Surface defect-engineered CeO2−x by ultrasound treatment for superior photocatalytic H2 production and water treatment

Abstract

Semiconductor photocatalysts with surface defects display incredible light absorption bandwidth and these defects function as highly active sites for oxidation processes by interacting with the surface band structure. Accordingly, engineering the photocatalyst with surface oxygen vacancies will enhance the semiconductor nanostructure's photocatalytic efficiency. Herein, a CeO_2−x nanostructure is designed under the influence of low-frequency ultrasonic waves to create surface oxygen vacancies. This approach enhances the photocatalytic efficiency compared to many heterostructures while keeping the intrinsic crystal structure intact. Ultrasonic waves induce the acoustic cavitation effect leading to the dissemination of active elements on the surface, which results in vacancy formation in conjunction with larger surface area and smaller particle size. The structural analysis of CeO_2−x revealed higher crystallinity, as well as morphological optimization and the presence of oxygen vacancies is verified through Raman, X-ray photoelectron spectroscopy, temperature-programmed reduction, photoluminescence, and electron spin resonance analyses. Oxygen vacancies accelerate the redox cycle between Ce⁴⁺ and Ce³⁺ by prolonging photogenerated charge recombination. The ultrasound-treated pristine CeO₂ sample achieved excellent hydrogen production showing a quantum efficiency of 1.125% and efficient organic degradation. Our promising findings demonstrated that ultrasonic treatment causes the formation of surface oxygen vacancies and improves photocatalytic hydrogen evolution and pollution degradation.