Elucidating multiple reaction pathways for the degradation of antibiotics in water by a self-active single-atom zinc catalyst on biochar

Single-atom catalysts (SACs) have gained notable attention for the degradation of organic contaminants in water. However, most previous studies focused on the activation of peroxymonosulfate (PMS) or peroxydisulfate (PDS) for contaminant removal. Herein, we demonstrated for the first time that a Zn single-atom catalyst supported on biochar (SAZn@BC) alone removed ∼98.0% of trimethoprim (TMP) within 30 minutes. The catalyst was synthesized via a simple pyrolysis process using oak wood powder as the feedstock. Detailed characterization of the catalyst demonstrated the single-atom Zn2+ valence state and the Zn–N4 local coordination structure, as well as abundant redox active oxygen functional groups on biochar. The coordination between Zn single atoms and the oxygen functional groups resulted in multiple reaction pathways for TMP degradation, including both reactive oxygen species-enabled degradation and direct oxidation. The Zn single atom in SAZn@BC was a necessary electron shuttling bridge for both pathways. Density functional theory (DFT) calculations supported the spontaneous occurrence of the proposed reactions in the system. Overall, our results showed that SAZn@BC alone can be a promising catalyst for a healthy and sustainable environment by removing contaminants in water effectively without any chemical or light energy input.