Ammonium persulfate-triggered modified chitosan biochar for co-adsorption of Cr(VI) and tetracycline antibiotics: Behavior and mechanisms.

Antibiotic and heavy metal contamination of soil and groundwater together constitute a serious environmental issue. This study developed APS@CHI-1:3, a high-performance biochar derived from chitosan modified with ammonium persulfate (APS) and acetic acid, through a two-step carbonization process: hydrothermal pre‑carbonization at 180 °C for 6 h, followed by K₂CO₃ activation (1,3 mass ratio) at 800 °C for 2 h under N₂. The resulting material exhibited a high specific surface area (1656 m2/g) and abundant surface functional groups. The optimized adsorbent exhibited exceptional adsorption capacities of 851.5 mg/g for tetracycline (TET) and 777.4 mg/g for chlortetracycline (CTC) at 308 K, surpassing most reported biochars. In binary systems containing Cr(VI), APS@CHI-1:3 achieved 60.54 % Cr(VI) removal (48.45 mg/g) alongside simultaneous TET/CTC adsorption, demonstrating robust performance under competitive conditions. Mechanistic studies revealed that the adsorption was governed by electrostatic attraction, Lewis acid-base interactions, hydrogen bonding, and π-π interactions. The material maintained >92 % adsorption efficiency after 5 regeneration cycles, highlighting its reusability. These findings highlight its potential application in remediating complex wastewater systems co-contaminated by heavy metals and antibiotics.