Facile Synthesis of Rice Husk Derived SiO2/g-C3N4 Heterostructures for Enhanced Photocatalytic Degradation of Dyes and Antibiotics Under Visible Light

Abstract

In this work, SiO₂/g-C₃N₄ photocatalyst was prepared using rice-husk-derived silica (SiO₂-RH) and urea-derived g-C₃N₄ by a simple calcination method. The SiO₂/g-C₃N₄ composites were prepared with different g-C₃N₄ loadings (20, 25, and 30 wt%) and analyzed for visible-light degradation of methylene blue (MB) and ciprofloxacin (CIP). X-ray diffraction (XRD) results confirmed the presence of amorphous SiO₂ and the intact g-C₃N₄ structure. UV–vis DRS results showed that the band gap decreased from 3.25 eV (g-C₃N₄) to 2.81 XRD results confirmed predominantly amorphous rice-husk-derived SiO₂ together with the characteristic g-C₃N₄ structure. eV (SiO₂-CN25). Photoluminescence (PL) results, photocurrent (7.6 µA cm⁻²) and EIS (R_ct = 28.7 Ω cm²) confirmed better charge transfer and lower electron–hole recombination. Textural analysis showed a large surface area of 168.3 m² g⁻¹ and mesopores (8–10 nm) for SiO₂-CN25. Under visible light (λ > 420 nm), SiO₂-CN25 degraded 94% of MB and 89% of CIP in 90 min, with rate constants of 0.031 and 0.027 min⁻¹. The optimized SiO₂-CN25 also showed good stability, retaining 90% of its initial photocatalytic activity after five consecutive reuse cycle 2.8s. The biomass-derived, metal-free SiO₂-CN25 shows high efficiency, stability and eco-friendliness for visible-light wastewater treatment.