Enhancement Of Photo(Electro) Catalytic Activity Of Tungsten Trioxide And Titania

Semiconductor heterogeneous photocatalysis has been widely studied and recognized as a highly efficient and promising advanced oxidization technology for the degradation of environmental contaminants for several decades.It has tremendous promising application in environmental protection due to its advantages of(â…°) destroying pollutant at normal temperature and pressure by utilizing photocatalyst, light,and air alone,and(â…±)in the long run,its potentially utilizing the inexhaustible sun energy.TiO₂ is the most popular photocatalyst because of its high reactivity, chemical stability under ultraviolet light,nontoxicity,and low cost.However,two major problems should be solved before the practical application of this technology on a large scale:one is the too narrow light absorption range of TiO₂ to utilize most of the sun energy;another is the low efficiency of the photocatalytic reaction(usually＜1%). Therefore,concerning the above-mentioned problems,in this thesis we devoted to developing a new photocatalyst with visible light response and improving the efficiency of TiO₂ aqueous photocatalysis for the degradation of pollutants.The photocatalytic mechemism was also investigated in our work.The thesis includes two parts.In part one,the Zn-doped WO₃ thin film electrode was prepared on indium-tin oxide(ITO)glass.Different preparation conditions,such as concentration of Zn, annealing temperature and coating layers were optimized.The as-prepared electrodes were applied in the degradation of NO₂^- under visible light.Series experimental conditions including applied potential,atmosphere,initial pH,initial nitrite concentration,supporting electrolyte and organic additives were investigated systematically.The results show that both the photocurrent response and the photoelectrocatalytic activity of WO₃ under visible light were enhanced by doping with a suitable amount of Zn.The investigation of mechanism indicated that Zn doped into the WO₃ lattice made the bandgap slightly narrow,which allowed more efficient absorption of visible light and thus more generation of photocarriers.When an anodic potential high enough was applied on the electrode,these photogenerated carriers would be separated efficiently,improving the photoelectrocatalytic degradation performance.The second part is mainly some work devoting to improving the photocatalytic activity of TiO₂,including two sections:Surface-fluorinated TiO₂ nanoporous film electrode was prepared by electrochemical anodization of TiO₂ in HF aqueous solutions formed by direct thermal oxidization of titanium sheet.The photocurrent response of surface-fluorinated TiO₂ was improved so was the incident photon to current efficiency.It was also found in the photocatalytic(open circuit)and photoelectrocatalytic(applied anodic bias) degradation of phenol,methylene blue and reactive brilliant red X3B,the photoactivity of the etched TiO₂ electrodes was also enhanced comparing with that of the unetched one.To account for these enhanced activites,many physicalchemistry characterization methods,such as XRD,Raman,SEM,XPS,UV-Vis diffuse reflectance spectroscopy and photoluminescence spectroscopy,were applied to investigate the crystalline structure,surface morphology and the light absorption property.Electrochemistry and photoelectrochemistry methods were also applied to study the band structure of the etched and unetched TiO₂.The results show that the improvements can be attributed to the enhancement of surface area due to the formation of nanoporous structure on the surface of TiO₂,negative-shift appearing energy band edges and decrease of surface state which usually acts as the recombination centers.The effect of Cl^- concentration and initial pH value on the photoelectrocatalytic degradation of NO₂^- was studied using a thermal oxidation(TO)rutile TiO₂ as the photoanode,and the production rate of active chlorine was also investigate.The photocatalytic activity of TO-TiO₂ was also compared with an anatase TiO₂.The results showed that the rutile TO-TiO₂ has an advantage of the anatase TiO₂ in terms of active chlorine production and the photocatalytic activity of TiO₂ film electrodes was greatly enhanced in the presence of Cl^-.The mechanism study found more active chlorine that had longer lifetime was available to take part in the oxidation of NO₂^-,which should be responsible for the improvement of degradation rate...