/L PVP shows an excellent photocatalytic property and the highest photodegradation rate of MO is 97% after UV irradiation for 120 min.Besides,the photocatalytic activity of the photocatalyst has no evident decrease even after four cycles,which demonstrates that the Cu2S/T-ZnOw photocatalyst exhibits an excellent photostability.Moreover,the photocatalytic mechanism of the Cu2S/T-ZnOw nanocomposites was also discussed.

Enhanced Photocatalytic Properties of Silver Oxide Loaded Bismuth Vanadate

In this work, BiV04 powders were synthesized by a sol-gel method, and the BiV04 gels with different calcination temperature were investigated by X-ray diffraction （XRD）. Absorption range and band gap energy, which are respon- sible for the observed photocatalyst behavior, were investigated by UV/vis diffuse reflectance spectroscopy （DRS） for pure and silver oxide loaded BiV04. Pbotocatalytic properties of the prepared samples were examined by studying the degradation of the methyl orange. When using NaCI02 as an electron acceptor, the possible photocatalytic mech- anism has been discussed by photocatalytic reactions. With the help of electron acceptor, the results show clearly that the BiV04 loaded silver oxide exhibited superior photocatalytic activity in simulated dye wastewater treatment.

Synthesis,Structure,Photoluminescence and Photocatalytic Properties of a New Cd(Ⅱ)Metal-organic Framework Based on 1,4-Di(2,6-dimethyl-3,5-dicarboxypyridyl)benzene

A new 3D coordination polymer, [Cd2（L）（bpb）2]n（1, H4L = 1,4-di（2,6-dimethyl-3,5-dicarboxypyridyl） benzene, bpb = 1,4-bis（4-pyridyl） benzene, has been hydrothermally synthesized and characterized by single-crystal X-ray diffraction analysis, elemental analysis, TGA, IR spectroscopy and UV-Vis spectrum. Complex 1 crystallizes in orthorhombic, space group C2221, with a = 10.9393（12）, b = 20.900（3）, c = 20.027（2） A, β = 90°, V = 4578.9（9） A^3, Dc = 41.668 Mg/cm^3, Mr = 1149.74, F（000） = 2312.0, μ = 0.996 mm^（–1）, Z = 4, the final R = 0.0316 and wR = 0.0786 for 4271 observed reflections with I 〉 2σ（I）. Structural analysis shows that 1 possesses a 3D network based on the 2D layer bridged by L^4-ligands, while the 2D layers are composed of the adjacent 1D chains joined by L^4-ligand. The photoluminescent investigation indicates that one broad emission band with the maximum of 445 nm can be observed in 1. Moreover, compound 1 has high photocatalytic degradation effects on methylene blue under UV irradiation.

Synthesis and photocatalytic properties of InVO_4 sol containing nanocrystals by mild hydrothermal processing

The precursor precipitation of InVO4 was synthesized by co-precipitation using indium trichloride (InCl3), ammonium metavanadate (NH4VO3) and ammonia (NH3·H2O) as raw materials. The InVO4 sols with orthorhombic phase were obtained by hydrothermal treatment (the precursor precipitation solution at 423 K, for 4 h). The precursor and sol of InVO4 were characterized by X-ray diffraction (XRD), Fourier Transform Infra-red spectra (FT-IR), scanning electron microscopy (SEM) measurements. The XRD patterns indicate that the InVO4 precursor is amorphous phase, InVO4 sol contains orthorhombic InVO4 nanocrystals. The results also reveal that the pH value of the reaction mixture and reaction temperature play important roles to the target phase. InVO4-TiO2 thin films on glass slides were prepared by the dip-coating method from the composite sol. The photocatalytic properties of the InVO4-TiO2 thin films were investigated by the photocatalytic degradation of methyl orange solution. The results indicate that it has better photocatalytic activities than pure TiO2 thin films or pure InVO4 thin films with UV light.

