Room-temperature induction of oxygen vacancies in Bi2Fe4O9 for PMS activation and dimethyl phthalate degradation: Mechanism and toxicity evaluation

Abstract

Advanced oxidation processes involving the activation of persulfate offer an effective approach for mitigating environmental pollution caused by dimethyl phthalate (DMP). In this study, a heterogeneous catalyst enriched with oxygen vacancies for peroxymonosulfate (PMS) activation was prepared by simultaneously subjecting Bi₂Fe₄O₉ to acid etching and light irradiation. The resultant material, designated as BFO-LA, was optimized by varying the acid etching concentrations to achieve the most efficacious degradation of DMP (10 mg/L). Comprehensive characterization techniques revealed the structural characteristics and presence of oxygen vacancies in BFO-LA. Results showed that the Fe²⁺ sites in BFO-LA activate PMS to generate active species, with singlet oxygen and free radicals playing key roles in DMP degradation. In the system of 0.3 mg/L BFO-LA and 1 mM PMS, it can degrade 94.7 % of DMP in 60 min, with the degradation kinetic constant of 0.0542 min⁻¹. Oxygen vacancies enhanced electron transfer and the Fe³⁺/Fe²⁺ redox cycle, improving PMS activation efficiency from 9.7 % to 88.3 %, compared to unmodified Bi₂Fe₄O₉. Notably, the BFO-LA catalyst retained its superior stability and catalytic activity even upon repeated use. After 6 cycles of experiments, the degradation efficiency of DMP was still as high as 94.1 %. Toxicity evaluations utilizing the T.E.S.T. software and rice seedlings demonstrated that the degradation process effectively mitigated the toxicity associated with DMP, alleviating the adverse effects on seed germination and seedling growth. Collectively, this study highlights the significance of oxygen vacancies in BFO-LA, establishing it as an efficient and stable PMS activation catalyst for DMP degradation