In Situ Irradiated X-Ray Photoelectron Spectroscopy Investigation on a Direct Z-Scheme TiO2/CdS Composite Film Photocatalyst

Inspired by nature, artificial photosynthesis through the construction of direct Z-scheme photocatalysts is extensively studied for sustainable solar fuel production due to the effectiveness in enhancing photoconversion efficiency. However, there is still a lack of thorough understanding and direct evidence for the direct Z-scheme charge transfer in these photocatalysts. Herein, a recyclable direct Z-scheme composite film composed of titanium dioxide and cadmium sulfide (TiO2/CdS) is prepared for high-efficiency photocatalytic carbon dioxide (CO2) reduction. In situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) confirms the direct Z-scheme charge-carrier migration pathway in the photocatalytic system. Furthermore, density functional theory simulation identifies the intrinsic cause for the formation of the direct Z-scheme heterojunction between the TiO2 and the CdS. Thanks to the significantly enhanced redox abilities of the charge carriers in the direct Z-scheme system, the photocatalytic CO2 reduction performance of the optimized TiO2/CdS is 3.5, 5.4, and 6.3 times higher than that of CdS, TiO2, and commercial TiO2 (P25), respectively, in terms of methane production. This work is a valuable guideline in preparation of highly efficient recyclable nanocomposite for photoconversion applications.