Boosting photocatalytic dehydrogenation and simultaneous selective oxidation of benzyl alcohol to benzaldehyde over flower-like MoS₂ modified Zn_0.5Cd_0.5S solid solution

A series of MoS₂/Zn_0.5Cd_0.5S with varying concentrations of flower-like MoS₂ is prepared based on a simple and practical method with highly efficient photocatalytic dehydrogenation and simultaneous selective oxidation of benzyl alcohol (BA) to benzaldehyde (BAD). A comparative study between the composites and their two components (pristine MoS₂ and Zn_0.5Cd_0.5S) is carried out for various structural, optical, electrical, and photocatalytic characterization. The studies reveal that the size of Zn_0.5Cd_0.5S nanoparticles is in the order of 3∼5 nm and is distributed uniformly over the surface of the flower-like 350 nm sized MoS₂. The optical research conducted using UV–vis diffuse reflectance spectroscopy reflecting an excellent photoresponse by the MoS₂/Zn_0.5Cd_0.5S. The photoelectrochemical tests showed that the adding of proper ratio of flower-like MoS₂ (6%) results in an efficient separation and migration of photogenerated carriers for pristine Zn_0.5Cd_0.5S nanoparticles. The photocatalytic dehydrogenation rate of BA for the 6%-MoS₂/Zn_0.5Cd_0.5S is the highest at 3.03 mmol g⁻¹ h⁻¹, meanwhile the yield of BAD and the selective conversion of BA to BAD are 49.3% and 100%, respectively. The essential stages of the photocatalytic dehydrogenation of BA are ·C caused by the photo-generated holes, according to the EPR spectra of the PBN-carbon centered radical (PBN–C). Besides, the mechanism for improved photocatalytic dehydrogenation and synergistic selective oxidation of BA to BAD with flower-like MoS₂ modified Zn_0.5Cd_0.5S nanoparticles was systematically studied through gas chromatography-mass spectrometry analysis and first principle density functional theory calculations. The highly efficient dehydrogenation and synergistic selective oxidation of BA to BAD for MoS₂/Zn_0.5Cd_0.5S are mainly attributed to the introduction of MoS₂ nanoflowers that can provide abundant active sites, and formed MoS₂/Zn_0.5Cd_0.5S heterostructures could further promote the separation of photogenerated electron-hole pairs. Moreover, the valance band position of the 6%-MoS₂/Zn_0.5Cd_0.5S is more positive, so the hole at the VB position has the stronger ability to oxidize BA. This study provides a feasible method for efficiently photocatalytic dehydrogenation synergism selective oxidation of organic substrates into valuable products.