Nitrogen-doped nanocarbon derived from candle soot for persulfate activation on sulfamethoxazole removal: Performance and mechanism

Recently, carbon materials have attracted much attention in activating persulfate (PS) for the removal of organic pollutants. Seeking a greener, lower-cost, and higher-performance carbon material has become an important aspect of research. In this study, candle soot was innovatively used as a nanocarbon material, and its performance for PS activation was improved by simple ammonium ferric citrate modification. The optimal catalytic performance was achieved using 0.15 g/L modified candle soot (AS) and only 0.1 mM PS, with sulfamethoxazole (SMX) removal efficiency up to 95.5% within 120 min. Quenching tests, together with electron paramagnetic resonance measurements, showed that O2- and 1O2 were the main reactive species for SMX degradation. Meanwhile, electron transfer pathway was also occurred. Various characterization results showed that graphitic N and carbonyl group were the main active sites for PS activation. Moreover, AS/PS system exhibited high catalytic activity and stability for SMX degradation over a wide initial pH range (3∼9), or even in the presence of Cl-, H2PO4- and NO3-. This work not only taps the potential of candle soot as an environmental functional material, but also showcases the roadmap for the discovery, design, and resource utilization of other waste carbon materials in wastewater treatment.