Influence of Cadmium Doping on Structural, Optical, electrical and Photocatalytic Properties of TiOz Thin Films Prepared by Spray Pyrolysis Technique

Undoped and doped cadmuim titanium oxide thin films at different percentage （1, 3, 4, and 5）% were fabricated by spray pyrolysis by using a solution of titanium tetrachloride and ethyl alcohol. The films have been deposited on heated quartz substrates at 623 K. After annealing for 120 min at 823 K, the initially amorphous films became polycrystalline with a predominant anatase structure and average crystallite sizes depending on dopant Cd concentration. Atomic force microscope （AIM） results show that the addition of the Cd to TiO2 thin films become smooth. Optical study shows the optical band gap, and transmission has been increasing with increasing doping concentration in TiO2 thin films. The electrical resistivity is decreases with increasing doping concentration Cd in TiO2 thin films could be attributed to the increasing charge concentration. Photocatalytic activity of the TiO2 films were studied by monitoring the degradation of aqueous methylene blue under UV light irradiation and was observed that increasing doping concentration had good photocatalytic activity which was explained as due to the structural and morphological properties of the films.

Anisotropy of Photocatalytic Properties in Nanostructured Photocatalysts

Energy band engineering and the nature of surface/interface of a semiconductor play a significant role in searching high efficiency photocatalysts. Actually, the active facets, morphology controlling, especially the exposed facets modulation of photocatalysts during preparation are very desirable. In order to achieve high photocatalytic performance, intrinsic mechanism of such anisotropic properties should be fully considered. In this review, we mainly emphasis on the latest research developments of several extensively investigated photocatalysts and their anisotropic photocatalytic properties, as well as the correlation between effective masses anisotropy and photocatalytic properties. It will be helpful to understand the photocatalytic mechanism and promote rational development of photocatalyst for wide applications.

Development strategies and improved photocatalytic CO_(2) reduction performance of metal halide perovskite nanocrystals

In recent years,photocatalytic CO_(2)reduction reaction(CRR) has attracted much scientific attention to overcome energy and environmental issues by converting CO_(2)into high-value-added chemicals utilizing solar energy.Metal halide perovskite(MHP) nanocrystals(NCs) are recognized as an ideal choice for CRR owing to their outstanding optoelectronic properties.Although great efforts have been devoted to designing more effective photocatalysts to optimize CRR performance,severe charge recombination,instability,and unsatisfactory activity have become major bottlenecks in developing perovskite-based photocatalysts.In this review,we mainly focus on the recent research progress in the areas of relevance.First,a brief insight into reaction mechanisms for CRR and structural features of MHPs are introduced.Second,efficient modification approaches for the improvement of the photocatalytic activity and stability of the perovskite-based catalysts are comprehensively reviewed.Third,the state-of-the-art achievements of perovskite-based photocatalysts for CRR are systematically summarized and discussed,which are focused on the modification approaches,structure design,and the mechanism of the CO_(2)reduction process.Lastly,the current challenges and future research perspectives in the design and application of perovskite materials are highlighted from our point of view to provide helpful insights for seeking breakthroughs in the field of CRR.This review may provide a guide for scientists interested in applying perovskite-based catalysts for solar-to-chemical energy conversion.

LDH-based nanomaterials for photocatalytic applications:A comprehensive review on the role of bi/trivalent cations, anions,morphology, defect engineering, memory effect, and heterojunction formation

Using sunlight to drive chemical reactions via photocatalysis is paramount for a sustainable future.Among several photocatalysts,employing layered double hydrides(LDH) for photocatalytic application is most straightforward and desirable owing to their distinctive two-dimensional(2D) lamellar structure and optical attributes.This article reviews the advancements in bimetallic/trimetallic LDHs and various strategies to achieve high efficiency toward an outstanding performing photocatalyst.Firstly,the tuning of LDH components that control the electro nic and structural properties is explained.The tu ning obtained through the adoption,combination,and incorporation of different cations and anions is also explained.The progress of modification methods,such as the adoption of different morphologies,delamination,and defect engineering towards enhanced photocatalytic activities,is discussed in the mainstream.The band engineering,structural characteristics,and redox tuning are further deliberated to maximize solar energy harvesting for different photocatalytic applications.Finally,the progress obtained in forming hierarchical heterostructures through hybridization with other semiconductors or conducting materials is systematically disclosed to get maximum photocatalytic performance.Moreover,the structural changes during the in-situ synthesis of LDH and the stability of LDH-based photocatalysts are deliberated.The review also summarizes the improvements in LDH properties obtained through modification tactics and discusses the prospects for future energy and environmental applications.

