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

Abstract In this study, the ordered mesoporous metal oxides (TiO 2 and SnO 2 ) and compound semiconductors (ZnS, ZnSe, CdS, and CdSe) are manufactured and they exhibit several micrometers (μm) 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 Ia 3 d meso-structured ordered mesoporous silica KIT-6 as a hard-template. The visible-light-driven photocatalytic CO 2 conversion into CH 4 is carried out in the presence of H 2 O over various mesoporous materials. Prepared mesoporous materials show different light absorption behaviors and photocatalytic activities for conversion of CO 2 . The mesoporous compound semiconductors show higher CO yield rates than the mesoporous metal oxides, while mesoporous metal oxides show higher CH 4 yield rates than the mesoporous compound semiconductors. Compared to the commercial TiO 2 material (P25, Degussa), the mesoporous metal oxides (TiO 2 , SnO 2 ) show 9 to 10 times higher yields of CH 4 and 2 to 3 times higher yields of CO owing to their high surface area. Especially, the mesoporous ZnS shows the highest CH 4 yield rate (3.620 μmol g cat −1 h −1 ) and the mesoporous CdSe shows the highest CO yield rate (5.884 μmol 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 CH 4 yield rates.