Acceleration of traces of Fe3+-activated peroxymonosulfate by natural pyrite: A novel cocatalyst for improving Fenton-like processes

The use of cocatalyst in Fenton-like reactions has been demonstrated as a reliable approach to improve their efficiency via accelerating the circulation of Fe3+/Fe2+. In this study, we for the first time used natural pyrite (FeS2) as a Fenton-like cocatalyst to improve the reactivity of Fe3+ instead of the widely investigated molybdenum disulfide that releases potential harmful molybdenum ions. The presence of FeS2 significantly improved the degradation of sulfamethoxazole (SMX) by Fe3+-peroxymonosulfate (PMS); near complete removal of SMX by FeS2-Fe3+-PMS was achieved, while no obvious removal of SMX by Fe3+-PMS was noticed. Meanwhile, the surface area-normalized rate constant of SMX degradation by FeS2-Fe3+-PMS was more than 18 times higher than that by MoS2-Fe3+-PMS. FeS2-Fe3+-PMS worked effectively in a wide range of pH values from 3.0 to 10.0. Although hydroxyl radicals, sulfate radicals, superoxide anion radicals, and singlet oxygen were recorded by electron paramagnetic resonance spectroscopy, only sulfate radicals were mainly responsible for the degradation. Sulfide ions were identified as one of the intermediates, but the reactive species generated by their interaction with PMS did not contribute to the degradation. FeS2 had a good stability by continually accelerating the circulation of Fe3+/Fe2+. The findings from this study reveal a highly efficient cocatalyst for Fenton-like reactions.