Metal-based ionic liquid-modified Mn/N co-doped biochar for tetracycline removal in environmental remediation: High-efficiency adsorption and interaction mechanisms

This work developed a novel Mn/N co-doped biochar (Mn/N-BC) using 1-methyl-3-methylimidazolium tetrachloromanganate ([Emim] 2 [MnCl 4 ]) as a modifier. The modification process increased the specific surface area (SSA) by 2.4 times and pore volume by 1.8 times, while simultaneously doping the biochar matrix with Mn and N, which provided additional adsorption sites and enhanced chemical reactivity. Adsorption experiments were conducted following pseudo-second-order kinetics and Langmuir isotherms, revealing a monolayer adsorption behavior. The maximum adsorption capacity of Mn/N-BC-3 for tetracycline (TC) was 2.8 times higher than that of unmodified biochar. Thermodynamic analysis indicated that the adsorption process was both spontaneous and endothermic. The adsorption mechanism involved multiple interactions, including pore-filling, hydrogen bonding, and π-π interactions. Density functional theory (DFT) calculations revealed that Mn and N doping significantly reduced the energy gap and increased adsorption energy, enabling stronger electronic interactions and enhancing the material’s affinity for TC. Regeneration experiments demonstrated that Mn/N-BC-3 retained 86 % of its initial TC adsorption capacity after five cycles, and leaching tests showed minimal Mn leaching. The material also exhibited excellent performance in real water, with a minimal reduction in TC adsorption in tap and river water. Furthermore, Mn/N-BC-3 showed effective adsorption of five different antibiotics. This study demonstrates that Mn/N-BC holds significant potential as an effective adsorbent for TC removal and demonstrates the versatility of metal ionic liquids in biochar modification. The findings provide valuable insights into developing advanced adsorbents for environmental remediation.