Synthesis and characterization of polyacrylamide-grafted coconut coir pith having carboxylate functional group and adsorption ability for heavy metal ions

The present investigation was undertaken to evaluate the effectiveness of a new adsorbent prepared from coconut coir pith (CP), a coir industry-based lignocellulosic residue in removing metal ions from aqueous solutions. The adsorbent (PGCP-COOH) having a carboxylate functional group at the chain end was prepared by grafting polyacrylamide onto CP using potassium peroxydisulphate as an initiator and in the presence of N,N'-methylenebisacrylamide as a crosslinking agent. The adsorbent was characterized by infrared (IR) spectroscopy, thermogravimetry (TG), X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM), and potentiometric titration. The adsorbent exhibits very high adsorption potential for the removal of Pb(II), Hg(II), and Cd(II) ions from aqueous solutions. The optimum pH range for metal ion removal was found to be 6.0-8.0. The adsorption process follows a pseudo-second-order kinetic model. The adsorption capacities for Hg(II), Pb(II), and Cd(II) calculated using the Langmuir isotherm equation were 254.52, 189.49, and 63.72 mg g(-1), respectively. Adsorption isotherm experiments were also conducted for comparison with a commercial carboxylate form cation exchanger. Different industry wastewater samples were treated by the PGCP-COOH to demonstrate its efficiency in removing heavy metals from wastewater. The reusability of the PGCP-COOH was also demonstrated using 0.2M HCl (c) 2007 Wiley Periodicals, Inc.