Bismuth nanospheres enabling sacrificial-agent-free bromate photoreduction and total bromine mitigation for safer water treatment.

Zero-valent bismuth (Bi) nanospheres with a hollow structure were synthesized via a polyvinylpyrrolidone (PVP)-assisted solvothermal method and applied as efficient photocatalysts for the sacrificial-agent-free photoreduction of bromate (BrO) under ultraviolet (UV) irradiation. The optimized Bi-0.6 catalyst exhibited a narrowed band gap and enhanced charge separation efficiency, achieving 99.5 % BrO removal within 30 min at neutral pH. Comprehensive photoelectrochemical analysis revealed that the in-situ self-oxidation of Bi to Bi served as an intrinsic hole scavenging pathway, suppressing charge recombination and sustaining electron availability without needing external reductants. In addition to the rapid reduction of BrO, a significant decrease in total bromine concentration was observed, which is attributed to the incorporation of bromide (Br) into BiOBr crystalline phases, effectively mitigating the risk of secondary disinfection byproducts. The Bi-0.6 nanospheres also exhibited excellent stability and recyclability over multiple reaction cycles and retained high activity in real water (RW) matrices containing organic matter and competing anions. These results highlight the dual functionality of zero-valent Bi nanospheres in enabling efficient pollutant removal and total bromine mitigation through a self-regulating photocatalytic process. This work presents a sustainable and practical strategy for BrO remediation and provides insights into the design of environmentally compatible photocatalytic systems for safe water treatment applications.