Equilibrium, kinetic and thermodynamic studies on adsorption of cationic dyes from aqueous solutions using graphene oxide

The adsorption of cationic dyes Basic Yellow 28 (BY28) and Basic Red 46 (BR46) from an aqueous solution by graphene oxide (GO) as adsorbent is presented. Graphene oxide is prepared using a modified Hummers’ method and characterized by Fourier Transform-Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Atomic Force Microscopy (AFM), Raman spectroscopy, Transmission Electron Microscopy (TEM) and zeta potential measurements. Adsorption properties of cationic dyes using GO were studied in different dye concentrations (10–50 mg L−1), pH of the solutions (3.0–11.0), and temperature range of 20–60 °C. The Langmuir and Freundlich isotherm models were applied to fit the adsorption data. Equilibrium data fitted very well with the Langmuir isotherm model. The maximum monolayer adsorption capacity of BY28 and BR46 onto GO was 68.5 and 76.9 mg g−1, respectively. The experimental kinetics data were analyzed using pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models. The kinetic studies showed that the adsorption data followed the pseudo-second-order kinetics model. In addition, various thermodynamic parameters, such as the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were calculated and it was revealed that the adsorption of BY28 and BR46 was spontaneous and endothermic.