Optimal construction of WO3·H2O/Pd/CdS ternary Z-scheme photocatalyst with remarkably enhanced performance for oxidative coupling of benzylamines

In this work, an all-solid-state Z-scheme photocatalyst of WO3·H2O/Pd/CdS ternary heterostructures was constructed by introducing a small amount of Pd into the optimized WO3·H2O/CdS binary system, where Pd nanoparticles (NPs) were sandwiched between WO3·H2O nanosheets and CdS NPs. The WO3·H2O/Pd/CdS ternary heterostructures exhibited remarkably enhanced photocatalysis towards the oxidative coupling of benzylamines to imines, compared with the other photocatalysts of WO3·H2O, CdS, WO3·H2O/CdS, WO3·H2O/Pd, and WO3·H2O/CdS/Pd. The wavelength-dependent photocatalysis of WO3·H2O/Pd/CdS is in good agreement with its light-harvesting intensity at the corresponding wavelengths. The photoelectrochemical results reflected the enhanced charge carrier separation in WO3·H2O/Pd/CdS, and the photocatalytic H2 evolution confirmed the highly efficient Z-scheme charge transfer in this ternary photocatalyst. Therefore, the WO3·H2O/Pd/CdS ternary heterostructures possess distinct advantages of extended light harvesting region, spatial separation of electron and holes, and elevated redox power, which synergistically contribute to the superior photocatalysis. The Pd NPs sandwiched between WO3·H2O and CdS acted as not only an electron mediator to facilitate the interfacial charge separation but also a cocatalyst to accelerate the selective oxidation of benzylamine. This work demonstrates a rational design of highly efficient Z-scheme photocatalysts and presents some revelations about the photocatalytic mechanism for selective organic transformations.