Enhanced simazine degradation via peroxymonosulfate activation using hemin-doped rice husk biochar as a novel Fe/N–C catalyst

The presence of herbicides, including simazine (SIM), in aquatic environments pose significant threats to these ecosystems, necessitating a method for their removal. In this study, a hemin-doped rice husk-derived biochar (RBC@Hemin_20%) was synthesized using a simple, one-step pyrolysis, and its degradation efficiency towards SIM via peroxymonosulfate (PMS) was assessed. Under optimized conditions (hemin loading = 20 wt%, SIM = 0.5 ppm, RBC@Hemin_20% catalyst = 0.2 g L⁻¹, PMS = 2.0 mM, and pH = 5.84 [unadjusted]), RBC@Hemin_20%, as an Fe/N–C catalyst, could activate PMS to achieve >99% degradation of SIM. Based on radical scavenger and electron spin resonance spectroscopy (ESR) experiments, both radical (^•OH and SO₄^•−) and non-radical (such as singlet oxygen, ¹O₂) mechanisms and electron transfer were involved in the degradation system. Significant mineralization (97.3%) and reusability efficiency (∼74.1% SIM degradation after 4 applications) were exhibited by the RBC@Hemin_20%/PMS system, which also maintained a remarkable degradation efficiency in tap-, river-, and ground-water. Additionally, the RBC@Hemin_20%/PMS system exhibited rapid degradation of tetracycline (TC) and diclofenac (DCF), indicating its prospects in the degradation of other organic pollutants of aquatic environments. The plausible degradation mechanism pathways of SIM are proposed based on identified intermediates. Finally, the toxicity of these intermediate products is analysed using the Ecological Structure Activity Relationship (ECOSAR) software. It is expected that this study will expand the current knowledge on the synthesis of efficient biomass-based Fe/N–C composites for the removal of organic pollutants in water.