Hybrid carbon@TiO2 hollow spheres with enhanced photocatalytic CO2 reduction activity

Photocatalytic conversion of carbon dioxide (CO2) into solar fuels is an attractive strategy for solving the increasing energy crisis and greenhouse effect. This work reports the synthesis of hybrid carbon@TiO2 hollow spheres by a facile and green method using a carbon nanosphere template. The carbon content of the carbon@TiO2 composites was adjusted by changing the duration of the final calcination step, and was shown to significantly affect the physicochemical properties and photocatalytic activity of the composites. The optimized carbon@TiO2 composites exhibited enhanced photocatalytic activity for CO2 reduction compared with commercial TiO2 (P25): the photocatalytic CH4 production rate (4.2 mu mol g(-1) h(-1)) was twice that of TiO2; moreover, a large amount of CH3OH was produced (at a rate of 9.1 mmol g(-1) h(-1)). The significantly improved photocatalytic activity was not only due to the increased specific surface area (110 m(2) g(-1)) and CO2 uptake (0.64 mmol g(-1)), but also due to a local photothermal effect around the photocatalyst caused by the carbon. More importantly, UV-vis diffuse reflectance spectra (DRS) showed a remarkable enhancement of light absorption owing to the incorporation of the visible-light-active carbon core with the UV light-responsive TiO2 shell for increased solar energy utilization. Furthermore, electrochemical impedance spectra (EIS) revealed that the carbon content can influence the charge transfer efficiency of the carbon@TiO2 composites. This study can bring new insights into designing carbon@semiconductor nanostructures for applications such as solar energy conversion and storage.