A Novel N Self-Doped Porous Biochar Synthesized by KHCO₃-Activated Chicken Feather for the Remediation of Tetracycline-Contaminated Water and Soil

N self-doped porous biochars (KBCs) were synthesized through high-temperature carbonization and KHCO₃ activation using chicken feathers as biomass. Subsequently, it was employed for the remediation of tetracycline hydrochloride (TC)-contaminated water and soil. The properties of KBCs were analyzed by various characterization techniques. The results verified that KBC_800-2 exhibited outstanding specific surface area (1648.89 m² g⁻¹) and pore volume (0.806 cm³ g⁻¹). The maximum adsorption capacity of KBC_800-2 for TC was 147.8 mg g⁻¹, which was superior to that of raw biochar (15.5 mg g⁻¹). The results of pseudo-second-order and Freundlich indicated that the process was dominated by chemisorption. Moreover, the adsorption capacity of KBC_800-2 was stable over a wide pH range of 3–12 and high coexisting ionic strength. The consequences proved that the enhancement of pore filling effect and π-π electron interactions between TC and N self-doped adsorbent were the predominant driving forces to improve the adsorption efficiency of TC. Notably, compared to T50 (soil and 50 mg kg⁻¹ TC), the properties of organic carbon, total nitrogen, and sucrase, urease, and catalase activities in TKBC_800-2 (soil, 50 mg kg⁻¹ TC, and 2% KBC_800-2) were increased by 108.57%, 4.98%, 886.08%, 89.52%, and 78.08% respectively. KBC_800-2 as a low-cost and highly effective adsorbent for antibiotic pollution has enormous application potential.