Mo Vacancy-Mediated\nActivation of Peroxymonosulfate\nfor Ultrafast Micropollutant Removal Using an Electrified MXene Filter\nFunctionalized with Fe Single Atoms

Abstract

Developing advanced heterogeneous catalysts with atomically\ndispersed\nactive sites is an efficient strategy to boost the kinetics of peroxymonosulfate\n(PMS) activation for micropollutant removal. Here, we report a binary\nMo₂TiC₂T<i>_x</i> MXene-based\nelectroactive filter system with abundant surface Mo vacancies for\neffective activation of PMS. The Mo vacancies assumed two essential\nroles: (i) as anchoring sites for Fe single atoms (Fe-SA) and (ii)\nas cocatalytic sites for the Fenton-like reaction. Fe-SA formed strong\nmetal–oxygen bonds with the Mo₂TiC₂T<i>_x</i> support, stabilizing at the sites previously\noccupied by Mo. The resulting Fe-SA/Mo₂TiC₂T<i>_x</i> nanohybrid filter achieved 100% degradation\nof sulfamethoxazole (SMX) in the single-pass mode (hydraulic retention\ntime <2 s) when assisted by an electric field (2.0 V). The rate\nconstant (<i>k</i> = 2.89 min^–1) for SMX\nremoval was 24 and 67 times greater than that of Fe nanoparticles\nimmobilized on Mo₂TiC₂T<i>_x</i> and the pristine Mo₂TiC₂T<i>_x</i> filter, respectively. Operation in the flow-through configuration\noutperformed the conventional batch reactor model (<i>k</i> = 0.17 min^–1) due to convection-enhanced mass\ntransport. The results obtained from experimental investigations and\ntheoretical calculations suggested that atomically dispersed Fe-SA,\nanchored on Mo vacancies, was responsible for the adsorption and activation\nof PMS to produce sulfate radicals (SO₄^•–) in the presence of an electric field. This study provides a proof-of-concept\ndemonstration of an electroactive Fe-SA/Mo₂TiC₂T<i>_x</i> filter for broader application in\nthe treatment of water contaminated by emerging micropollutants.