Efficient Sorption of Cu 2+ by Composite Chelating Sorbents Based on Potato Starch-graf t-Polyamidoxime Embedded in Chitosan Beads Ecaterina Stela Dragan,* Diana Felicia Apopei Loghin, and Ana Irina Cocarta “Petru Poni” Institute of Macromolecular Chemistry, Grigore Ghica Voda Alley 41 A, Iasi 700487, Romania ABSTRACT: Ionic composites based on cross-linked chitosan (CS) as matrix and poly(amidoxime) grafted on potato starch (AOX) as entrapped chelating resin were prepared as beads, for the first time in this work, by two strategies: (1) thorough mixing of previously prepared AOX in the CS solution followed by the bead formation and (2) thorough mixing of the potato starch-g- poly(acrylonitrile) (PS-g-PAN) copolymer in the initial CS solution, followed by bead formation, the amidoximation of the nitrile groups taking place inside the beads. Ionotropic gelation in tripolyphosphate was used to obtain the composite beads, and in situ covalent cross-linking by epichlorohydrin was carried out to stabilize the beads in the acidic pH range. Fourier transform infrared spectroscopy and the swelling ratio values in the acidic pH range confirmed the influence of the synthesis strategy on the structure of the CS/ AOX composites. Scanning electron microscopy was employed to reveal the morphology of the novel composites, both before and after their loading with Cu 2+ . The binding capacity of Cu 2+ ions as a function of sorbent composition, synthesis strategy, pH, sorbent dose, contact time, initial concentration of Cu 2+ , and temperature was examined in batch mode. The main difference between the composites prepared with the two strategies consisted of the higher sorption capacity and the much faster settlement of the equilibrium sorption for the composite prepared by the in situ amidoximation of PS-g-PAN. The Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, and Sips isotherms were applied to fit the sorption equilibrium data. The maximum equilibrium sorption capacity, q m , evaluated by the Langmuir model at 25 °C was 133.15 mg Cu 2+ /g for the CS/AOX composite beads prepared with the first strategy and 238.14 mg Cu 2+ /g for the CS/AOX composite beads prepared with the second strategy, at the same AOX content. The pseudo-second order kinetic model well fitted the sorption kinetics data, supporting chemisorption as the mechanism of interaction between the chelating composites and the Cu 2+ ions. The CS/AOX composite sorbents could be reused up to five sorption/desorption cycles with no significant decrease in Cu 2+ sorption capacity. KEYWORDS: chitosan, composite, potato starch, poly(amidoxime), copper 1. INTRODUCTION Pollution of water and soil by heavy metal ions is considered extremely hazardous to the environment because of their nonbiodegradability, high toxicity, and carcinogenic effect. Inadequately treated effluents transport heavy metals to water bodies, where they accumulate in aquatic organisms and are further transferred to the human body through the food chain. Among the conventional technologies used for the heavy metal removal, such as chemical treatment, evaporation, electrolysis, membrane separation, ion exchange, separation/enrichment by sorption, and biological processes, adsorption is considered superior to the other techniques in terms of low costs and operation. Other advantages of adsorption include the flexibility in the selection of the adequate sorbent, and the possibility of enriching the trace metal amounts. 1,2 The use of sorbents derived from polysaccharides, as a more cost-effective alternative to the existing sorbents such as activated carbon and synthetic ion exchangers, has lately attracted considerable interest. 3-13 Chitosan (CS) is a linear cationic semisynthetic polysaccharide, composed of β-(1-4)-2- amino-2-deoxy-D-glucopyranose and β-(1-4)-2-acetamido-2- deoxy-D-glucopyranose units, obtained by deacetylation of its parent natural polymer chitin. Among biopolymers, CS has a special position due to its outstanding properties such as biocompatibility, antibacterial activity, high mechanical strength, film forming properties, which recommend it for numerous biomedical applications. 14 Moreover, the abundance of hydroxyl, acetamido and amino functional groups in CS generates hydrophilicity and excellent chelating properties for heavy metal ions. 3-10 On the other hand, sorbents containing amidoxime functional groups show a high tendency of chelation with transition and heavy metal ions, such as UO 2 2+ , Cu 2+ , Cd 2+ , Fe 3+ , As 3+ , and Zn 2+ in aqueous solutions. 15-24 It has been observed that sorbents containing both amidoxime groups and other hydrophilic groups, such as hydroxyl, carboxyl, and amide, have a much higher sorption capacity for metal ions. Therefore, some sorbents based on polysaccharides grafted with poly(amidoxime), generated by the reaction between Received: May 15, 2014 Accepted: September 5, 2014 Published: September 5, 2014 Research Article www.acsami.org © 2014 American Chemical Society 16577 dx.doi.org/10.1021/am504480q | ACS Appl. Mater. Interfaces 2014, 6, 16577-16592