Assessing Zn₁₂O₁₂ nanocage for the elimination of ciprofloxacin from drinking water using DFT simulations

According to the biochemical theory, the presence of pollutants such as antibiotics is a worldwide issue since they foster antibiotic resistance. A detailed DFT analysis was carried out to examine the adsorption capabilities of the Zn₁₂O₁₂ nanocage for ciprofloxacin (CIP). Five optimal structures of Zn₁₂O₁₂-CIP complexes were identified, designated as CMP-1, CMP-2, CMP-3, CMP-4, and CMP-5. CMP-3 shows the most favorable adsorption with E_ads values of 48.99 kcal/mol, representing the strongest interaction without any structural deformation of the nanocage. The interaction occurs through the bonding of the F and O atoms of CIP with the Zn and O atoms of the nanocage, respectively. FMO indicated a reduction in the bandgap for the Zn₁₂O₁₂-CIP complexes, making the complexes more reactive and suggesting the favorable adsorption characteristics of the nanocage for the drug. The NBO analysis revealed that the CMP-3 complex had the highest charge transfer of 0.139 e with the bond distances of 1.92 Å and 1.25 Å, respectively. The presence of covalent and weak electrostatic interactions between the nanocage and CIP molecules was confirmed by QTAIM, NCI, and RDG analyses. The thermodynamic assessment showed that the adsorption process is spontaneous. The extremely high adsorption energy values limit the complete desorption process and reduce the regeneration ability of the Zn₁₂O₁₂ nanocage. Overall, the nanocage has proven theoretically to be a potential candidate for environmental remediation applications.