Defect-driven bifunctional Cu/N co-doped biochar for synchronized adsorption and instant catalysis in organic pollutant degradation

As a commonly used antibiotic in healthcare and livestock production, tetracycline (TC) remains in water bodies and poses ecological and health risks, making its efficient removal from wastewater essential. A copper (Cu) and nitrogen (N) co-doped biochar (BC) catalyst (denoted as Cu-N@KBC) was synthesized, exhibiting low energy consumption, excellent adsorption capacity, and superior catalytic performance. Cu-N@KBC achieved 35.2 % TC removal within 20 min, with the solid-liquid distribution coefficient (K_d) of 4.541 L g⁻¹, owing to its well-developed pore structure and abundant defect sites. N doping into the sp²-hybridized carbon network, synergistically coupled with uniform Cu loading, induced the formation of oxygen vacancies and surface defects, thereby creating additional active sites for TC adsorption. A maximum TC degradation of 96.5 % was achieved within 60 min under the optimized conditions. The combined incorporation of Cu and N elevated the graphitization degree (I_D/I_G = 0.93), optimizing electron transfer and facilitating ≡ Cu²⁺-O-O-SO₃ configuration. This further accelerated the Cu⁺/Cu²⁺ redox cycle and the generation of reactive oxygen species (ROS) (•OH, SO₄^•−, O₂^•−, ¹O₂, and Cu^III=O). Additionally, the Cu-N@KBC/peroxymonosulfate (PMS) system demonstrated excellent stability, universality, and resistance to interference. Notably, its integration with membrane technology demonstrated the potential of the Cu-N@KBC-cellulose acetate membrane for practical wastewater treatment applications. This study offered a fresh perspective on the adsorption mechanism and the ¹O₂-dominant non-radical degradation pathway of Cu-N@KBC/PMS/TC system.