Regulation of surface-bound radicals enhanced Fenton-like activities via radicals confined on Fe3O4/MXenes.

The low yield and efficiency of surface-bound radicals seriously affect the Fenton-like activity of the catalyst. In this study, novel Fe3O4/MXenes (V2C and Ti3C2) composites are designed for structural domain regulation of surface-bound radicals. The MXenes with multilayer structure enhance the adsorption energy and electron transfer of the Fe3O4/peroxodisulfate (PDS) system. In the Fe3O4/V2C and Fe3O4/Ti3C2 systems, the adsorption energies of PDS at Fe sites are 8.27 and 4.36 eV, the electron transfer amounts are 0.303 and 0.115 e, and the lengths of the OO bond on PDS adsorbed are 2.965 and 1.503 Å, respectively. The enhanced adsorption and electron transfer properties make PDS more easily to be adsorbed on Fe3O4/V2C and broken to generate free radicals. The generated free radicals are confined to the structure of Fe3O4/V2C to form more surface-bound radicals, resulting in higher degradation efficiency. The contribution of surface-bound radicals to tetracycline (TC) degradation in Fe3O4/V2C/PDS reaches 45 %, while that of Fe3O4/Ti3C2/PDS is less than 15 %. The removal efficiency of Fe3O4/V2C-mediated surface-bound hydroxyl radical on TC reaches 93.3 % in 30 min, which is higher than that of Fe3O4/Ti3C2-mediated hydroxyl radical (•OH) and sulfate radical (SO4•-) (79.5 %). Fe3O4/V2C has excellent stability and reusability, and the surface-bound radicals produced by Fe3O4/V2C can degrade TC into non-toxic products. This study provides a new strategy for structural domain regulation of surface-bound radicals to enhance Fenton-like activities.