Study On Synthesis And Visible-Light Driven Photodegradation Properties Of WO₃-based Catalysts

With the rapid development of industry and economy,the informal discharge of industrial wastewater has brought serious water pollution to the ecological environment.Phenol and its derivatives are a class of high toxicity organic pollutants.In many industrial processes,such as refining,metallurgy,machinery manufacturing,organic synthesis,will produce a large number of phenol wastewater,if these phenolic wastewater without direct discharge,can cause serious pollution of water and soil.The traditional treatment of phenolic pollutants such as adsorption method,extraction method,are inefficient and often bring secondary pollution and other shortcomings.The photocatalytic oxidation of semiconductor has the advantages of mild reaction,high efficiency and environmental friendliness,and has attracted wide attention in the treatment of phenolic pollutants.As a semiconductor photocatalyst,tungsten trioxide shows better performance in the degradation of phenolic pollutants.However,the active sites of WO₃ photocatalyst is less and the absorption range of visible light is narrow,which affects the photocatalytic activity of WO₃.Considering the above-metioned problems,a micro/nanoscale spherical WO₃ with a large specific surface area was synthesized and the bandgap of WO₃ was reduced by Mo doping to improve its photocatalytic activity.H₂O₂ was used as accelerant with photocatalyst to further improve its degradation performance.The photocatalysr were characterized by X-ray powder diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,Scanning electron microscopy?SEM?,Transmission electron microscopy?TEM?,UV-Vis diffuse reflectance spectroscopy?DRS?,Photoluminescence?PL?and nitrogen sorption-desorption,and the degardation performance and mechanism of photocatalyst were evaluated.Principal results are as follows:In part one,tungsten trioxide photocatalyst were synthesized by solwent thermal method combine calcination treatments,and characterized by XRD,SEM,TEM,DRS and BET.The results of XRD indicate that WO₃ is ? phase.The results of SEM and TEM reveal that the synthesized WO₃ is spherical structure in particle size of 500-1000 nm;the results of DRS show that the synthesized WO₃ band gap is 2.7 eV,which can absorb sunlight with less than 470 nm in the visible region;the test of BET shows that the calculated value of specific surface area is 9.08 m2·g-1,and the pore size is about 1.9 nm.In part two,the low concentration of phenol solution as the target degradation reactant evaluate the degradation performance of WO₃.The effects of tungsten trioxide calcination temperature,photocatalyst concentration,pH value of the reaction system,accelerant H₂O₂ concentration and pollutant concentration on the photodegradation of WO₃ were investigated.The results show that the degradation rate of phenol could reach 94% in 180 min under the following circumstances: the calcination temperature of WO₃ is 600 °C,the initial concentration of phenol is 10 mg/L,and the concentration of H₂O₂ is 1 m L,the pH of the solution is 6.3,the optimum photocatalyst concentration is 0.5 g/L.The L-H model show that WO₃ and H₂O₂ photodegradation of phenol accorded with quasi-first-order kinetics.The cycling stability test show that WO₃ still has better chemical stability after five cycles.In addition,the mechanism of photocatalytic degradation of phenol by WO₃ and H₂O₂ was investigated.The results show that ·OH,h+and O2-· are all active groups of oxidized phenol,the presence of H₂O₂ is favorable for the production of ·OH,thereby enhancing the efficiency of WO₃ photodegradation of phenol.In part three,Mo-doped WO₃ photocatalyst were synthesized by solwent thermal method combine calcination treatments,and characterized by XRD,XPS,SEM,TEM,DRS and PL.The results of XRD indicate that photocatalyst is still ? phase;the shift of peaks in the spectra of XRD and XPS indicates that molybdenum ion are doped into the lattice of the WO₃;The results of SEM and TEM reveal that the synthesized Mo-doped WO₃ is spherical structure in particle size of 600-1000 nm;the results of DRS show that Mo-doping leads to decrease the the bandgap of WO₃,and its absorption range of visible light is broadened;the peak at 440-490 nm is weakened in the PL spectrum indicates that Mo-doping leads to increase the photo-generated electron and hole separation rate of WO₃ photocatalyst.In part four,the phenol and p-chlorophenol solution as the target degradation reactant evaluate the degradation performance of Mo-doped WO₃.The effect of the proportion of Mo dopant on the photodegradation of WO₃ was inverstigated.The results show that the optimal photocatalyst is 0.94 wt% Mo-doped WO₃,and the degradation rate of phenol reach 95% after 120 min,the degradation rate of p-chlorophenol reach 96% after 90 min.The effects of the concentration of photocatalyst and the amount of H₂O₂ on the degradation of phenol were investigated.The optimum photocatalytic concentration is 0.5 g/L and the optimum amount of H₂O₂ is 1 mL.The L-H model show that Mo-doped WO₃ and H₂O₂ photodegradation of phenol and p-chlorophenol are accordance with quasi-first-order kinetics.The cycling stability test show that Mo-doped WO₃ still have better chemical stability after five cycles.In addition,the mechanism of photocatalytic degradation of p-chlorophenol by Mo-doped WO₃ was investigated.The results show that ·OH,h+and O2-· have played an important role in photodegradation of p-chlorophenol.