Synergistic and antagonistic adsorption mechanisms of copper(II) and cefazolin onto bio-based chitosan/humic composite: A combined experimental and theoretical study

In this study, a bio-based chitosan adsorbent modified by humic was synthesized. The adsorbent exhibited amphoteric adsorption properties and had a higher adsorption capacity for Cu(II) and cefazolin (CEF) than its precursors. The impacts of pH on the speciation and adsorption of Cu(II) and CEF were analyzed. The synergistic and antagonistic adsorption in Cu(II)/CEF co-existing system were systematically investigated. The adsorption amount of CEF significantly increased by 84 %, owing to the bridge effect of Cu(II). While the uptake of Cu(II) decreased by 29 % at CEF concentration of 0.3 mmol/L, due to the formation of organic ligand complex between Cu(II) and CEF with low affinity to the adsorbent. The adsorption mechanisms of Cu(II) and CEF were analyzed by XPS and Density functional theory (DFT). Through DFT calculations, the interaction configurations of Cu(II) and CEF on adsorbent as well as Cu(II)-CEF complexes were configurated. The possible Cu(II)-CEF complexes configuration were optimized, and the complex configuration (Cu-N2/O1/O2) was the most stable combination structure with the lowest binding energy (−2066.61 kJ/mol). Interaction region indicator (IRI) model further elucidated the chemical and weak interactions between CEF and Cu(II) in coexisting system. In addition, the influence of common inorganic electrolytes on the adsorption of Cu(II) and CEF was assessed. The adsorbent could be stably recycled for five cycles with little loss, indicating the potential application in the treatment of combined pollution. This study proposed more insights into the interactions of heavy metal ions and antibiotics in the coexistence system onto the adsorbents containing amine and carboxyl groups. [Display omitted] •In the co-presence of Cu(II), the adsorption of CEF increased by 84 %.•Cu(II)-CEF ligand complexes resulted in the synergistic and antagonistic adsorption.•Interaction region indicator model elucidated the chemical and weak interactions.•The configurations of Cu(II) and CEF onto amine-containing adsorbent were analyzed.