Biochar encapsulated metal nanoflowers for high efficient degradation of metronidazole via peroxymonosulfate activation

A three-dimensional (3D) flower-like zero-valent bimetallic shell/core iron/copper/biochar composite (NZVI/Cu⁰/BC) was synthesized for the purpose of removing antibiotic metronidazole (MNZ) through the activation of peroxymonosulfate (PMS). Under optimal conditions, complete removal of MNZ (10 mg/L) was achieved within 6 min. The study quantitatively investigated the contribution of different participants in the complex system, including carbon composites, Fe and Cu species, and radicals and nonradicals. Based on the characterization and analysis data, possible activation mechanisms were proposed, which involved the oxygenated functional groups of BC and the bimetallic structure feature of NZVI/Cu⁰ accelerating the generation of ¹O₂ and other oxidation species. Additionally, the synergistic effect of Cu-Fe-BC facilitated the redox cycle of Cu²⁺/Cu⁺ and Fe³⁺/Fe²⁺, thereby promoting radical in the NZVI/Cu⁰/BC-3/PMS system. Notably, NZVI/Cu⁰/BC-3 has the advantages of wide pH usable range as well as broad-spectrum adaptability towards various organic pollutant and various water environments. Density functional theory (DFT) results indicated that the adsorption energy of PMS onto NZVI/Cu⁰/BC was more negative compared to their individual adsorption energies, and the O-O bond in the structure of PMS molecules became weaker after adsorption, resulting in improved efficiency of PMS activation. Liquid chromatograph combined with mass spectrometry (LC-MS) measurement and DFT calculation suggested three main degradation pathways of MNZ, and the toxicities of their intermediates were evaluated.