Photocatalytic CO2 conversion on highly ordered mesoporous materials: Comparisons of metal oxides and compound semiconductors

In this study, the ordered mesoporous metal oxides (TiO2 and SnO2) and compound semiconductors (ZnS, ZnSe, CdS, and CdSe) are manufactured and they exhibit several micrometers (mu m) of particle size, and high surface area of about 100 m(2)g(-1). Well-developed crystallinities are prepared via simple nano-replication method by using a 3-D bicontinuous cubic Ia3d meso-structured ordered mesoporous silica HIT-6 as a hard-template. The visible-light-driven photocatalytic CO2 conversion into CH4 is carried out in the presence of H2O over various mesoporous materials. Prepared mesoporous materials show different light absorption behaviors and photo catalytic activities for conversion of CO2. The mesoporous compound semiconductors show higher CO yield rates than the mesoporous metal oxides, while mesoporous metal oxides show higher CH4 yield rates than the mesoporous compound semiconductors. Compared to the commercial TiO2 material (P25, Degussa), the mesoporous metal oxides (TiO2, SnO2) show 9 to 10 times higher yields of CH4 and 2 to 3 times higher yields of CO owing to their high surface area. Especially, the mesoporous ZnS shows the highest CH4 yield rate (3.620 mu mol g(cat)(-1)h(-1)) and the mesoporous CdSe shows the highest CO yield rate (5.884 mu mol g(cat)(-1)h(-1)) out of all photocatalysts considered in the present study. Although mesoporous CdS and ZnSe have great visible light absorption properties, they show relatively low CH4 yield rates.