Efficient photocatalytic dehydrogenation and synergistic selective oxidation of benzyl alcohol to benzaldehyde for Zn_0.5Cd_0.5S co-modified with MoS₂ nanoflowers and g-C₃N₄ nanosheets

Zn_0.5Cd_0.5S solid solution co-modified by MoS₂ nanoflowers and g-C₃N₄ nanosheets (C₃N₄/MoS₂/Zn_0.5Cd_0.5S) was synthesized with highly efficient photocatalytic dehydrogenation and synergistic selective oxidation of benzyl alcohol (BA) to benzaldehyde (BAD). The photocatalytic dehydrogenation rate and BAD yield are 1.7 mmol·g⁻¹·h⁻¹ and 35.8% for C₃N₄/MoS₂/Zn_0.5Cd_0.5S, and selective oxidation to BAD is almost 100%. Reaction selectivity was explored by detecting all the substances of the solution after reaction for Zn_0.5Cd_0.5S and C₃N₄/Zn_0.5Cd_0.5S using gas chromatography-mass spectrometry (GCMS), and analysis results indicated that BA was converted to other substances because of the insufficient hole oxidation capacity of the samples. The mechanism for highly efficient photocatalytic dehydrogenation and synergistic selective oxidation of BA to BAD was systematically investigated by electron paramagnetic resonance (EPR) and first-principle density-functional theory calculations. The EPR spectra of the phenyl-N-tert-butyl-nitrone (PBN)-carbon centered radical indicated that ·C induced by photo-generated holes are the key intermediate of the photocatalytic dehydrogenation of BA. The loading of flower-like MoS₂ accelerates charge transport and enhances the hole oxidation ability of Zn_0.5Cd_0.5S, and the introduction of g-C₃N₄ has a negative valence band potential that can collect photogenerated holes of Zn_0.5Cd_0.5S, thereby inhibiting photocorrosion. Therefore, the photocatalytic dehydrogenation and synergistic selection of BA to BAD for the C₃N₄/MoS₂/Zn_0.5Cd_0.5S ternary heterostructure were greatly improved. The research work would provide a feasible, sustainable, economical, and potential technique for the highly efficient dehydrogenation and synergistic selective oxidation of BA based on photocatalysis that excludes the usage of noble metals and sacrificial reagents.