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

Abstract

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.