Fe/Mn-doped Chlorella biochar for enhanced metronidazole degradation via PMS activation: mechanistic insights into catalytic performance†

Fe/Mn-doped Chlorella biochar (Fe/Mn–BC) was successfully synthesized and applied to the degradation of the antibiotic metronidazole (MNZ) through peroxymonosulfate (PMS) activation. Characterization results revealed that the modified Fe/Mn–BC exhibited a significant increase in total pore volume and specific surface area compared to the pristine biochar. Under optimized conditions, the Fe/Mn–BC+PMS system achieved a remarkable removal efficiency of 94.3% for MNZ. The degradation process involved both free radical (e.g., sulfate radicals SO₄˙⁻ and hydroxyl radicals ˙OH) and non-free radical pathways, as confirmed by quenching experiments and electron paramagnetic resonance (EPR) analysis. The Fe/Mn–BC catalyst demonstrated excellent reusability and stability over multiple cycles, highlighting its practical applicability. Mechanistic studies indicated that the degradation of MNZ primarily occurred through bond cleavage and ring-opening reactions induced by radical attack. Ecotoxicity assessments revealed an increase in the LC₅₀ values of intermediate products for Daphnia magna, along with a reduction in the bioconcentration factor and mutagenicity index, suggesting effective mineralization and a significant decrease in the environmental risks associated with MNZ. This study not only provides a sustainable approach for antibiotic pollutant removal but also achieves simultaneous waste utilization and environmental remediation, offering a promising strategy for water treatment applications.