AbstractThe synergistic and antagonistic effects that are involved in the adsorption of metronidazole (MNZ) and ciprofloxacin (CIP) as single and binary mixtures were investigated. First, a chitosan-modified graphene oxide (CS–GO) adsorbent was synthesized (as beads) and characterized using Fourier-transform infrared spectroscopy (FTIR), Bruaneur–Emmett–Teller (BET), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analysis. The FTIR graph showed amino bond formation between a carbonyl with an amino (NH2) group and intermolecular hydrogen (H) bond between the hydroxyl (OH) and carboxyl (COOH) with the NH2 group of GO and CS, respectively. In addition, the SEM and XRD diagrams revealed a good attachment between CS and GO. The kinetic sorption experiments revealed that adsorption followed pseudo second-order with a higher rate constant for CIP than MNZ. In a single solute system, adsorption followed the multilayer Langmuir isotherm with maximum adsorption capacities of 29.76 and 102 mg/g for MNZ and CIP, respectively. In the binary mixture, MNZ and CIP showed antagonistic effects with a respective decrease in adsorption capacities to 13.15 and 4.3 mg/g, respectively. The major interactions inferred were π–π electron donor–acceptor (EDA), H bond, and hydrophobic interactions for both antibiotics along with electrostatic and cation–π interactions for CIP. In addition, the adsorbent showed good disinfection capability for secondary treated effluents, and the disinfection potential was further increased by the addition of a small amount of silver (Ag). The CS–GO showed good performance and stability in the removal of CIP and MNZ in single and binary mixture experiments. However, the repeated use of the adsorbent showed a decrease in the removal of CIP and MNZ, which requires further investigation.

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