Walnut shell biochar supported TiO₂–g-C₃N₄ heterojunction photocatalyst for solar photocatalytic degradation of congo red

Biochar has multiple applications, one of which is to act as a supporting material for catalysts in various treatment processes. Solar-light-driven photocatalysis is one of the efficient treatment methods for textile industry wastewaters, typically containing recalcitrant organic compounds such as dyes. It offers a convenient, simple, cost-effective and efficient method of radical generation for pollutant degradation using solar energy. The present study investigates the application of walnut shell biochar (WSB) to immobilize the solar light-responsive TiO₂–g-C₃N₄ heterojunction photocatalyst for congo red (CR) dye degradation. Different facile and modified methods for the production of the heterojunction photocatalysts such as the sol-gel method (with and without some modifications), ultrasonication and single-step calcination methods. These samples were then characterized for surface morphology, crystallinity, elemental composition and photoactivity. About 60% degradation efficiency could be achieved for the CR solution with an initial concentration of 10 mg/L and a catalyst dosage of 1 g/L at the end of 3 h irradiation. It was observed that photocatalysis proved to be a major removal mechanism than adsorption by biochar, but the WSB assisted in the easy separation of the photocatalyst from the dye solution after the treatment. The study concluded that the photocatalysts synthesized using facile methods can be effectively employed for CR degradation under solar light irradiation.