Modified polyacrylamide hydrogels and their application in removal of heavy metal ions Hasine Kas ¸go ¨z * , Saadet O ¨ zgu ¨mu ¨s ¸, Murat Orbay Department of Chemical Engineering, Faculty of Engineering, Istanbul University, Avcılar Campus, 34320 Istanbul, Turkey Received 2 October 2002; received in revised form 3 January 2003; accepted 15 January 2003 Abstract Modified crosslinked polyacrylamides having different functional groups were prepared by Mannich reaction using different amine compounds such as ethylenediamine (EDA), diethylenetriamine (DETA) and triethylenetetramine (TETA) and sulfomethylation reaction. Products were characterized by determination of their basic group content (BGC), hydroxymethyl group content (HMG), equilibrium degree of swelling (EDS) and FT-IR spectra. For Mannich reactions, BGC and EDS changed with amount of employed amine compounds, reaction time and temperature. Sulfomethylation reactions gave products with high BGC and very high EDS. FT-IR spectroscopic analysis confirmed that a parallel hydrolysis reaction occurred along with the expected modification reactions. The products were used for removal of Cu(II), Cd(II) and Pb(II) ion under competitive and non-competitive conditions at different pH. The metal ion removal capacities changed depending their BGC and EDS. While the Mannich products were selective towards Cu(II) ion, the sulfomethylation products were highly selective to Pb(II) ions. The polymers were used several times by regeneration without loss of adsorption capacity and changing of selectivity properties. q 2003 Elsevier Science Ltd. All rights reserved. Keywords: Modified polyacrylamide hydrogel; Heavy metal ion removal; Competitive adsorption 1. Introduction Modified polymers can be obtained by copolymerization of monomers with different functional groups or by post- modification of polymerised products. The second option is generally preferred to prepare materials which are difficult to obtain by direct polymerisation of the corresponding monomers. An example is polyacrylamide with amide groups which are stable in the intermediate (or neutral) pH range that can be converted to –COOH groups by hydrolysis, to –OH containing groups by the reacting with formaldehyde, to –NH 2 groups by the Hofmann reaction and to –SO 3 containing groups by the sulfomethylation reaction [1–3]. Crosslinked hydrophilic polymers capable of imbibing large volumes of water have found widespread applications in bioengineering, biomedicine, food industry and water purification and separation processes [4]. Modified poly- acrylamide hydrogels find various commercial applications such as recovery of secondary oil, stabilization of mineral sedimentation, purification of wastewater and metal extrac- tion [5,6]. In recent years, it was determined that crosslinked polymeric materials having functional groups such as carboxylic acid, amine, hydroxyl and sulfonic acid groups could be used as complexing agents for the removal of metal ions from aqueous solutions. Main advantages of such materials are easy loading and, in most cases, stripping of cations with simple chemicals, reusability and the possi- bility of semi-continuous operation. Ionic polyacrylamide gels have been used for this purpose [4]. In previous works, modified polyacrylamides have been obtained from linear polyacrylamides by various modifi- cation reactions such as Mannich [7], Hofmann [8,9] or by copolymerization of different functional monomers, such as dimethylaminoethyl methacrylate, 2-acrylamidopropane sulfonic acid, 3-acrylamido-3-methylbutanoic acid [10–12]. In this work, Mannich reaction was carried out on crosslinked polyacrylamide using ethylenediamine (EDA), diethylenetriamine (DETA) and triethylenetetra- mine (TETA) and sulfomethylation reaction was carried out on crosslinked polyacrylamide to obtain ion selective hydrogels having different functional groups, for the first 0032-3861/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0032-3861(03)00033-8 Polymer 44 (2003) 1785–1793 www.elsevier.com/locate/polymer * Corresponding author. Tel.: þ90-212-591-24-80; fax: þ 90-212-591- 19-97. E-mail address: hasineka@istanbul.edu.tr (H. Kas ¸go ¨z).