Modulation of ciprofloxacin adsorption conjugation effect by specific conformation of manganese-nitrogen co-doped biochar and its mechanistic study

Ciprofloxacin (CIP) is difficult to remove from the aqueous environment due to the stabilized it-electronic system in its naphthol structure. In this work, manganese-nitrogen co-modified biochar (Mn-N-BC) was skillfully prepared with tea waste as a carbon source, urea as a nitrogen source, and MnSO4 as a modifier. The manganesenitrogen co-doping not only enhances the it-electron donor capacity of the carbon structure by decreasing its electron cloud density and promotes the formation of a conjugate adsorption effect with the stable it-electron system (it-electron acceptor) in the CIP but also introduces additional oxygen-containing functional groups to enhance the formation of hydrogen bonding with the polar functional groups (O, F, and N) of the CIP. The maximum adsorption capacity (Qmax) of CIP is 121.42 mg/g, surpassing that of other adsorbents of the same category. In the different conformations of Mn-N-BC, the adsorption energy (Eads) of pyrrolic N exhibits the maximum absolute value of -2.07 eV, whereas the smallest energy gap between molecular orbitals is -0.27 eV. The tolerance of Mn-N-BC was evaluated in different cations/anions, humic acids, and actual water bodies. This study prepares efficient adsorbents for CIP removal and provides new insights into destabilizing the it-electron system for quinolone antibiotic removal by introducing specific conformations.