Kinetics of the adsorption of Pb(II) ions from aqueous solutions by graphene oxide and thiol functionalized graphene oxide

Adsorption capacity of Pb^{2 +} on graphene oxide and thiol functionalized graphene oxide was well investigated and illustrated in the present work. Variable cysteamine concentrations i.e., 60, 80 and 100 mg were used as functionalizing agent for conversion of graphene oxide to thiol functionalized graphene oxide. The surface of graphene oxide (GO) was functionalized by the use of 60 mg of cysteamine (GO-SH1), by 80 mg of cysteamine (GO-SH2) and by 100 mg of cysteamine (GO-SH3), respectively. The prepared adsorbents were characterized using Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The impact of several influential parameters such as adsorption time, pH, temperature and cysteamine concentrations on Pb^{2 +} adsorption was well elucidated and optimized. The optimized values of adsorbent dose, initial concentration of Pb^{2 +}, contact time, and pH were found to be 20 mg, 25 mg/L, 60 min and 6 respectively at a temperature of 298 K. The kinetic experimental data for GO surface was well fitted and found to be in good agreement with type (II) of pseudo-second-order model, and for GO-SH1, GO-SH2, and GO-SH3 the experimental data was in good agreement with pseudo first-order model, type (IV) of pseudo-second-order model and type (II) of pseudo-second-order model respectively. Results revealed that the adsorption capacity of Pb^{2 +} on to the developed adsorbent increases with the increase in temperature, hence this process was endothermic in nature.