Holes-mediated photocatalytic activation of PDS for enhanced ifosfamide removal with MWCNTs-X/DBOB: role of Bi4O5Br2 and Bi24O31Br10 phases

Bismuth-rich oxybromide (Bi₄O₅Br₂) was modified with Multi-Walled Carbon Nanotubes (MWCNTs) functionalized with −H, –OH, and –COOH groups, which induced the appearance of Bi₂₄O₃₁Br₁₀ and Bi⁰ phases after solvothermal synthesis. This research aims to develop a sustainable, energy-efficient photocatalytic water purification system to enhance PDS activation and persistent organic pollutants removal. The efficiency of solar-driven photocatalytic persulfate activation and removal of the cytostatic drug ifosfamide (IF) in the presence of MWCNTs-X/DBOB (where DBOB = Bi₂₄O₃₁Br₁₀-Bi₄O₅Br₂; X=H, OH, COOH) was investigated. A heterojunction formed between Bi₂₄O₃₁Br₁₀ and Bi₄O₅Br₂, resulting in effective hole-mediated activation of PDS by Bi₂₄O₃₁Br₁₀ and the generation of O₂^•− by Bi₄O₅Br₂, while MWCNTs and metallic Bi served as electron sinks. The spatial separation of photogenerated charge carriers facilitated efficient PDS activation, particularly using MWCNTs-H/DBOB as a photocatalyst. In PDS-assisted photocatalysis, hydroxyl radicals predominantly played a crucial role in IF removal at pH 6.7, while at pH 3, sulfate and hydroxyl radicals were the main contributors to IF decomposition. Theoretical calculations showed that ^•OH and SO₄^•- radicals decomposed IF by H abstraction, whereas the SET pathway was favorable for SO₄^•- radicals. The presence of inorganic ions (Cl^-, NO₃^–, HPO₄^2-, HCO₃^–) inhibited IF decomposition by adsorption at the photocatalyst surface, while humic acids enhanced IF degradation, facilitating the PDS activation through energy absorption and electron transfer. In further studies, we will evaluate 2.5 %MWCNTs-X/DBOB reusability under continuous operation conditions.