Rationally designed In–CeO2/g-C3N4 S-scheme heterojunction photocatalyst with tuned redox ability for the photocatalytic degradation of pharmaceutical contaminants

Abstract

Herein, the synthesis of an indium-doped cerium oxide/graphitic carbon nitride (In–CeO₂/g-C₃N₄) S-scheme heterojunction aimed at optimizing photocatalytic degradation under visible light for the remediation of pharmaceutical wastewater is reported. The materials were synthesized via a hydrothermal process, in which pure CeO₂ and In-modified CeO₂ (In–CeO₂) were initially synthesized, followed by the incorporation of g-C₃N₄ to produce the heterojunction. A series of characterization methods, such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), validated the effective synthesis and structural integrity of CeO₂, In–CeO₂, and In–CeO₂/g-C₃N₄. The optical bandgap of the samples was determined, presenting a reduction from 2.97 eV for CeO₂ to 2.69 eV for In–CeO₂/g-C₃N₄, which facilitated better visible-light absorption. Photocurrent and electrochemical impedance spectroscopy (EIS) characterizations indicated enhanced charge separation and reduced recombination in the In–CeO₂/g-C₃N₄ heterojunction. Photocatalytic experiments for the degradation of levofloxacin (LVX) demonstrated that the In–CeO₂/g-C₃N₄ heterojunction achieved 85% degradation, significantly higher than those achieved by In–CeO₂ (63%) and CeO₂ (44%), highlighting the enhanced photocatalytic performance of the heterojunction. The higher photocatalytic activity is attributed to the formation of an S-scheme charge migration channel, enabling efficient charge separation. Results indicate that the In–CeO₂/g-C₃N₄ heterojunction has great potential for water purification applications, particularly in degrading drug contaminants.