l-cysteine-modified Fe₃ O₄ nanoparticles as a novel heterogeneous catalyst for persulfate activation on BTEX removal

l-cysteine-modified Fe₃ O₄ nanoparticles (l-cys@nFe₃ O₄ ) were synthesized successfully and used as catalyst to activate persulfate (PS) for benzene, toluene, ethylbenzene, and xylenes (BTEX) degradation. The composite was fully characterized, and the l-cys@nFe₃ O₄ had more protrusions and l-cys was combined on the surface of nFe₃ O₄ . The removals of BTEX were 78.2%, 85.1%, 85.3%, 81.2%, respectively, in PS/l-cys@nFe₃ O₄ system, while only 52.7% 57.8%, 60.8%, and 56.3% of BTEX removals reached under the same condition for nFe₃ O₄ chelated with l-cys in 48 h. Four successive cycles of BTEX degradation were completed in PS/l-cys@nFe₃ O₄ system. The synergistic mechanisms of BTEX degradation in PS/l-cys@nFe₃ O₄ system were investigated by electron paramagnetic resonance (EPR), benzoic acid (BA) probe and X-ray photoelectron spectroscopy (XPS) tests. SFe bond in l-cys-Fe complexes promoted the electron transfer between nFe₃ O₄ core and the solution, iron and iron at the interface, thereby promoting the Fe³⁺ /Fe²⁺ cycle and the catalytic capacity of nFe₃ O₄ . The optimal pH of PS/l-cys@nFe₃ O₄ system was 3, while HCO₃ ^- and Cl^- exhibited negative influences on BTEX degradation. Only 14.2%, 15.5%, 15.9%, and 15.6% BTEX had been removed in the presence of 0.12-M PS and 8.0 g/L l-cys@nFe₃ O₄ under the actual groundwater condition. However, expanding the dosage of PS and l-cys@nFe₃ O₄ was an effective strategy to overcome the adverse effect. PRACTITIONER POINTS: L-cys@nFe₃ O₄ were synthesized successfully and used as catalyst to activate PS for BTEX degradation. Four successive cycles of BTEX degradation were completed in PS/L-cys@nFe₃ O₄ system. lS-Fe bond in L-cys@nFe₃ O₄ promoted the electron transfer between PS and nFe₃ O₄ core.