Photoelectrocatalytic principles for meaningfully studying photocatalyst properties and photocatalysis processes:From fundamental theory to environmental applications

Photocatalysis is critically important for environmental remediation and renewable energy technologies.The ability to objectively characterize photocatalyst properties and photocatalysis processes is paramount for meaningful performance evaluation and fundamental studies to guide the design and development of high-performance photocatalysts and photocatalysis systems.Photocatalysis is essentially an electron transfer process,and photoelectrocatalysis(PEC)principles can be used to directly quantify transferred electrons to determine the intrinsic properties of photocatalysts and photocatalysis processes in isolation,without interference from counter reactions due to physically separated oxidation and reduction half-reactions.In this review,we discuss emphatically the PEC-based principles for characterizing intrinsic properties of photocatalysts and important processes of photocatalysis,with a particular focus on their environmental applications in the degradation of pollutants,disinfection,and detection of chemical oxygen demand(COD).An outlook towards the potential applications of PEC technique is given.

Mesh-Like Bi2MoO6 with Enhanced and Stable Visible Light Photocatalytic Activity

Mesh-like Bi2MoO6 product was successfully synthesized by a hydrothermal method without using any surfactant or template. The pH value played an important role in the formation of this morphology. The as-prepared mesh-like Bi2MoO6 sample exhibited excellent visible-light-driven photocatalytic e ciency. The photocatalytic activity of the mesh-like Bi2MoO6 sample was much higher than that of bulk Bi2MoO6 sample prepared by solid-state reac-tion. Di erence in the photocatalytic activities of the mesh-like Bi2MoO6 sample and bulk Bi2MoO6 sample was further investigated.

Photocatalytic performance of TiO_2 nanocrystals with/without oxygen defects

To investigate the role of oxygen defects on the photocatalytic activity of TiO2,the TiO2 nanocrystals with/without oxygen defects are successfully synthesized by the hydrothermal and sol‐gel methods,respectively.The as‐prepared TiO2 nanocrystals with defects are light blue and the absorption edge of light is towards the visible light region(~420 nm).Raman and X‐ray photoelectron spectroscopy(XPS)measurements all confirm that the concentration of oxygen vacancies in the TiO2 synthesized by the sol‐gel method is less than that synthesized through the hydrothermal route.The introduction of oxygen defects contributes to a new state in the band gap that narrows the band gap,which is the reason for the extension of light absorption into the visible light region.The photocurrent results confirm that this band‐gap narrowing enhances the photocurrent response under simulated solar light irradiation.The TiO2 with oxygen defects shows a higher photocatalytic activity for decomposition of a methylene blue solution compared with that of the perfect TiO2 sample.The photocatalytic mechanism is discussed based on the density functional theory calculations and photoluminescence spectroscopy measurements.

Effects of N Doping on the Microstructures and Optical Properties of TiO_2

TiO_2 nanopowders with different nitrogen(N) dopant concentrations were first synthesized by sol-gel method. XRD, TEM, HRTEM, XPS, UV-vis DRS were used to characterize the effects of N doping on the microstructures and optical properties of TiO_2. The results indicated that the prepared TiO_2 only contained anatase phase with a slight distortion, and the N doping improved the dispersity of TiO_2. The N doping leaded to more defects in TiO_2, capturing the charge carriers and inhibiting the combination of electrons and holes. Also, the N-doped TiO_2 was composed of Ti, O and N. Further, N was doped into the TiO_2 lattice by substituting for O, forming the oxidized nitrogen in the form of Ti–N–O or Ti–O–N bond, and Ti was present in the form of Ti^(4+) in TiO_2. Finally, the absorbance of N-doped TiO_2 was obviously improved in both UV and visible light region. Optical absorption edges of N-doped TiO_2 samples showed obvious red shift, which expanded spectral absorption range of TiO_2 and improved the utilization efficiency of visible light. It is concluded that N element was successfully doped into TiO_2 crystal lattice, and the N dopant concentration of 3.0% was designed to modify Ti O2.

