Molybdenum nitride(γ-Mo2N) as a novel co-catalyst to enhance Fe(III)/Fe (II) cycle for homogeneous and heterogeneous peroxymonosulfate activation: Performance and mechanism

In this work, molybdenum nitride (gamma-Mo2N) was investigated for the first time as a co-catalyst to accelerate the activation of PMS by enhancing iron cycling for the treatment of acid orange 7. gamma-Mo2N/PMS/Fe3+ system showed excellent performance: 95% of acid orange 7 were highly degraded within 9 mins, and the gamma-Mo2N proved to be stable and reusable after a 4-cycles experiment. The homogeneous Fe2+-activated PMS process was determined by testing the change in the concentration of iron species during the experiments. In addition, the heterogeneous activation of PMS by the iron retained on the catalyst surface was further determined by ICP-OES and the degradation effect of the *gamma-Mo2N (used gamma-Mo2N)/PMS system. In addition, the main active species for the homogeneous and heterogeneous activation of the PMS process were identified as hydroxyl radicals(.OH), sulfate radicals (SO4.-) and singlet oxygen (1O2) by EPR tests. Based on XPS, TEM and FT-IR analyses, a possible mechanism was proposed: Mo(III) and Mo(IV) play the role in the reduction of Fe3+, and gamma-Mo2N forms Mo-N-OFe as well as Mo-N-Fe electron-transfer processes with iron in the reaction, which correspond to heterogeneous and homogeneous activation for PMS to achieve efficient degradation of the target. In summary, this work clarifies that gamma-Mo2N can act as an efficient co-catalyst in the gamma-Mo2N/PMS/Fe3+ system to accelerate the Fe(III)/ Fe(II) cycle and thus promote homogeneous and heterogeneous PMS activation, which provides a promising gamma-Mo2N co-catalyzed AOPs for rapid and efficient abatement of organic contaminants.