Limited reduced graphene oxide incorporation into coffee ground-based biochar electroactive membranes: Enhanced electroactivity for efficient peroxymonosulfate activation and antibiotic removal

To explore the feasibility of enhancing the electroactivity of coffee ground biochar (CBC)-based carbon mats through controlled incorporation of reduced graphene oxide (rGO), various carbon mats consisting of powdered activated carbon (PAC), CBC, and rGO were fabricated and applied for the removal of representative antibiotics via peroxymonosulfate (PMS) activation under continuous filtration. The effects of the operational modes, water matrices, and target pollutant types on the performance of cathodic electroactive membranes were systematically investigated under limited carbon loading. Results indicated that non-radical singlet oxygen attack and surface-confined oxidation were the dominant pathways for target pollutant removal by CBC/rGO electroactive membranes. The membranes exhibited distinct oxidative selectivity, with a higher oxidation capacity for electron-donating group-bearing sulfonamides (sulfamethoxazole: 96.2% removal) than for electron-withdrawing group-bearing fluoroquinolones (levofloxacin: 62.6% removal) over a short contact time within the carbon mats, as evidenced by the removal efficiencies of both target pollutants and dissolved organic carbon. Density functional theory calculations and liquid chromatography-mass spectrometry analysis revealed that antibiotic degradation involves hydroxylation, C–N/C–O bond cleavage, and aromatic ring opening, which are closely correlated with the structural and electronic properties of the target pollutants. Notably, Ecological Structure-Activity Relationships toxicity predictions demonstrated that several degradation intermediates posed higher developmental and mutagenic toxicity risks than their parent compounds, thereby highlighting the necessity of regulating the oxidative selectivity in electroactive membranes and developing effective post-treatment processes for filtrates to mitigate such toxic risks.