A Novel 3D Metal Coordination Polymer Based on Tetranuclear Cobalt Cluster Building Blocks:Synthesis,Crystal Structure and Photocatalytic Property

A novel 3D MCP,[Co;（μ;-OH）(btc)（bmip）];(1,H;btc=1,3,5-benzenetricarboxylate acid,bmip=1,3-bis（2-methylimidazolyl）propane),was synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction,powder XRD,FT-IR,TGA and elemental analysis techniques.MCP 1 features a 3D framework based on tetranuclear Co（Ⅱ）clusters where the four cobalt ions are coplanar,and shows an unusual binodal（3,10）-connected topology.Furthermore,the photocatalytic experiment result indicates the degradation ratios of rhodamine B（RhB）reach 78.2%when MCP 1 acts as catalyst.

Photoluminescence behavior and visible light photocatalytic activity of ZnO,ZnO/ZnS and ZnO/ZnS/α-Fe_2O_3 nanocomposites

In order to achieve effective, economic, and easily achievable photocatalyst for the degradation of dye methyl orange（MeO）, ZnO, ZnO/ZnS and ZnO/ZnS/α-Fe2O3 nanocomposites were prepared by simple chemical synthetic route in the aqueous medium. Phase, crystallinity, surface structure and surface behavior of the synthesized materials were determined by X-ray diffraction（XRD） and Brunauer-Emmett-Teller analysis（BET） techniques. XRD study established formation of good crystalline ZnO, ZnO/ZnS and ZnO/ZnS/α-Fe2O3 nanomaterials. By using intensity of constituent peaks in the XRD pattern, the compositions of nanocomposites were determined. From the BET analysis, the prepared materials show mesoporous behavior, type Ⅳ curves along with H4 hysteresis. The ZnO/ZnS/α-Fe2O3 composite shows the largest surface area among three materials. From the UV-visible spectra, the band gap energy of the materials was determined. Photoluminescence spectra（PL） were used to determine the emission behavior and surface defects in the materials. In PL spectra, the intensity of UV peak of ZnO/ZnS is lowered than that of ZnO while in case of ZnO/ZnS/α-Fe2O3, the intensity further decreased. The visible emission spectra of ZnO/ZnS increased compared with ZnO while in ZnO/ZnS/α-Fe2O3 it is further increased compared with ZnO/ZnS. The as-synthesized materials were used as photocatalysts for the degradation of dye MeO. The photo-degradation data revealed that the ZnO/ZnS/α-Fe2O3 is the best photocatalyst among three specimens for the degradation of dye MeO. The decrease of intensity of UV emission peak and the increase of intensity of visible emission cause the decrease of recombination of electrons and holes which are ultimately responsible for the highest photocatalytic activity of ZnO/ZnS/α-Fe2O3.

Ionothermal Synthesis, Crystal Structure and Photocatalytic Property of a New Cobalt Coordination Polymer

The reaction of flexible bis（imidazole） ligand and 1,2-bis（imidazol-l＇-yl）methane （bimm） with Co（Ⅱ） salt under ionothermal method resulted in the formation of a new coordination polymer {[Co（bimm）3]·（PF6）2}n （1）. X-ray single-crystal diffraction determination reveals that 1 crystallizes in the triclinic Pi space group, with α = 8.647（6）, b = 12.092（9）, c = 14.967（1 l） A, α = 88.912（8）, β = 81.199（8）, ）, = 89.395（8）°, V= 1546 （2） A3, Z = 2, Mr = 793.39, Dc= 1.704 Mg/m3,μ = 0.768 mm-1 F（000） = 798, the final R = 0.0626 and wR = 0.1634 for 4319 observed reflections with I〉 2σ（I）. In compound 1, the Co（lI） ion is connected to another Co（ll） by two bimm ligands to form 1D double chains which are further linked by bimm ligands to form a 2D wavelike layer. Topologically, the structure of 1 represents a uninodal 2D 4-connected sq1/Shubnikov tetragonal plane net. Moreover, thermogravimetric analyses and photocatalytic property for 1 have also been investigated.

