Grinding-assisted calcination synthesis of S-scheme In2O3/S-doped g-C3N4 heterojunctions for enhanced photocatalytic antibiotic removal

Abstract

The ubiquitous accumulation of antibiotic residues in aquatic environments poses a severe threat, necessitating efficient and sustainable remediation technologies like photocatalytic oxidation. To overcome the rapid charge recombination of single-component photocatalysts, we constructed a novel S-scheme heterojunction comprising In2O3 nanoparticles anchored on S-doped g-C3N4 (In2O3/SCN) via a facile grinding-assisted calcination strategy. This specific architecture was selected because the perfectly matched energy band alignment between the highly reductive S-doped g-C3N4 and highly oxidative In2O3 provides a strong thermodynamic driving force for spatial charge separation while preserving their maximum redox potentials. Under visible light irradiation, the optimized In2O3/SCN composite exhibited broad-spectrum photocatalytic activity, achieving outstanding degradation efficiencies of 92% for tetracycline (TC) and 75% for nitrofurantoin (NTF) within 120 min, alongside excellent operational stability over five consecutive cycles. The experimental characterizations and density functional theory (DFT) calculations revealed that the synergistic effect of S-doping and the S-scheme heterojunction significantly facilitated the rapid spatial separation of photogenerated electron-hole pairs. Driven by a strong built-in internal electric field, the S-scheme charge transfer pathway successfully preserved the maximized redox potentials of the carriers. Furthermore, free radical trapping and electron spin resonance (ESR) analyses confirmed that •OH acted as the dominant reactive species in the degradation process. Finally, the deep mineralization pathways of TC and NTF were systematically elucidated via LC-MS analysis. This work provides deep insights into the rational design of highly efficient S-scheme heterojunctions for complex pharmaceutical wastewater remediation.