Size-dependent selectivity and activity of CO2 photoreduction over black nano-titanias grown on dendritic porous silica particles

Abstract

Titania (TiO2) materials show great promising for photocatalytic CO2 reduction into solar fuels. However, the CO2 conversion efficiency of most TiO2-based photocatalysts is still low up to now, which mainly results from their low accessible active surface areas and weak light-absorption ability. Herein, we employed dendritic porous silica nanospheres (DPSNs) with high accessible internal surface as carriers to successfully fabricate a series of efficient and robust DPSNs@X% TiO2-x (X%: weight ratio of TiO2/DPSNs) composite photocatalysts with tunable sizes of black TiO2-x NPs. For CO2 photocatalytic selectivety and activity, only CO was generated for 1–3 nm of small TiO2-x NPs on DPSNs@X% TiO2-x (X% ≤ 20%), while both CO and CH4 were produced for 3–12 nm of larger TiO2-x NPs on DPSNs@X% TiO2-x (X% ≥ 40%). Noteworthily, DPSNs@80% TiO2-x showed ultrahigh CH4 production rate of 124.3 μmol g-TiO2-x−1 h−1, moderate CO production rate of 14.7 μmol g-TiO2-x−1 h−1 and high photocatalytic stability. The excellent photocatalytic performance should be attributed to be well-dispersed distribution, appropriate particle sizes, and suitable reduction degree of TiO2-x NPs on the pore surface of DPSNs@80% TiO2-x with high accessible specific surface area (208 m2 g−1). Furthermore, these characteristics lead to higher CO2 adsorption capacity, much lower recombination rate of photogenerated electrons and holes, and enhanced carrier transfer and separation in black TiO2-x, thus demonstrating dramatically high CO2 photoreduction activity. This study may open new perspectives for the design of the supported photocatalysts, in which the morphologies and structures of the carriers are the key parameters.