l-cysteine-modified Fe3O4 nanoparticles as a novel heterogeneous catalyst for persulfate activation on BTEX removal

l -cysteine-modified Fe 3 O 4 nanoparticles ( l -cys@nFe 3 O 4 ) 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@nFe 3 O 4 had more protrusions and l -cys was combined on the surface of nFe 3 O 4 . The removals of BTEX were 78.2%, 85.1%, 85.3%, 81.2%, respectively, in PS/ l -cys@nFe 3 O 4 system, while only 52.7% 57.8%, 60.8%, and 56.3% of BTEX removals reached under the same condition for nFe 3 O 4 chelated with l -cys in 48 h. Four successive cycles of BTEX degradation were completed in PS/ l -cys@nFe 3 O 4 system. The synergistic mechanisms of BTEX degradation in PS/ l -cys@nFe 3 O 4 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 nFe 3 O 4 core and the solution, iron and iron at the interface, thereby promoting the Fe 3+ /Fe 2+ cycle and the catalytic capacity of nFe 3 O 4 . The optimal pH of PS/ l -cys@nFe 3 O 4 system was 3, while HCO 3 − 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@nFe 3 O 4 under the actual groundwater condition. However, expanding the dosage of PS and l -cys@nFe 3 O 4 was an effective strategy to overcome the adverse effect. Practitioner Points L-cys@nFe 3 O 4 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@nFe 3 O 4 system. lS―Fe bond in L-cys@nFe 3 O 4 promoted the electron transfer between PS and nFe 3 O 4 core.