Photodegradation of diclofenac in aqueous media via a HO˙ radical pathway using CeO2/g-C3N4 heterojunction under visible light: experimental and computational insights

Abstract

Diclofenac (DCF), a widely prescribed nonsteroidal anti-inflammatory drug (NSAID), is frequently detected in aquatic environments due to its extensive usage and poor removal by conventional wastewater treatment technologies. Among various remediation strategies, photocatalysis has emerged as a cost-effective and sustainable approach for the degradation of such persistent pharmaceutical pollutants. In this study, a CeO₂/g-C₃N₄ heterojunction photocatalyst was synthesized and optimized for the visible-light-driven photodegradation of DCF in aqueous media. Under optimized conditions (catalyst dosage: 0.5 g L⁻¹, initial pH: 6.8, light source: 200 W Xe lamp with λ > 420 nm cutoff filter), the composite achieved 92.6% DCF removal and 75% TOC removal after 180 minutes, demonstrating both efficient degradation and substantial mineralization. The improved photocatalytic activity can be attributed to the effective separation of photogenerated charge carriers, made possible by forming a type-II heterojunction and the strong visible-light absorption capacity of the composite. Radical scavenging experiments confirmed that hydroxyl radicals (˙OH) play a dominant role in the degradation mechanism, while complementary DFT-based computational analysis provided further support by revealing a high rate constant (k = 1.56 × 10¹⁰ M⁻¹ s⁻¹) for the HO˙–DCF reaction. The structural and optical properties of the photocatalyst were thoroughly characterized using XRD, SEM-EDX, UV-Vis DRS, and FT-IR, confirming the successful formation of the CeO₂/g-C₃N₄ heterostructure. These results highlight the practical potential of CeO₂/g-C₃N₄ for wastewater treatment and solar-driven environmental remediation, providing guidance for designing advanced photocatalytic systems targeting recalcitrant pollutants.