A novel Cs₂O–Bi₂O₃–TiO₂–ZnO heterostructure with direct Z-Scheme for efficient photocatalytic water splitting

Efficient production of hydrogen through photocatalytic water splitting requires innovative catalyst design. One of the potential ways to enhance the photocatalyst's efficiency is to prepare metal oxide heterostructures. Herein, we report fabrication of a novel heterostructure consisting of oxides of cesium, bismuth, titanium and zinc (Cs₂O–Bi₂O₃–TiO₂–ZnO) by a simple solution combustion method. Diffusion pathway of charge carriers in the as-synthesized Cs₂O–Bi₂O₃–TiO₂–ZnO is investigated by high resolution Valence Band X-Ray Photoelectron Spectroscopy (VB-XPS) and electron spin resonance studies. On the basis of analytical findings and redox potential values of each photocatalytic component, a plausible mechanism is proposed showing the formation and diffusion of charge carrier. The results suggest that the charge carrier migration follows the heterojunction approach among TiO₂, Bi₂O₃, and ZnO and the Z-scheme approach between each of them and Cs₂O. The performance of the as-obtained catalytic system is investigated by quantifying the photocatalytic formation of oxygen and hydrogen gases, as well as photoelectrochemical water oxidation under simulated sunlight irradiation. In addition, the apparent quantum efficiency is estimated as high as 1.56% at 420 nm. The high apparent quantum efficiency is primarily ascribed to the synergetic effect between Z-scheme and heterojunction operative in the as-prepared heterostructure.