Unravelling the visible light-assisted catalytic prowess of an n–n type In2S3/CeO2 Z-scheme heterojunction towards organic and inorganic water pollution mitigation

Abstract

The exploitation of visible light active photocatalysts for the removal of various pollutants has been given tremendous consideration in water and wastewater treatment. Herein, a novel In₂S₃/CeO₂ n–n type heterojunction photocatalyst was successfully synthesized by a two-step method involving hydrothermal synthesis and subsequent ultrasonic treatment to couple In₂S₃ with CeO₂ (5, 10 and 15 wt%). The as-synthesized samples were characterized extensively using analytical techniques such as XRD, UV-vis-DRS, SEM-EDX, TEM, BET, PL, EIS and XPS to examine the chemical composition, phase structure, morphology and photo-chemical characteristics of the materials. Subsequently, the In₂S₃/CeO₂ nanostructures were employed in the degradation of oxytetracycline (OTC) (10 mg L⁻¹) and reduction of Cr(VI) (50 mg L⁻¹) in aqueous solutions, upon exposure to visible light. Under optimised experimental conditions, the nanocomposite constituting 10 wt% CeO₂ (In₂S₃/10 wt% CeO₂) showed the highest activity, reaching 87.9% OTC degradation and 97.5% Cr(VI) reduction after 60 min and 40 min of visible light irradiation, respectively. The nature and contribution of active species in the photocatalytic process were revealed through radical scavenging studies. Finally, a plausible band structure, charge separation and transfer mechanism were crafted to illustrate the synergy between In₂S₃ and CeO₂ which led to improved degradation kinetics. This work demonstrated a simple route for improving the visible light-mediated activity of In₂S₃ by coupling with CeO₂ and the potential versatility of the composite material for the removal of both organic and inorganic pollutants from water.