Single-atom iron catalysts on defect-rich nitrogen-doped carbon nanosheets for efficient phenol degradation via peroxydisulfate activation
Phenolic compounds are typical refractory organic pollutants in coal chemical coking wastewater, posing significant risks to ecosystems and human health. Conventional treatment methods are inefficient, necessitating advanced oxidation processes (AOPs). Here, we report a low-cost Fe/N–C catalyst synthesized from coal-tar pitch, a common by-product of the coal chemical industry, via a self-assembly and pyrolysis strategy using graphitic carbon nitride (g-C3N4) as a template and nitrogen source, with dicyandiamide as an auxiliary nitrogen source and FeCl3·6H2O as the iron precursor. The resulting nitrogen-doped carbon nanosheets possess abundant defects (sp3-C/sp2-C = 0.66) and atomically dispersed iron species. The Fe/N–C catalyst exhibits outstanding catalytic activity for peroxydisulfate (PDS) activation, achieving over 98% phenol degradation within 30 minutes and a 60% total organic carbon (TOC) removal rate. Mechanistic studies, including radical quenching and electron paramagnetic resonance (EPR) experiments, reveal that both radical and non-radical pathways contribute to phenol degradation, with singlet oxygen (1O2) as the primary reactive oxygen species. Electrochemical analyses demonstrate that atomically dispersed Fe sites significantly enhance interfacial electron transfer. Post-reaction characterization indicates the consumption of pyrrolic-N, C=O, and carbon defects as active sites, while graphitic-N and Fe–N structures remain stable, confirming the catalyst's stability. This work provides an economical route to convert coal-tar pitch into high-performance catalytic materials for efficient water treatment, embodying the circular economy concept of waste-to-resource utilization.