Effects of peroxide types on the removal performance and mechanism of sulfonamide antibiotics using graphene-based catalytic membranes

This study reports in situ catalytic oxidation processes using graphene-based catalytic membranes to activate peroxydisulfate (PDS), peroxymonosulfate (PMS), and hydrogen peroxide (H2O2). Sulfonamide antibiotics in water, including sulfamethoxazole (SMX), sulfadiazine (SDZ), sulfamerazine (SMR), and sulfamethazine (SM2), were used as target pollutants. The composites of reduced graphene oxide and nitrogen-doped carbon nanotubes were loaded onto nylon microfiltration membranes at 8 g·m–2 mass dosage. The PDS-based systems exhibited the highest efficiency in removing SDZ (≥ 98%) and SMX (> 93%) during continuous 10 h filtration. In contrast, PMS was more suitable for oxidizing SMR (≥ 99%) and SM2 (≥ 90%) in a single pass. Based on functional group characterization and density functional theory calculations, structural defects and pyridinic/graphitic nitrogen species in carbon mats were identified as the main active centers for peroxide activation. Moreover, PDS, PMS and H2O2 exhibited distinct adsorption behaviors on defective and nitrogen-doped graphitic carbon, influencing the cleavage of peroxide bonds to generate reactive oxygen species. The reaction mechanism was investigated through electron paramagnetic resonance and chemical quenching tests. Surface-active species and singlet oxygen dominated in the PDS- and PMS-based systems, representing non-radical pathways, that selectively oxidize sulfonamides in real water matrices more effectively than the hydroxyl radicals involved in H2O2-based systems. PDS activating exhibited significant performance in organic fouling polishing, lowering the transmembrane pressure during continuous filtration. These findings offer valuable insights into implementing in situ catalytic oxidation processes in actual water purification.