The Pivotal Role of Selenium Vacancies in Defective FeSe2@MoO3 for Efficient Peroxymonosulfate Activation: Experimental and DFT Calculation

The presence of selenium vacancies (VSe) in metal selenides enables the activation of peroxymonosulfate (PMS) for efficient water purification. However, the mechanisms of interactions of VSe with PMS and organic pollutant removal are unclear. Hence, we precisely prepared a series of FeSe2@MoO3 composites with VSe for effective activation of PMS for the removal of various organic pollutants. The roles of VSe are explored via density functional theory (DFT) calculations: (i) regulating the electron distribution of Fe and Mo orbitals in FeSe2@MoO3 for enhancing the PMS adsorption and (ii) promoting the conversion of transition metallic redox pairs (Fe3+/Fe2+ and Mo6+/Mo5+/Mo4+). The as-prepared FeSe2@MoO3-8 exhibits excellent catalytic performance via PMS activation in which nearly 100% removal efficiencies of various organic pollutants are achieved within 2–10 min. The quenching experiments, electronic spin resonance (ESR), and probe tests demonstrated that the multiple reactive species like SO4•–, O2•–, •OH, and 1O2 contributed to the removal of 2,4-D. Finally, FeSe2@MoO3-8 was attached to the polyvinylidene difluoride (PVDF) membrane for continuous and efficient removal of 2,4-D, in which the removal efficiency and total organic carbon removal efficiency of 2,4-D were > 90% and >70% within 12 h of operation.