Synergy of biochar-supported iron single-atom self-motivated catalysis and biochar-induced adsorption enables...

Dual-reaction-center catalytic systems enable self-motivated pollutant degradation without external oxidants, where "self-motivated" refers to pollutant transformation driven by pollutant-to-catalyst interfacial electron transfer. However, their limited pollutant-enrichment capacity and inefficient interfacial electron transfer often necessitate high catalyst loadings, compromising economic viability. Moreover, the role of adsorption enrichment in regulating self-motivated electron transfer remains insufficiently understood. To address these limitations, a biochar-supported iron single-atom catalyst (Fe_SAC/NC) with FeN₃/FeN₄-type coordination environments was developed to couple pollutant enrichment with self-motivated catalytic transformation. At an ultralow catalyst loading, Fe_SAC/NC achieved rapid TAP removal without added oxidants and maintained robust performance across varying pH conditions and complex ionic matrices. In addition, Fe_SAC/NC showed effective removal of diverse emerging contaminants. Contribution analysis indicated that adsorption was the largest individual contributor to TAP removal (47%), followed by electron transfer (30%) and dissolved oxygen (23%), with the latter two collectively accounting for 53% through self-motivated transformation. Porous biochar enriched TAP near active centers through electrostatic and π-π interactions, while FeN₃/FeN₄-associated electronic heterogeneity promoted interfacial charge redistribution and electron transfer from TAP to Fe centers. ECOSAR predictions indicated differences in toxicity among transformation products, while plant cultivation experiments supported alleviated phytotoxicity under the tested conditions. Continuous-flow and real-water tests demonstrated operational robustness. Life cycle assessment indicated lower environmental impacts than a conventional Fenton-type process using peroxymonosulfate. This study provides a basis for developing scalable and sustainable water treatment processes without added oxidants.