Understanding the adsorption property of graphene-oxide with different degrees of oxidation levels

Abstract

In this paper, we report the systematic removal of synthetic dye compound from aqueous solution using graphene-oxide (GO) nanostructures as an adsorbent. The various levels of oxidized GO were used in this study and their results were systematically compared. Highly oxidized GO revealed superior adsorption capacity than the GO with lower degree of oxidization. In highly oxidized GO, the presence of more hydrophilic (sp3 hybridization) functional groups enhanced the dye adsorption. At ambient atmospheric condition, the adsorption rates were increased with respect to the oxidation rate of GO which is due to its increase in negative charge molecules in the hydrophilic functional groups. The adsorption property of GO was investigated by gradually varying the pH of solution, temperature and reaction time. Thermodynamic parameters were also calculated using Van't Hoff plot. The value of Gibbs free energy was found to be negative as the adsorption reaction was spontaneous. The positive value of ΔH indicates that the adsorption process of all GO samples is purely based on an endothermic process. The adsorbent was characterized by using XRD and the functional groups in GO were characterized by using an FTIR spectrometer. Our results show a very simple and cost effective procedure for removing the toxic and carcinogenic dyes from the waste water and their applications.