Mo Vacancy-Mediated Activation of Peroxymonosulfate for Ultrafast Micropollutant Removal Using an Electrified MXene Filter Functionalized with Fe Single Atoms

Developing advanced heterogeneous catalysts with atomically dispersed active sites is an efficient strategy to boost the kinetics of peroxymonosulfate (PMS) activation for micropollutant removal. Here, we report a binary Mo₂TiC₂T_x MXene-based electroactive filter system with abundant surface Mo vacancies for effective activation of PMS. The Mo vacancies assumed two essential roles: (i) as anchoring sites for Fe single atoms (Fe-SA) and (ii) as cocatalytic sites for the Fenton-like reaction. Fe-SA formed strong metal-oxygen bonds with the Mo₂TiC₂T_x support, stabilizing at the sites previously occupied by Mo. The resulting Fe-SA/Mo₂TiC₂T_x nanohybrid filter achieved 100% degradation of sulfamethoxazole (SMX) in the single-pass mode (hydraulic retention time <2 s) when assisted by an electric field (2.0 V). The rate constant (k = 2.89 min^-1) for SMX removal was 24 and 67 times greater than that of Fe nanoparticles immobilized on Mo₂TiC₂T_x and the pristine Mo₂TiC₂T_x filter, respectively. Operation in the flow-through configuration outperformed the conventional batch reactor model (k = 0.17 min^-1) due to convection-enhanced mass transport. The results obtained from experimental investigations and theoretical calculations suggested that atomically dispersed Fe-SA, anchored on Mo vacancies, was responsible for the adsorption and activation of PMS to produce sulfate radicals (SO₄^•-) in the presence of an electric field. This study provides a proof-of-concept demonstration of an electroactive Fe-SA/Mo₂TiC₂T_x filter for broader application in the treatment of water contaminated by emerging micropollutants.