Junction of phase-controlled MnO and MnFeO with optimal built-in electric field and multi-active sites for efficient peroxymonosulfate activation toward environmental remediation.

The non-homogeneous catalysts have been widely employed for the treatment of organic pollutants in complex water environments. However, the recovery of the catalysts, the secondary contamination of metal ions and the catalytic activity of the catalysts remain significant challenges. Accordingly, the crystalline structure of highly active MnO were be modulated and combined it with strongly magnetic MnFeO to activate peroxymonosulfate (PMS) for tetracycline (TC) degradation. The removal efficiency of TC by β-MnO/MnFeO within 20 min is achieved to be 92.5 %, which is higher than that of pure MnFeO and β-MnO. To further investigate the actual treatment capacity of β-MnO/MnFeO, a fixed-bed system was established, which showed stable removal efficiency of TC could reach 93 % at 350 h of continuous degradation. The heterojunction construction creates a built-in electric field (BIEF) at the interface, enabling directional electron transfer, and the presence of multiple active sites ensures structural stability (the ion leaching amount was in accordance with the standard) by limiting the electron gain and loss during degradation. The relative contributions of ·OH, SO, O, and other active species (O and direct electron transfer) to the overall degradation process were calculated as 1.01 %, 6.59 %, 37.5 %, and 54.9 %, respectively. Moreover, the heterojunction construction enhanced the adsorption capacity of the catalyst on PMS molecules (E = -2.925 eV), as well as solved the catalyst recycling problem. The system has good stability, recoverability and wide range of pollutant degradation ability, which provides a new strategy for PMS activation and the construction of BIEF.