Adsorption of heavy metal cadmium(II) ions using chemically modified corncob: mechanism, kinetics, and thermodynamics

As one of the most produced agricultural wastes, corncob is considered for the removal of metal ions from aqueous solution as a low-cost biosorbent. This study reports the preparation of polyacrylamide grafted corncob and its excellent adsorptivity for Cd(II) ions in aqueous solution compared with crude corncobs. The adsorbents were characterized with scanning electron microscopy, BET, Fourier transform infrared, thermo gravimetric analysis, and swelling study. The higher Cd(II) uptake of polyacrylamide grafted corncob than crude corncob was due to increased surface area and number of functional groups (-NH2) that could complex with metal ions. Higher thermal stability and better swelling property in salt solution were achieved for corncobs after grafting modification. Experimental data greed with the Langmuir isotherm, and maximal adsorption capacities of polyacrylamide grafted and crude corncobs were 18.35 and 4.96mgg(-1), respectively. Kinetics study revealed that adsorption followed pseudo-second-order kinetics, and that chemical sorption was the rate-controlling step. Thermodynamic parameters (free energy G, enthalpy H and entropy S) showed that adsorption was a spontaneous endothermic process.