Multi Polyoxometalate / TiO <sub> 2 </ Sub> (the WO <sub> 3 </ Sub>) Composite Catalyst The Water Photolysis Catalytic Performance Study

Design and synthesis of high efficient photocatalyst is significant for solar hydrogen.This research focuses on preparation and characterization of polyoxometallate supported TiO₂ or WO₃ photocatysts for water splitting.Some innovative results are as follows:Polyoxometallate supported catalysts such as H₄SiW₁₂O₄₀/TiO₂,H₄PW₁₂O₄₀/TiO₂,with a high activity under ultraviolet radiation were prepared by sol-gel technology and impregnation methods.Samples were characterized by XRD,EDS,FT-IR,Raman and UV-DRS.Oxygen production rate and reaction mechanism of POM/TiO₂ composite catalysts were investigated.The results indicate that original structure of POM was retained and POM/TiO₂ showed a strong capacity in absorbing ultraviolet.Moreover,as titanium dioxide was in anatase phase,the calcination temperature and time was 250℃and 3h respectively,the mass ratio of TiO₂ to POM was 1:10,the photocatalytic activity reached the top, the fastest oxygen production rate of H₄SiW₁₂O₄₀/TiO₂ was 269.94μmol·l^-1·h^-1,which was 1.4 times to that of H₄SiW₁₂O₄₀,and 4.5 times TiO₂,which showed synergetic effect existed between POM and TiO₂.Two kinds of POM/WO₃ composite catalysts,H₄SiW₁₂O₄₀/WO₃ and H₄PW₁₂O₄₀/WO₃ were prepared by solid-state sintering method and impregnation.XRD,FT-IR,Raman,UV-DRS were applied to characterize their structure and their photocatalytic performance in oxygen production for water splitting under ultraviolet.The result showed that catalysts were in nano size.For POM/WO₃,original structure of POM didn't change significantly.Because of the physical interaction between WO₃ and POM,IR spectra peak intensity of POM/WO₃ changed. Calcination time,temperature,mass ratio(w(WO₃):w(POM))and concentration of Fe³⁺would affect performance of catalysts.As concentration of electron acceptors was 5g/L,and when the ratio(w (WO₃):w(H₄SiW₁₂O₄₀))was 1:10,calcination time and temperature was 3h and 400℃respectively,H₄SiW₁₂O₄₀/WO₃ composite catalyst exhibited the highest photocatalytic activity,and oxygen production rate was 143.13μmol·l^-1·h^-1,however,this value was still lower than that of H₄SiW₁₂O₄₀;when concentration of Fe³⁺was 5g/L,mass ratio(w(WO₃) /w(H₄PW₁₂O₄₀))was 1:5,calcined for 3h under 400℃,the catalyst showed the best performance and oxygen production rate was 114.50μmol·l^-1·h^-1,slightly higher than that of H₄PW₁₂O₄₀.