Pivotal role of surface and bulk Gd species in WO3 to promote Type-II charge carrier transfer pathways in Gd-WO3/g-C3N4 heterojunction photocatalyst

Tailoring the surface-bulk structure of narrow gap semiconductors has been the prominent strategy to promote both light absorption properties and charge carrier separation. In this context, monoclinic-WO3 is modified with gadolinium (GWO) through a wet chemical approach and integrated with 2D g-C3N4 (GCN) via simple annealing step to form unique heterostructure (GWOGCN). The X-ray diffraction revealed that Gd3+ ion substitutes the bulk structure of WO3 and distributes over the surface. The UV-visible absorption spectra confirmed significant improvement in the light absorption properties of heterostructures compared to pure phase materials. The results from the photoluminescence and electrochemical impedance spectroscopy collectively suggested the low degree of charge transfer resistance with improved carrier separation in the GWOGCN heterojunction. The pivotal role of Gd species and the construction of Type-II heterojunction between GWO and GCN was ascribed to the superior activity of GWOGCN. The half-filled electronic configuration of Gd3+ dopant accelerates the shallow trapping of charge carriers, while the surface Gd species transferred the charge carriers to the adsorbed species. The beneficial role of Gd and formation of Type-II heterostructure was also evidenced from the density functional theory calculations. The findings of the present research open an avenue for the fabrication of heterostructures comprised with narrow-gap semiconductors through a facile approach.