The Influence of Morphology on Photo-catalytic Activity and Optical Properties of Nanocrystalline ZnO Powder

ZnO nano-particles were synthesized via an ammonical ammonium carbonate solution by precipitation method in presence of some additives such as urea, oleic and stearic acid. The morphology and crystallinity of the obtained zinc oxide particles depend critically on the type of additive which was used. Additives also affected the crystal orientation of precipitate nano-particles. SEM, XRD, BET and UV-visible were used to characterize morphology, microstructure, specific surface area and optical properties of the products.Photo-catalysis properties of the as-prepared ZnO powders were evaluated by degradation of methyl red(acid red) in aqueous solution exposed to UV-light. Results suggested a close relationship among the morphology,size and surface area on photo-catalysis and optical properties of the particles. The widest Egvalue(3.56 e V),highest degradation and decolorization efficiency(99%) were obtained from a sample with the smallest grain size(largest surface area) which were used urea as an additive.

High photocatalytic activities of zinc oxide nanotube arrays modified with tungsten trioxide nanoparticles

Well‐aligned zinc oxide(ZnO)nanotube arrays loaded with tungsten trioxide(WO3)nanoparticles were synthesized by a process involving chemical bath deposition in combination with pyrolysis.The prepared ZnO–WO3composites were characterized by X‐ray diffraction,energy dispersive spectrometer,field emission scanning electron microscopy,X‐ray photoelectron spectroscopy,photoluminescence spectroscopy,Fourier transform infrared spectroscopy and UV–vis diffuse reflectance spectroscopy.The photocatalytic activities of the ZnO–WO3composite photocatalysts with different WO3contents for the degradation of the herbicide chlorinated phenoxyacetic acid(MCPA‐Na)under simulated sunlight irradiation were systematically evaluated.It was found that the WO3content had a great effect on the photocatalytic activity of the ZnO–WO3composites.The composite with3%WO3showed the highest photocatalytic activity,with a degradation rate of chlorinated phenoxyacetic acid of98.5%after200min with20mg of photocatalyst.This photodegradation rate was about twice that of the pristine ZnO nanotube array.The recombination of photogenerated electrons and holes was increasingly suppressed with the addition of WO3to ZnO.The high relative content of defects on the surface of the ZnO–WO3composites was beneficial to their photocatalytic activity in the degradation of chlorinated phenoxyacetic acid.?2018,Dalian Institute of Chemical Physics,Chinese Academy of Sciences.Published by Elsevier B.V.All rights reserved.

Characteristics and Photocatalytics Activities of Ce-Doped ZnO Nanoparticles

Ce-doped ZnO nanoparticles with various doping concentrations of cerium ion were prepared by the co-precipitation method. All prepared nanoparticles were characterized by electron spin resonance (ESR), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and UV-Vis diffuse reflectance spectroscopy. All nanoparticles show X-ray diffraction pattern that matched with ZnO in its wurzite structure and average grain size was in the range of 13 - 16 nm. UV-Vis measurements indicated a red shift of the photophysical response of ZnO after doping that was exhibited in reflection spectra in the visible region between 300 - 800 nm. In addition, it has been found from electron spin resonance measurements that defects, which are likely to be oxygen vacancy and an electron trapped at cerium site are formed in our Ce-doped ZnO particles. Photocatalytic activities of Ce-doped ZnO were evaluated by irradiating the nanoparticles solution to ultraviolet light by taking methyl orange as organic dye. The experiment demonstrated that the photodegradation increased as doping concentrations increased at first and then decreased when the doping concentra- tion exceeded 9 at%. It is proposed that the photocatalytic activity is strongly dependent on the formation of oxygen vacancy and an electron trapped at cerium site.