Adsorption and kinetic study of Reactive Red 2 dye onto graphene oxides and graphene quantum dots

Abstract

The increase of the water pollution has led to the search of new methods and materials for its remediation. In recent years, different carbon nanomaterials have gained importance in the removal of dyes from water. In this research was investigated the adsorption of Reactive Red 2 (RR2) dye onto different graphene oxides and graphene oxide quantum dots at pH values of 2 and 5. The graphene oxide samples were obtained modifying the amount of KMnO4 used and replacing the magnetic stirring by ultrasonic bath in the oxidation reaction. In order to know the surface and structural properties of carbon nanomaterials, these were analyzed by infrared, Raman and energy dispersive X-ray spectroscopies, transmission electron microscopy and field emission scanning electron microscopy, nitrogen-adsorption and through potentiometric titrations was obtained the point of zero charge. The decrease in the amount of KMnO4 used in the Hummers´ reaction induced an increase in the oxygen content of graphene oxide. All carbon nanomaterials presented a high affinity by the RR2 dye at pH = 2, however graphene quantum dots showed the best performance. The removal of RR2 is dependent of the pH, surface area, oxygenated groups and the dimensionality of the carbon nanomaterials. The experimental data are analyzed using pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion models to describe the adsorption kinetics from RR2 in aqueous solutions. Based on the highest coefficient of determination values and the lowest standard deviation values, the experimental kinetic data are better adjusted by the Elovich's equation. The adsorption behavior is studied according to the RE values of the dimensionless Elovich's equation.