Internal electric field boosting visible photocatalytic degradation of antibiotics by flower-like CeO₂/Bi₂S₃ S-scheme heterojunctions

An internal electric field can be formed by constructing a heterojunction to achieve effective separation of photogenerated electrons and holes, which is able to solve the problem of easy compounding of photogenerated carriers in a single semiconductor photocatalyst. This research employs a hydrothermal synthesis technique to develop S-scheme heterojunction photocatalysts composed of cerium oxide and bismuth sulfide (CeO₂/Bi₂S₃) and evaluates their efficacy in degrading TC under visible light. The formation of S-scheme heterojunctions was confirmed by X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations showing that electrons migrate, and the internal electric field of the S-scheme heterojunctions achieves the separation of the electron-hole pairs, retaining the redox capacity of useful electrons and holes, which is responsible for the enhancement of the photocatalytic activity. The synthesized CeO₂/Bi₂S₃-2 photocatalysts demonstrated a TC degradation rate of 82.43% after a duration of 120 minutes under visible light irradiation. The rate constant of this performance was two times greater than that of CeO₂ alone and 2.75 times greater than that of Bi₂S₃. In addition, free radical trapping experiments and electron paramagnetic resonance results confirmed that ·O₂ ^- and h⁺ are active substances in the photocatalytic reaction process. Liquid chromatography-mass spectrometry (LC-MS) detected possible intermediates and suggested degradation pathways. This study has significant implications for the future development and enhancement of S-scheme heterojunction photocatalysts, contributing to advancements in photocatalytic materials.