Atomically Dispersed Fe-Modified SnS for Sn-Centered Peroxymonosulfate Activation Toward Acetaminophen Degradation

SnS is a low-cost and environmentally benign semiconductor for photocatalysis and piezocatalysis, but its direct use for peroxymonosulfate (PMS) activation remains limited. Here, we develop a facile Fe substitution strategy to construct atomically dispersed Fe‒S in SnS nanostructures (Fe-SnS) for efficient PMS activation. The catalytic activity shows a volcano-shaped dependence on Fe incorporation, with 5% Fe-SnS (Fe/Sn molar ratio of 4.63%) giving the optimal performance, achieving efficient acetaminophen (APAP) removal with a rate constant of 1.23 min^‒1, which is 3.84 and 176-fold higher than those of SnS and commercial SnS, respectively. In situ X-ray absorption spectroscopy reveals a site-dependent activation mechanism in which Sn sites directly coordinate with O in PMS. Density functional theory calculations further show that Fe incorporation induces local electronic redistribution around neighboring Sn sites and enhances the Sn-PMS interfacial interaction. Fe incorporation also attenuates the negative surface charge of SnS, further facilitating PMS interaction. Mechanism studies revealed that APAP degradation proceeds via sulfate and hydroxyl radical-dominated pathway. These findings clarify the distinct roles of host Sn and atomically dispersed Fe sites in PMS activation.