Tetracycline adsorption on nitrogen-doped furfural residue biochar: Kinetics, thermodynamics and mechanism analysis

Converting biomass waste into high-performance adsorbents is crucial for environmental remediation. In this study, a novel nitrogen-doped porous biochar (FRLB-K-N) with an ultra-high specific surface area (3463.87 m 2 /g) was synthesized from furfural residue lignin. FRLB-K-N exhibited an extremely high adsorption capacity (q e ) of 2242 ± 7.8 mg/g for tetracycline (TC). The results indicate that the abundant ordered graphite structure of the lignin-based adsorbent enhances its adsorption capacity for organic pollutants through conjugated aromatic interactions. Following lignin purification, the q e increases by 51 ± 8.9 %. The synergistic effect of melamine and KOH on the etching of the carbon skeleton not only enhances the adsorption capacity, but also optimizes the pore structure of the porous carbon, thereby improving the kinetic performance. The coexisting metal ions inhibit the adsorption of TC on FRLB-K-N by competitively adsorbing and occupying the active sites. The FRLB-K-N exhibited remarkable adsorption capacity for TC across a broad pH range (pH=2–10), attributed to its ultra-high specific surface area, abundant surface oxygen groups (including C O, -OH etc.) and ordered aromatic structure. The adsorption mechanism belongs to monolayer chemisorption, mainly maintained by electrostatic interaction, hydrogen bonding, π-π stacking, and pore filling to maintain its high adsorption performance in real aqueous environments. Notably, FRLB-K-N exhibits excellent stability and recyclability. Its adsorption capacity remains nearly unchanged after five recycles via simple desorption, indicating its great potential as a robust and recyclable adsorbent for antibiotic removal in practical applications.