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

Abstract

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-MnO2 (Ag-α-MnO2) 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 efficientdispersionof Ag increased thespecific surface area and pore volume of α-MnO2. The degradation experiments demonstrated that SMX could be efficiently degraded by a combination of PMS and Ag-α-MnO2 within 60 min. The apparent kinetic rate constant was 0.039 min−1, which was approximately ten times higher than that of α-MnO2. The impacts of external water conditions on catalytic performance and the stability of Ag-α-MnO2 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 SO4−, OH, O2− and 1O2. The two redox cycles of Ag+/Ag0 and Mn4+/Mn3+ on the surface of Ag-α-MnO2 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.