Hierarchical TiO2/Ni(OH)2 composite fibers with enhanced photocatalytic CO2 reduction performance

In the past few years, Ni(OH)2 has been found to be an effective cocatalyst for photocatalytic hydrogen evolution. Herein, we report that it can also be used to enhance the photoreduction of CO2 into chemical fuels. Vertically aligned Ni(OH)2 nanosheets are deposited onto electrospinning TiO2 nanofibers via simple wet-chemical precipitation to manufacture TiO2/Ni(OH)2 hybrid photocatalysts. The TiO2 nanofibers can direct the ordered growth of Ni(OH)2 nanosheets, which have a thickness of 20 nm and uniformly cover the surface of the TiO2 substrate. The TiO2/Ni(OH)2 hierarchical composite displays remarkably improved photocatalytic CO2 reduction activity compared to that displayed by pristine TiO2 fibers. The bare TiO2 can only produce methane and carbon monoxide (1.13 and 0.76 μmol h−1 g−1, respectively) upon CO2 photoreduction. After loading 0.5 wt% Ni(OH)2, the methane yield increases to 2.20 μmol h−1 g−1, meanwhile the CO yield is unchanged. Interestingly, alcohols (methanol and ethanol) also appear as products, in addition to CH4 and CO, over the TiO2/Ni(OH)2 hybrid, and the maximum yield is reached with 15 wt% Ni(OH)2 loading (0.58 and 0.37 μmol h−1 g−1 for methanol and ethanol, respectively). This can be ascribed to an enhanced charge separation efficiency and higher CO2 capture capacity due to the presence of Ni(OH)2. These results demonstrate that Ni(OH)2 can not only improve the total CO2 conversion efficiency, but can also alter the product selectivity upon photocatalysis. This work opens a new pathway for achieving high-efficiency photocatalytic CO2 reduction with Ni(OH)2 as a cocatalyst.