Simultaneous adsorption and removal of copper and chlortetracycline hydrochloride in the wastewater using the bridge effect of BC-Cu-CTC with grape waste-based biochar: Synergistic effect and mechanism analysis.

The combined pollution of heavy metals and antibiotics continues to threaten the safety of water bodies. Adsorption is an effective approach for removing the combined pollution of metals and antibiotics. Low-cost grape stalk biochar (SBC) and grape leaf biochar (LBC) were prepared through direct pyrolysis of grape waste. In the binary system (20 mg/L Cu2++10 mg/L CTC), the adsorption capacities of SBC for Cu2+ and CTC were 57.46 and 23.54 mg/g, respectively, while those of LBC were 56.71 and 20.82 mg/g, respectively. Compared with single adsorption, the removal rate of Cu2+ increased by 16.49% and 25.36% for SBC and LBC, respectively, the removal rates of CTC increased 26.22% and 41.03% for SBC and LBC, respectively. The adsorption removal process of Cu2+ and CTC followed Pseudo-Second-Order kinetics (PSO), primarily involved chemical adsorption. The adsorption isotherms could be described using a multi-isotherm model, indicating that the removal of Cu2+ and CTC involved multiple mechanisms. In addition to pore filling and electrostatic attraction, the adsorption of Cu2+ was primarily attributed to ion exchange and complexation, whereas the adsorption of CTC was mainly due to hydrogen bonding and π-π electron donor-acceptor (EDA) interactions. Density functional theory (DFT) calculations indicated that after the adsorption of Cu2+, the electron cloud density on the surface of biochar decreased, and CTC transitions from an electron acceptor to an electron donor, confirming that Cu2+ was a bridging molecule in the reaction. The results from the adsorption energy and HOMO-LUMO energy gap indicated that coexistence enhanced the adsorption energy and reduced the energy gap, regulating electronic interactions and achieving a synergistic adsorption effect. These findings provided theoretical basis and data support for the synergistic adsorption and immobilization of heavy metals and antibiotics.