Facile synthesis of oxygen vacancies enriched α-Fe2O3 for peroxymonosulfate activation: A non-radical process for sulfamethoxazole degradation

Hematite (α-Fe 2 O 3 ) has been commonly used as an eco-friendly catalyst for peroxymonosulfate (PMS) to generate free radicals (SO 4 •- and/or •OH). However, the activation efficiency of PMS relies heavily on the conversion of Fe(III) to Fe(II) that is slow and rate-limiting. In this study, oxygen vacancies enriched α-Fe 2 O 3 was prepared from thermally treated goethite (α-FeOOH) and employed as a PMS activator. Systematic characterization demonstrated that α-Fe 2 O 3 with most abundant oxygen vacancies could be obtained by heating α-FeOOH at 300 °C. The as-prepared α-Fe 2 O 3 exhibited excellent catalytic activity in activation of PMS for oxidation of sulfamethoxazole (SMX, k  = 0.04 min −1 ). The SMX degradation rate was found to be positively correlated with the concentration of oxygen vacancies. Quenching experiments, EPR, LC/MS and XPS analysis revealed that singlet oxygen ( 1 O 2 ) was the predominant reactive oxygen species . The effects of pH, PMS dosage, catalyst loading, temperature, and anions on SMX degradation were comprehensively investigated. Moreover, the plausible degradation pathways of SMX in the α-Fe 2 O 3 /PMS system were proposed. This work not only provides a valuable insight into the mechanism of PMS activation by α-Fe 2 O 3 but also establishes a new strategy for the design of more efficient and practical iron-based catalyst for PMS activation.