Studies on Adsorption of Some Organic Dyes from Aqueous Solution onto Graphene Nanosheets

Graphene, a new member of the carbon family, was used as an adsorbent due to its exceptional capability to remove Rhodamine B (RB) and Malachite Green (MG), two organic dyes, from aqueous solutions. Adsorption kinetics of RB and MG onto graphene and adsorption capacity of the adsorbent were studied. Also the effects of parameters, including pH, contact time, temperature, and adsorbent dosage were studied. The adsorption process was followed using UV-visible spectroscopy. The isotherm analysis indicated that Freundlich and Langmuir isotherms are suitable for RB and MG, respectively. Pseudo-first- and pseudo-second-order models were considered to evaluate rate parameters. The kinetic experimental results fitted well the pseudo-second-order model for the two dyes, with correlation coefficients being greater than 0.99. Thermodynamic studies indicated that the adsorption processes is spontaneous for both the dyes, and exothermic for RB and endothermic for MG.