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

• Published in: Journal of water process engineering 2024-07, Vol.64, p.105574, Article 105574
• Main Authors: Su, Yinmei, Sun, Wei, Yuan, Lizhu, Yang, Wenchao, Zhang, Qichun, Wong, Jonathan W.C.
• Format: Article
• Language: English
• Subjects: Advanced oxidation processes; Interstitial N site; Nitrogen anion doping; Peroxymonosulfate; Singlet oxygen
• ISSN: 2214-7144; 2214-7144
• DOI: 10.1016/j.jwpe.2024.105574

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 MnOx 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 kobs (0.1067 min−1) was 16.1- and 12.4-folds higher than that of raw ɛ-MnO2 (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 1O2. 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 K2Cr2O7-induced inhibition was attributed to the catalytic site consumption of N-Mn-300 by K2Cr2O7, rather than K2Cr2O7-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. [Display omitted] •Nitrogen doping greatly enhances the ability of MnO2 to activate peroxymonosulfate.•BPA removal rate of 99.8% and mineralization rate of 87.8% are achieved.•Electron loss of Mn neighboring interstitial N atom promotes the catalysis.•Catalytic mechanism of MnII→˙OH/SO4˙−MnIII←O12MnIV is proposed.•K2Cr2O7 inhibition was due to catalytic site consumption of N-Mn-300 rather than quenching free electron.