Molten salt-templated synthesis of Fe-N5 sites on ramie-derived porous biochar for enhancing singlet oxygen generation and antibiotic degradation.

The Fe-N5 single-atom catalyst supported on porous carbon (Fe(S)-N-RBC) was fabricated from ramie fibers via molten salt-assisted pyrolysis. This method created a polar environment, yielding high-density Fe single atoms (4.5 wt%) and reconstructed pore structure. The Fe(S)-N-RBC/peroxydisulfate (PDS) system demonstrated efficient degradation of sulfamethoxazole (SMX) across an extensive pH range (3-9) and under high salinity, with excellent stability in continuous-flow reactors. Besides, it also exhibited excellent removal activity for diverse classes of antibiotics, confirming that this system had strong potential for practical application. Experimental results and density functional theory calculations revealed that molten salt-assisted pyrolysis modulated the coordination configuration of Fe-Nx sites and enhanced the electronic interaction between Fe-Nx and PDS, thus facilitated the PDS adsorption and lowered the energy barrier for generating singlet oxygen, which identified as the dominant reactive species. The reduced ecotoxicity of the degradation byproducts was confirmed by ecological structure activity relationship predictive modeling (ECOSAR) and phytotoxicity bioassays using Pisum sativum seedlings. This study provides key insights into an enhanced non-radical pathway facilitated by tailored Fe-N5 sites, offering a versatile molten-salt method for engineering single-atom catalysts for wastewater purification via advanced oxidation processes.