Engineered tea waste biochar for amoxicillin removal: Unraveling adsorption performance and mechanisms via integrated experimental and theoretical studies

• H 3 PO 4 treatment significantly enhanced AMX adsorption capacity of tea waste biochar. • H 3 PO 4 -modified waste biochar exhibited good reusability for AMX adsorption. • AMX adsorption on tea waste biochar was exothermic, and monolayer-dominated. • π–π stacking and surface complexation dominated AMX adsorption on tea waste biochar. The widespread misuse of antibiotics has resulted in significant contamination of water bodies, with amoxicillin (AMX) being among the most persistent and ecotoxic pollutants. Conventional treatment methods often suffer from low efficiency and potential secondary pollution. In this work, an eco-friendly adsorbent was developed from phosphoric acid-modified tea waste-derived biochar (P-TWB 750 ) for effective AMX removal. Characterization results confirm that phosphoric acid treatment modified the surface functional groups in P-TWB 750 . The optimized P-TWB 750 exhibited a high specific surface area of 989.01 m 2 /g and a porous structure, achieving 98.0 % removal of AMX via adsorption under optimal conditions (300 mg/L, 3.6 g/L, 15°C, pH 5.6). The adsorption process followed pseudo-second-order kinetics and the Langmuir isotherm, indicating a maximum capacity of 180.97 mg/g predominantly involving monolayer adsorption. Furthermore, the material demonstrated excellent reusability, maintaining over 80 % removal efficiency after four regeneration cycles. Combined characterization, experimental and theoretical calculation results suggest that the predominant mechanisms for the enhanced AMX adsorption by P-TWB 750 include surface function group interaction, π–π interactions, pore filling and diffusion, electrostatic interactions and thermodynamic driving forces. This work not only offers a sustainable and efficient strategy for remediating antibiotic-contaminated waters through circular economy principles, but also highlights the potential of waste-derived materials in advancing green water treatment technologies.