Comparative study of peroxymonosulfate activation with H₂O₂ activation by Cu-N doped biochar derived from peach gum...

The design and development of efficient biochar catalysts is an urgent need for the removal of toxic contaminants from water bodies. Peach gum (PG) is a natural colloid featuring a heteropolysaccharide macromolecule structure. Herein, Cu²⁺ was anchored to the macromolecule of peach gum with dicyandiamide serving as the auxiliary ligand. Then, copper-nitrogen codoped peach gum biochar (Cu-N-PGC) was successfully prepared by the pyrolysis of the Cu²⁺/dicyandiamide modified peach gum precursor. Structural characterization demonstrated that CuO nanoparticles, pyridinic-N, and pyrrolic-N structures have been successfully constructed and uniformly doped into the graphitic structure of peach gum biochar. The mesoporous structure was fabricated in Cu-N-PGC composites by using NH₄HCO₃ as pore-making agent, and the adsorption of tetracycline (TC) on Cu-N-PGC-350 could be described by Langmuir isotherm model and pseudo-second-order kinetic model. The Cu-N-PGC biochar exhibited outstanding activation performance for peroxymonosulfate (PMS) and hydrogen peroxide (H₂O₂) in the removal of TC. Cu-N-PGC-350 showed the highest catalytic activity by activating PMS in the darkness, achieving a removal efficiency of 99.8 % for TC within 15 min. The rate constant obtained by PMS activation (0.38 min^-1) was 4.47 times higher than that by H₂O₂ activation (0.085 min^-1), suggesting Cu-N-PGC-350/PMS system was more efficient than the Cu-N-PGC-350/H₂O₂ system. The catalytic mechanism was studied through trapping experiments, EPR tests, and molecular electrostatic potential calculation, which reveals that ¹O₂ and SO₄·^- are the primary reactive species in the Cu-N-PGC-350/PMS system, while •OH is the main reactive radical generated in the Cu-N-PGC-350/H₂O₂ system. The degradation pathways of TC were proposed through the analysis of liquid chromatography-mass spectrometry (LC-MS), and the ecotoxicology of TC before and after degradation was evaluated by the TEST toxicity assessment and the rice seeds germination tests. This work presents an effective approach for the preparation of functional biochar with tree gum, thereby technically addressing the issue of uneven doping of metal-N active sites in biochar.