N-doped graphene loaded with Ru sites as PMS activators for SMX degradation via non-radical pathway: efficiency, selectivity and mechanism

Abstract

The degradation of sulfamethoxazole (SMX) by advanced oxidation processes (AOPs) based on peroxomonosulfate (PMS) represents an effective and environmentally friendly approach to the elimination of sustainable pollution. In this study, an N-doped graphene activator loaded with Ru (N-rGO-Ru) active sites was synthesized by a onepot method. The Ru in N-rGO-Ru exists in the form of cluster bonds, and Ru-N bonds were formed. Under optimized conditions, (0.02 g·L⁻¹) N-rGO-Ru removed 92 % of SMX, rate constant (k = 0.0214 min⁻¹) in 120 min by a non-radical pathway mediated by singlet oxygen (¹O₂), as evidenced by quenching experiments and electron paramagnetic resonance (EPR) spectroscopy. The catalyst of N-rGO-Ru demonstrated exceptional tolerance to coexisting anions (e.g., Cl⁻, HCO₃⁻) and maintained 80 % efficiency after five cycles while minimizing metal leaching (<16 μg·L⁻¹), highlighting its robust stability and reusability. (Liquid Chromatograph Mass Spectrometer) LC–MS analysis identified four degradation pathways, including hydroxylation, sulphonamide bond cleavage, ring-opening, and coupling reactions, with ECOSAR modelling confirming significantly reduced acute and chronic toxicity of intermediates compared to SMX Theoretical calculations demonstrated that the Ru-N site enhanced the adsorption energy (−4.8 eV) and electron transfer efficiency of PMS, thereby facilitating efficient activation. The findings of this study indicate the capability of Ru-based materials to be utilized in the effective removal and detoxification of SMX in wastewater.