Softwood biochar-supported Bi2WO6 for photocatalytic degradation of organic contaminant mixture in river water: Role of pyrolysis temperature and surface functionality

The design of efficient biochar-supported photocatalysts for the removal of emerging contaminants requires a fundamental understanding of the influence of biochar properties on photocatalyst structure and performance. This study presents a comprehensive investigation of the effects of biochar feedstock and pyrolysis temperature on the structural, optical, and photocatalytic properties of biochar-supported bismuth tungstate (Bi₂WO₆) composites for the degradation of 1,3-diphenylguanidine (DPG) and other emerging contaminants. Biochar derived from two softwood feedstocks (cedar and a mix of pine and spruce) was pyrolyzed at different temperatures (300 °C, 400 °C, 500 °C, and 600 °C) to serve as a support for Bi₂WO₆. This work reveals the critical impact of biochar surface area, porosity, and redox-active functional groups on the interaction with Bi₂WO₆, which influence the crystal orientation, surface area, redox properties, and the resulting composite photocatalytic behavior. Composites synthesized using biochar pyrolyzed at 400 °C demonstrated optimal performance and a 74-fold enhancement in DPG photocatalytic rate constant compared to bare Bi₂WO₆. The optimal composite was further applied to treat river water spiked with five organic contaminants, achieving 94.36 % removal of the total mixture and a 55.4 % reduction in total organic carbon, confirming its effectiveness in complex matrices. This study highlights the critical role of biochar support properties in enhancing the photocatalytic activity of Bi₂WO₆ and establishes guidelines for the development of sustainable photocatalysts for water treatment applications.