Rice husk biochar-boosted BiOCl nanoplates: a sunlight-responsive route to wastewater detoxification and pathway insights for methylene blue degradation

Abstract

Heterojunction photocatalysts have attracted significant attention due to their ability to enhance pollutant degradation efficiency. In this study, bismuth oxychloride/rice husk biochar (BO/RB) heterojunction photocatalysts with different mass ratios (1 : 1, 1 : 3, and 3 : 1) were successfully synthesized via an in situ approach and comprehensively characterized using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible diffuse reflectance spectroscopy (UV–DRS), photoluminescence (PL) spectroscopy, and Brunauer–Emmett–Teller (BET) surface area analysis, confirming their structural integrity and high levels of porosity. The incorporation of RB onto BO broadened solar light absorption, enhanced charge carrier separation, and increased the surface area, resulting in improved photocatalytic degradation of methylene blue (MB). The degradation process was optimized by varying catalyst dosage, pollutant concentration, light source, pH, and contact time. Under optimized conditions, BR13 achieved 99% removal of 10 ppm MB within 100 min at pH ≥ 7 under sunlight, following pseudo-first-order kinetics with a rate constant of 0.01761 min⁻¹, exceeding that of commercial TiO₂-P25 (0.00922 min⁻¹). Reusability studies demonstrated good stability, retaining 92.3% degradation efficiency after five cycles. Radical scavenging experiments identified holes (h⁺) and hydroxyl radicals (˙OH) as the dominant reactive species. Additionally, BR13 exhibited effective mineralization, achieving 62% COD and 55% TOC reduction for MB. Due to its high photocatalytic efficiency, stability, and simple synthesis, the BO/RB heterojunction shows strong potential for large-scale wastewater treatment and mitigation of persistent organic pollutants.