Biosorption of Silver using Metal-Imprinted Thiourea-Modified Glutaraldehyde-Crosslinked O-Carboxymethyl Chitosan Beads

Abstract

Chitosan, an abundant biopolymer obtained from deacetylation of chitin, has been proved to be a promising biosorbent for metal uptake. Grafting new functional groups on the chitosan backbone was also reported to be efficient in increasing either the sorption capacity or sorption selectivity for the target metal. In this study, silver-imprinted thiourea-modified glutaraldehyde-crosslinked O-carboxymethyl chitosan beads were prepared to selectively adsorb Ag (I) from a bimetallic aqueous solution. The biosorbent was synthesized by using prepared O-carboxymethyl chitosan beads to first absorb Ag (I) ion, then crosslinking with a polymeric Schiff’s base of thiourea/glutaraldehyde. To obtain the best performance sorbent, the degree of carboxymethylation substitution, and the amount of crosslinking agent used were studied. Results indicated the highest selective uptake capacity of Ag (I) occurred when a molar ratio of amino group of chitosan to carboxymethylation agent to crosslinking agent of 6:15:16 is used in the synthesis.

Batch sorption tests were carried out for isotherm and kinetic studies using the sorbent which provides the best selective uptake capacity of Ag (I). All isothermal and kinetic experiments were performed at 25 °C. The maximum uptake of Ag (I) was found to be 137.5 mgg^-1 at pH 5.0 with the initial concentration of Ag (I) being 1.75mmolL^-1. The sorbent demonstrated extremely good selectivity towards Ag (I) as equal mole of Cu (II) present in the solution was scarcely absorbed over a pH range from 1.0 to 6.0. The experiments also revealed that the biosorption process of Ag (I) fits well with a Langmuir model and Lagergren’s Pseudo-second-order kinetic.