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

Abstract

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 μmol g⁻¹ h⁻¹) was twice that of TiO₂; moreover, a large amount of CH₃OH was produced (at a rate of 9.1 μmol g⁻¹ h⁻¹). The significantly improved photocatalytic activity was not only due to the increased specific surface area (110 m² 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.