Graphene nanosheets as efficient adsorbent for an azo dye removal: kinetic and thermodynamic studies

Abstract

Graphene nanosheets were synthesized by a cost effective, simple, and environmentally friendly procedure via burning Mg ribbons in dry ice. The graphene nanosheets were characterized by seven methods including X-ray diffraction, transmission electron microscopy (TEM) and high-resolution TEM, scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and N2 adsorption–desorption technique (BET). The BET analysis confirmed that graphene nanosheets with the average pore diameter of 6.28 nm can be considered as a good adsorbent. The next step was to investigate the potential of graphene nanosheets for adsorption of an azo dye, Reactive Black 5 (RB5). The influence of different parameters including adsorbent dosage, pH, temperature, dye concentration, and ionic strength on the dye removal efficiency was studied. The experimental data were fitted well with the pseudo-second-order kinetic model (R 2 = 0.997). The activation energy of 25.80 kJ mol−1 revealed the physisorption of RB5 on graphene. The adsorption isotherm was described well by Freundlich isotherm. The high value of Freundlich constant (191.9 mg1−1/n L1/n g−1) shows the high capacity of graphene for the RB5 adsorption from aqueous solutions. The thermodynamic parameters confirmed that the RB5 adsorption on graphene surface was spontaneous and endothermic. Some significant features of using graphene as an adsorbent for RB5 removal are the fast dye removal process, the low required amount of graphene, and the frequent usage of graphene with no change in its efficiency.