Sliver-doped α-MnO2 to enhance peroxymonosulfate activation for efficient degradation of sulfamethoxazole: Cooperation between radical and non-radical mechanisms

The application of metal doping has emerged as a prominent approach for modifying transition-metal-based heterogeneous catalysts in activating peroxymonosulfate (PMS). Herein, silver-doped α-MnO 2 (Ag-α-MnO 2 ) was synthesized via a one-step hydrothermal approach and utilized for activating PMS to degrade sulfamethoxazole (SMX). The catalyst was systematically characterized and examined to determine that the efficient   dispersion   of Ag increased the   specific surface area and pore volume of α-MnO 2 . The degradation experiments demonstrated that SMX could be efficiently degraded by a combination of PMS and Ag-α-MnO 2 within 60 min. The apparent kinetic rate constant was 0.039 min −1 , which was approximately ten times higher than that of α-MnO 2 . The impacts of external water conditions on catalytic performance and the stability of Ag-α-MnO 2 were subsequently investigated. Density functional theory calculations revealed that Ag as a crucial active center reduced the PMS adsorption energy, promoted electron transfer, and orchestrated electron distribution. EPR spectra, quenching experiments, electrochemical tests, and XPS analysis were performed to validate the radical and non-radical mechanisms, including SO 4 − , OH, O 2 − and 1 O 2 . The two redox cycles of Ag + /Ag 0 and Mn 4+ /Mn 3+ on the surface of Ag-α-MnO 2 contributed to the activation of PMS. Additionally, probable degradation pathways for SMX were presented. This study provides an initially valuable insight into the cooperative mechanism of PMS activation for SMX degradation employing Mn-based catalysts doped with precious metal silver.