N-doping biochar-supported Fe-Cu bimetallic catalyst for H₂O₂ activation to remove tetracycline: mechanism insight...

Tetracycline (TC) residues in aquatic ecosystems induce antibiotic resistance genes and pose ecological risks, which have garnered substantial scientific attention. In this study, FC@N-BC was synthesized via a sol-gel method followed by one-step pyrolysis, using a synergistic modification strategy that involved Fe-Cu bimetallic loading and nitrogen doping into biochar (BC). FC@N-BC significantly enhanced the activation ability of the BC-based catalyst for H₂O₂. Under natural pH conditions, the FC@N-BC/H₂O₂ system achieved 96.70 % removal of TC (100 mg/L), with degradation rates 34.67 and 19.63 times greater than those of H₂O₂ alone and the BC/H₂O₂ system, respectively. The presence of Cl^-, SO₄^2-, and visible light further enhanced TC removal. Fe and Cu were successfully loaded as nanoscale Fe₃O₄, Fe⁰, and Cu⁰ on the biochar. The high catalytic activity of FC@N-BC is attributed to its large specific surface area (S_BET = 234.46 m²/g), abundant pyridinic N, and efficient Fe(III)/Fe(II) and Cu(II)/Cu(I) redox cycles, which collectively promote continuous H₂O₂ activation and enhance the generation of reactive oxygen species (ROS). •OH was identified as the dominant ROS, with Cu(II) and Cu(I) species serving as the primary active sites. The system demonstrated an H₂O₂ utilization efficiency of 80.10 % and a TOC mineralization rate of 62.76 %, significantly reducing TC toxicity. After six cycles, FC@N-BC/H₂O₂ maintained a TC removal efficiency of 86.58 %. This study developed a highly efficient H₂O₂-activating material via multi-component modification of biochar, offering valuable insights for antibiotic removal and the application of biochar materials in the heterogeneous Fenton process.