Photocatalytic CO2 reduction over SrTiO3: Correlation between surface structure and activity.

Perovskite oxide SrTiO 3 is a promising semiconductor photocatalyst for CO 2 reduction, which has two possible chemical surfaces—TiO 2 -terminated and SrO-terminated surfaces. Up to now, the effect of chemical surface and its modification on CO 2 adsorption, activation and sequential photocatalytic reduction is not established. In the work, SrTiO 3 , surface-Ti-rich SrTiO 3 and Sr(OH) 2 -decorated SrTiO 3 were prepared and their structural, surface, and optical properties and photocatalytic activity were explored. It is found that the absorption edge of surface-Ti-rich SrTiO 3 shifted toward visible-light region as compared with that of the other two photocatalysts, which is attributed to the decreased Ti 3d ground-state level at the surface. Bicarbonate- (HCO 3 − ) and bidentate carbonate-like (b-CO 3 = ) species are the main species for CO 2 adsorption on the surface-Ti-rich SrTiO 3 , whereas, besides HCO 3 − and b-CO 3 = , plenty of monodentate carbonate-like species (m-CO 3 = ) that has relatively low reactivity is present on the SrTiO 3 and Sr(OH) 2 -decorated photocatalysts. As a result, the surface-Ti-rich SrTiO 3 exhibits the highest activity for CO 2 reduction. Furthermore, although Sr(OH) 2 -decoration and SrO-terminated surfaces facilitate CO 2 fixing, the produced surface species are attached to the weakly active Sr ions, giving rise to the lower reactivity. The present work might supply a guide for designing highly active perovskite–type semiconductors for photocatalysis. [ABSTRACT FROM AUTHOR]