Dual Charge Transfer Mechanisms in Intimately Bonded S-scheme Heterojunction Photocatalyst with Expeditious Activity toward Environmental Remediation

Fabrication of a photocatalyst with the desired characteristics of high charge isolation and expeditious photocatalytic performance is crucial in photocatalysis. Constructing an interfacial chemically bonded S-scheme heterojunction is an effective path to the realization of high interfacial charge transfer and performance. Herein, Mg-Bi₂O₃/dark gray g-C₃N₄ (MBOdCN) S-scheme heterojunction with Bi-N bond bridges is successfully constructed using an in situ calcination strategy for oxytetracycline (OTC) degradation. The MBOdCN (1:5) displays outstanding performance with efficiency and rate constant of 99.56% and 0.0235 min⁻¹, respectively. The synergy of n-π* transition, Mg defects, and Bi–N bond bridges in the MBOdCN enhances the performance of the S-scheme heterojunction. X-ray photoelectron spectroscopy (XPS) analysis, work function measurements, and density functional theory (DFT) reveal the formation of MBOdCN S-scheme heterojunction. In this system, trapping experiments and electron-spin resonance (ESR) spectroscopy confirm the predominance of ^•O₂⁻ > h⁺ > ^•OH during OTC degradation. The degradation pathways and byproducts are investigated with LC-MS and the toxicity study is undertaken on the OTC degradation byproducts and photocatalytic materials. This work provides a holistic understanding of the novel S-scheme heterojunction by introducing interfacial chemical bond bridges and defects as dual charge transfer channels.