Adsorption of Ciprofloxacin on Graphene Oxide-Based Adsorbents: Synthesis, Characterization and DFT Calculations

In this article, the synthesis of graphene oxide from coal or coke and a composite graphene oxide-geopolymer were carried out to produce adsorbents applied to Ciprofloxacin (CIP) removal from water in a laboratory scale. The characterization analyzes of the adsorbent were performed by Thermogravimetric Analysis (TGA), Zeta Potential (ZP), Particle Size Distribution (PSD), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Gun Scanning Electron Microscopy (FEG/EDS), and RAMAN spectroscopy. Multilayer graphene oxide was identified after coal or coke thermal treatment and ultrasound exfoliation followed by ozone oxidation of the solid surface. A composite produced using phosphate mining residues and graphene oxide incorporation (22 wt%) showed the highest adsorption capacity. Affinity tests showed removal rates for CIP ranging from 15% to 55%. Kinetic studies indicated that the equilibrium time varied between 100 min and 120 min for three different initial CIP concentrations. With regard to the kinetic study, the pseudo-first order model better described the kinetics at the concentration of 0.05 mmol L^-1, while the pseudo-second order model better described the kinetics at concentrations of 0.1 mmol L^-1 and 0.2 mmol L^-1. The studies on adsorption equilibrium showed that the Langmuir model provided the most accurate fit to the experimental data. The maximum adsorption capacity was found at 45 °C and it was of 0.24 mmol g^-1. The possible mechanisms of adsorption are related to electrostatic interactions and covalent bonds.