Nitrogen-modified manganese oxide activated peroxymonosulfate for pollutant degradation: Primary role of interstitial N sites

Nitrogen anion doping has been considered as an effective strategy to modulate the electronic structure of transition metal oxides and improve their catalysis. However, the roles of interstitial and substitutional N sites in PMS activation remained be unclear. To address this issue, N-doped MnO x with different N configurations were synthesized through calcining their precursors at different temperatures with urea. The incorporation of N atom into manganese oxide lattice remarkably enhanced the catalytic activity. Correspondingly, N-Mn-300/PMS system obtained a removal rate of 99.8% and mineralization rate of 87.8%, whose k obs (0.1067 min −1 ) was 16.1- and 12.4-folds higher than that of raw ɛ -MnO 2 (0.0066 min −1 ) and Mn-300 (0.0086 min −1 ). Such promotion was mainly attributed to the decreased electron cloud density of Mn neighboring interstitial N atom, which provided a driving force to induce transfer electron from PMS to Mn, subsequently causing PMS oxidation into 1 O 2. By contrast, the substitutional N increased the electron density of Mn and exhibited a minor promotion effect in the enhanced catalysis. A possible catalytic mechanism of MnII→˙OH/SO4˙−MnIII←O12MnIV was proposed. Notably, it was newly discovered that this K 2 Cr 2 O 7 -induced inhibition was attributed to the catalytic site consumption of N-Mn-300 by K 2 Cr 2 O 7, rather than K 2 Cr 2 O 7 -quenching free electron. This work highlights the primary role of interstitial N site in regulating the electronic structure of manganese oxide to strengthen peroxymonosulfate activation.