Enhanced degradation of bisphenol S by persulfate activated with sulfide-modified nanoscale zero-valent iron

Sulfide-modified nanoscale zero-valent iron (S-nZVI) has been considered an efficient material to remove heavy metals and organic contaminants. The experiments of bisphenol S (BPS) degradation by persulfate (PS) activated with S-nZVI (S-nZVI/PS) or nZVI (nZVI/PS) were carried out in this paper. The results show that, compared to the bare nZVI/PS system, the S-nZVI/PS system shows higher activity in BPS degradation, especially at high BPS concentration. The reaction rate constant k_obs of BPS removal by the S-nZVI/PS system (0.142 min^-1) was much higher than that in nZVI/PS system (0.089 min^-1) because more oxidation species were generated in the S-nZVI/PS system. The results of electron paramagnetic resonance (EPR) and radical quenching tests show that both hydroxyl radical (·OH) and sulfate radical (SO₄^·-) were involved in the degradation of BPS and had a great contribution to BPS removal. Moreover, the effects of S/Fe molar ratio, S-nZVI dosage, initial pH, and initial concentration of PS or BPS on S-nZVI/PS were also studied. The results show that the S/Fe molar ratio has significant influence on the BPS degradation; over 97.7% of the removal efficiency was achieved at 0.035 of S/Fe molar ratio. And the removal efficiency of BPS degradation increased with the increase of the dosage of S-nZVI, PS concentration. Furthermore, BPS could be efficiently removed in solutions with a wide range of initial pH (3.13-9.35). The observed results show that it is promising in the removal of micro-pollutants from water by persulfate activated with S-nZVI.