Efficient sulfamethoxazole degradation via staged PMS activation on magnetic pyrite–biochar: Enhanced mineralization and mechanism

Peroxymonosulfate (PMS)-based advanced oxidation processes often suffer from unstable activation and low mineralization efficiency when treating sulfamethoxazole (SMX). Herein, a magnetic pyrite–biochar (600MRSC₁) derived from reed straw and pyrite was synthesized and implemented in a sequential non-radical–radical pathway (SNRP) system. The SNRP-600MRSC₁/PMS system rapidly rapidly achieved near-complete SMX removal (>99%, within the detection limit) and a total organic carbon reduction of 72.8%, which was 2.17 times higher than that of the 600MRSC₁/PMS system. Mechanistic investigations revealed that PMS degraded SMX via hydroxylation in Stage 1, while the resulting intermediates were further mineralized in Stage 2 by radicals generated from PMS activation by 600MRSC₁, mainly SO₄·^- (41.22%) and ·OH (32.06%). The presence of S(II) promoted the generation of low-valent Fe species and accelerated Fe (II)/Fe (III) cycling, ensuring stable catalytic activity. The system also achieved complete SMX removal in tap and river water and maintained stable performance in five-cycle reuse experiments, showing strong applicability in real water matrices. This work provides a biochar-based strategy for improving PMS activation stability and achieving deep mineralization of organic pollutants.