Hydrothermally synthesized carbon nanotubes mediated ZnO/Ag nanocomposites: Adsorption route to degrade ciprofloxacin

Ciprofloxacin (CIP), a widely used antibiotic from the fluoroquinolone family, significantly contributes to soil and water contamination by promoting antibiotic resistance genes and inhibiting microbial growth. Therefore, this study presents a low-cost hydrothermal method to synthesize CNTs doped with ZnO and hybridized with Ag-doped ZnO, effectively breaking down CIP. Crystallographic analysis revealed high purity of ZnO, Ag, and C in multiwalled carbon nanotubes. SEM images displayed flower-shaped ZnO nanorods and a dispersed, tube-like surface of CNTs. Peaks at 374.78 eV (Ag 3d 3/2 ) and 368.64 eV (Ag 3d 5/2 ), separated by 6.14 eV, indicated the doping of metallic Ag 0 from Ag + . Adsorption primarily drove the removal process, with an optimal dosage of 0.3 g/L for both nanocomposites. The removal efficiencies of ZnO-CNT and ZnO-Ag-CNT were 91.43% and 96.91% after 120 min of treatment at an optimum dose of 0.3 g/L. The CNT backbone assists in faster electron transport, whereas the Ag integration acts as electron traps that restrict the recombination of electron-hole pairs, thus increasing the removal efficiency. The R 2 values of 0.907 for ZnO-CNT and 0.972 for ZnO-Ag-CNT supported the pseudo-second-order kinetic model for removal. The kinetic data suggested multiple active sites influenced the reaction rate and removal. The rate constants (K obs ) demonstrated that ZnO-Ag-CNT catalysts accelerate adsorption, highlighting the effectiveness of metal doping in pollutant removal. Linearity in isotherm fitting favored the Langmuir model over the Freundlich model (R 2 >0.99).