NiS/Cd0.6 Zn0.4 S Schottky Junction Bifunctional Photocatalyst for Sunlight-Driven Highly Selective Catalytic Oxidation of Vanillyl Alcohol Towards Vanillin Coupled with Hydrogen Evolution Reaction

Abstract

Selective oxidation of biomass-based molecules to high-value chemicals in conjunction with hydrogen evolution reaction (HER) is an innovative photocatalysis strategy. The key challenge is to design bifunctional photocatalysts with suitable band structures, which can achieve highly efficient generation of high-value chemicals and hydrogen. Herein, NiS/Cd_0.6 Zn_0.4 S Schottky junction bifunctional catalysts are constructed for sunlight-driven catalytic vanillyl alcohol (VAL) selective oxidation towards vanillin (VN) coupling HER. At optimal conditions, the 8% NiS/Cd_0.6 Zn_0.4 S photocatalyst achieves high activity of VN production (3.75 mmol g^-1 h^-1 ) and HER (3.84 mmol g^-1 h^-1 ). It also exhibits remarkable VAL conversion (66.9%), VN yield (52.1%), and selectivity (77.8%). The photocatalytic oxidation of VAL proceeds a carbon-centered radical mechanism via the cleavage of α_C-H bond. Experimental results and theoretical calculations show that NiS with metallic properties enhances the electron transfer capability. Importantly, a Ni-S-Cd "electron bridge" formed at the interface of NiS/Cd_0.6 Zn_0.4 S further improves the separation/transfer of electrone/h⁺ pairs and also furnishes HER active sites due to its smaller the |ΔG_H* | value, thereby resulting in a remarkably HER activity. This work sheds new light on the selective catalytic oxidation VAL to VN coupling HER, with a new pathway towards achieving its efficient HER efficiency.

Keywords: NiS/Cd0.6Zn0.4S Schottky junction bifunctional photocatalysts; hydrogen evolution reaction; selective photocatalytic oxidation; vanillyl alcohol.