The Influence Of Crystal Structure And Cocatalyst On TiO₂Photolysis Of Water Hydrogen Production

Since the21st century, how to alleviate the contradiction between economic growthand energy crisis has become a problem which need to be solved immediately.Fujishima and Honda successfully decomposed water to generate hydrogen using theelectrochemical method for the first time in1972, the preparation of cleanenergy-hydrogen with solar energy has received much attention by governments andscientists.TiO₂is non-toxic and cheap with good photocatalytic activity and chemicalstability, so it has excellent application prospect in the fields of photocatalytichydrogen production from water, sewage treatment, solar cells etc. In recent years,TiO₂has been paid more and more attention as a kind of photocatalytic material.The three existence forms of TiO₂crystal are brookite, anatase and rutile in nature.Brookite is rarely used as a photocatalyst because of the instability of brookite. In thispaper, TiCl₄was used as precursor to prepare the single crystal structure of anataseand rutile under low temperature conditions, respectively. The synthetic samples werecharacterized and compared with different commercial TiO₂（P25、ST-21、ST-31） tomeasure the property of photocatalytic hydrogen production from pure water and theproperty of hydrogen production and oxygen production while methanol and silvernitrate were used as sacrificial agents. The experimental results showed thatphotocatalytic activity of TiO₂with different crystal form mainly depend on surfaceproperties and size of crystal particle and content of sacrifice agent etc. In the TiO₂with mixed crystal structure, the synergy of rutile and anatase made the electron flowfrom the conduction band of rutile type TiO₂to the one of anatase type TiO₂, thus thelight quantum yield was improved. Therefore, hydrogen production efficiency of TiO₂with mixed crystal structure is better than TiO₂with single crystal.In the process of photocatalytic hydrogen production from water, composite ofphotoproduction electrons and holes is the important factors that affect thephotocatalytic performance. Commonly used solution is loading a small amount ofnoble metals on the catalyst surface as cocatalyst. But the cost is very high, thereforeseeking of cheaper non-noble metal catalyst promoter has become one of researchhotspots in the field of hydrogen production from water splitting. In the present paper, photocatalysts CuS/P25for hydrogen production were synthesized by hydrothermalmethod at high temperature and characterized by XRD, TEM, SEM and EDX,indicating that CuS does exist in the surface of P25. The photocatalysts with beforeand after reaction were characterized by XPS analysis, indicating that CuS/P25hadgood light stability. And photoluminescence test prove that CuS as a cocatalyst caneffectively inhibit recombination of photoproduction electrons and holes on thesurface the catalyst. The amount of the evolved H2for1wt%CuS/P25has noobvious degradation occurs after the10h of photocatalysis test, indicating a potentialstable photocatalytic property. Among the photocatalysts with various compositions,the one with1wt%CuS/P25showed the maximum photocatalytic activity for watersplitting, the amounts of the produced hydrogen were about570μmol·h-1, which hasexceeded32times of P25. At the same time, we used CuS and ZnS as dual co-catalystto improve the anatase efficiency of photocatalytic hydrogen production. Thephotocatalytic experiments indicated dual co-catalyst can be efficiently separatedphoto-generated electron-hole pairs. And5wt%CuS-ZnS/TiO₂have the highestphotocatalytic efficiency.