Optimization of Biochar Adsorption Performance through Ball Milling and Nitrogen Doping: Mechanisms and Performance...

Antibiotic contamination in aquatic environments has become a critical environmental issue due to the persistence and ecological risks of tetracycline (TC). In this study, nitrogen-doped biochar (QN_7.5BC) was synthesized via ammonia-assisted ball milling to serve as an efficient adsorbent. The process incorporated pyrrolic-N, graphitic-N, and pyridinic-N groups, enhancing the surface polarity and providing abundant active sites. QN_7.5BC exhibited a high specific surface area of 206.88 m²/g and a total pore volume of 276 cm³/g. Batch adsorption experiments demonstrated a TC removal efficiency of 95.7%, which is more than twice that of pristine biochar. Spectroscopic analyses (FTIR, XPS, Raman) confirmed that nitrogen doping strengthened oxygen-containing functional groups (e.g., hydroxyl and carboxyl), promoted hydrogen bonding, π-π stacking, and electrostatic interactions, and improved structural stability, as reflected by a decrease in the Raman I _D/I _G ratio from 1.131 to 0.924. Even after TC adsorption, QN_7.5BC maintained a good structural integrity. These findings highlight the synergistic effects of nitrogen doping and pore structure optimization in enhancing TC adsorption, thereby demonstrating the potential of QN_7.5BC as a cost-effective and sustainable adsorbent for antibiotic wastewater treatment.