Producing OH, SO4− and O2− in heterogeneous Fenton reaction induced by Fe3O4-modified schwertmannite

Abstract Heterogeneous Fenton has become a promising economical and environmentally-friendly method for water treatment, however, the production of abundant radical resources (e.g., •O2-, •OH) are oftentimes limited by finite Fe2+ species to activate H2O2. Therefore, development of a new iron-bearing solid modified with diverse functional groups for generating a large of radicals in heterogeneous Fenton is significance. Here, we constructed a Fe3O4-modified schwertmannite (Fe3O4/Sch) catalyst to activate H2O2, SO42- and O2 to produce three kinds of radicals in heterogeneous Fenton reaction. Specifically, Fe3O4/Sch catalyst was synthesized to improve its surface properties such as the contents of surface Fe2+ species as H2O2 or O2 activators to produce •OH or •O2-, the SO42- of Sch surface as SO4•- precursor, and electron transfer between ≡Fe3+ and ≡Fe2+. Degradation rate of ciprofloxacin (CIP) for 6 min was up to 97% in Fe3O4/Sch-H2O2 system, which was higher than that in Sch-H2O2 or Fe3O4-H2O2. After four successive cyclic experiments, degradation rate of CIP was still achieved 97% within 10 min in Fe3O4/Sch-H2O2 system. The formation pathways of the relevant active radicals and the degradation pathways of CIP were also proposed by theoretically calculated and LC-MS data. This finding has not only developed an efficient heterogeneous Fenton catalyst, but also given a new idea of SO4•- generation by modified iron oxyhydroxysulfate mineral for application of heterogeneous Fenton technology.