Impact of process parameters on removal of Congo red by graphene oxide from aqueous solution

This study evaluated the performance of graphene oxide in the removal of Congo red (CR) dye from aqueous solution. The adsorbent, graphene oxide (GO), was prepared from graphite and was characterized using FTIR, SEM and XRD. Batch sorption studies were carried out to determine the effect of pH, contact time, initial concentration of CR and temperature on the adsorption of CR onto GO. Circumneutral pH was found to be favorable for the adsorption of CR onto GO. The equilibrium data fitted well with the Redlich-Peterson model and characterized by a Langmuir type isotherm. The kinetics of the adsorption data was analyzed using four kinetic models viz. pseudo-first-order, pseudo-second-order, Elovich model and intra-particle diffusion models. The results from the kinetic studies indicated that the rate of adsorption follows a pseudo-first-order with respect to the CR solution concentration and that in general the order of data fit is pseudo-first-order > pseudo-second-order > Elovich equation. The kinetic parameters obtained from the kinetic studies suggested that the adsorption process is film-diffusion-controlled. The results obtained from thermodynamic studies revealed that the adsorption process is endothermic in nature as well as the feasibility and spontaneity of CR adsorption onto GO. The values of ΔH and ΔS of the adsorption process were 8.19 kJ mol^-1 and 0.10 kJ mol^-1, respectively. The low value of ΔH (<40 kJ mol^-1) indicated that adsorption process occurs mainly through a physical means.