Engineering BiSI-based catalysts for optimized sonophotocatalytic degradation of contaminants of emerging concern: Functionalization, defect engineering, and heterojunctions

Contaminants of emerging concern (CECs), such as pharmaceuticals, in wastewater, poses significant risks to human health and ecosystems due to their persistence and bioaccumulation. To tackle this, tailored materials with enhanced properties are needed. Bismuth sulfur iodide (BiSI) is a promising sonocatalyst, but a poor photocatalyst, requiring modification strategies. This study explores four modification strategies for BiSI: (i) surface doping with silver ions to improve visible light absorption; (ii) defect engineering via sulfur vacancies to improve charge carrier separation; (iii) heterojunction formation with carbon nitride (C 3 N 4 ) to boost photocatalytic activity; and (iv) heterojunction formation with graphene oxide (GO) to increase surface area and adsorption. Each modification was fully characterized and applied to degrade carbamazepine (CBZ) via photocatalysis, sonocatalysis, and sonophotocatalysis. All modifications improved the removal efficiency across all methods, with GO@BiSI achieving the highest efficiency under sonophotocatalysis (90.4%). When comparing the efficiency of individual methods with the hybrid sonophotocatalytic approach, a noteworthy synergistic effect was observed. Catalysts modified with sulfur vacancies and C 3 N 4 exhibited synergy indices of 1.70 and 1.56, respectively, highlighting the superior efficiency and faster kinetics of the hybrid method compared to the sum of the individual methods. Degradation mechanisms were proposed to uncover degradation paths based on the modifications and remediation methods. These findings highlight the critical role of tailored modifications in improving the sonophotocatalytic activity, emphasizing a design-by-function strategy for developing high-performance catalysts, and paving the way for more efficient and sustainable solutions to address the persistent challenges posed by CECs in wastewater. • BiSI was modified by Ag, S vacancies, C 3 N 4 , and GO to enhance catalytic properties • GO@BiSI showed the highest CBZ removal efficiency under sonophotocatalysis (90.4%) • Distinct degradation pathways based on remediation method and modified catalyst • Strong synergy index in sonophotocatalysis for O-BiSI and C 3 N 4 @BiSI (1.70 and 1.56) • Tailored modifications enable an efficient and sustainable CBZ removal from water