Engineering high-performance magnetic biochar for efficient tetracycline capture

Upcycling Chinese herbal medicine residues (CHMRs) into functional biochar adsorbents for treating antibiotic-contaminated wastewater aligns with the development philosophy of “using waste to reduce waste.” To address the challenges of easy agglomeration and limited pore development in the single-step modification of iron oxides, a novel two-step modification strategy, termed “activation (K 2 CO 3 )–magnetization (K 2 FeO 4 )” was developed. The initial K 2 CO 3 activation pre-constructs a mesoporous carbon framework as a spatial template for K 2 FeO 4 loading; subsequent pyrolytic reduction achieves “spatial confinement” and high dispersion of iron nanoparticles while introducing a large number of oxygen-containing functional groups. The magnetic biochar (KFeBC) synthesized through this method exhibited a specific surface area (S BET ) of 915.87 m 2 /g and a total pore volume (V total ) of 0.745 cm 3 /g. Systematic batch adsorption investigations indicated that the interaction between KFeBC and tetracycline (TC) adhered to pseudo-second-order (PSO) kinetics and the Freundlich isotherm model. Notably, at 318 K, KFeBC achieved a maximum adsorption capacity of 1060.36 mg/g. Continuous fixed-bed column experiments (C 0 = 25 mg/L, Z = 1 cm, and Q = 2 mL/min) demonstrated a robust dynamic adsorption capacity of 284.55 mg/g. Mechanistic elucidation quantitatively decoupled the primary driving forces, revealing contributions from pore filling (33.8%), surface complexation (27.4%), π-π interactions (21.0%), and hydrogen bonding (13.9%). Overall, this study provides an economical and efficient pathway for the high-value utilization of CHMRs, establishes a robust theoretical framework for engineering high-performance biochars, and provides practical technical solutions for global antibiotic remediation.