Competitive Removal of Nickel (II), Cobalt (II), and Zinc (II) Ions from Aqueous Solutions by Starch-Graft-Acrylic Acid Copolymers Gamze Gu ¨c ¸lu ¨, 1 Kubilay Gu ¨c ¸lu ¨, 2 Sibel Kele¸ s 1 1 Department of Chemical Engineering, Faculty of Engineering, Istanbul University, 34320 Avcılar, Istanbul, Turkey 2 Department of Chemistry, Faculty of Engineering, Istanbul University, 34320 Avcılar, Istanbul, Turkey Received 15 December 2006; accepted 1 June 2007 DOI 10.1002/app.26866 Published online 17 July 2007 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Graft copolymerization of acrylic acid (AA) onto starch was carried out with ceric ammonium nitrate as initiator under nitrogen atmosphere. The grafting percen- tages (GP%) of starch-graft-acrylic acid (St-g-AA) copolymers were determined. The effect of GP% of St-g-AA copolymers on the competitive removal of Co 2þ , Ni 2þ , Zn 2þ ions from aqueous solution was investigated at different pH (2, 4, 6). The concentrations of each ion in aqueous solution 5 mmol/ L. Effects of various parameters such as treatment time, ini- tial pH of the solution and grafting percentage of starch graft copolymers were investigated. Metal ion removal capacities of St-g-AA copolymers increased with GP% of the copoly- mers and pH. The results show that the removal of metal ions followed as given in the order Co 2þ > Ni 2þ > Zn 2þ . In this study, metal ion removal capacities were determined by atomic absorption spectrophotometer (AAS). Ó 2007 Wiley Periodicals, Inc. J Appl Polym Sci 106: 1800–1805, 2007 Key words: starch; acrylic acid; heavy metal ion removal; graft copolymers INTRODUCTION Starch has been the raw material of scientific and indus- trial studies for many decades, due to its low cost and biodegradability. Many chemical modifications of starch have been carried out for its use. Chemical modi- fication of starch via grafting of vinyl monomers is one of the most effective methods to incorporate desirable properties into starch without sacrificing its biodegrad- able nature. 1 Grafting of acrylamide, 2–5 acrylonitrile, 3,6,7 methylacrylonitrile, 1 alkyl methacrylates, 8,9 vinyl ketones, 10 2-(dimethylamino)ethyl methylacrylate, 11 acrylic acid (AA) 12–14 onto starch has been investigated. Starch graft copolymers have been used as hydrogels, 14 flocculants, 15,16 ion exchangers. 17,18 The removal of toxic and polluting heavy metal ions from aqueous solutions has been given much more attention over the past few years. The removal of heavy metal content of waters because of their toxic effects on living organisms is extremely important. The toxic na- ture of heavy metals, even at trace level in natural waters has been a public health problem for many years. The presence of heavy metal ions in industrial waste waters has been of great concern in terms of envi- ronmental protection because of toxic properties and other harmful effects on living organisms. 19 Various methods exist for the removal of heavy metals from industrial water and natural water such as chemical precipitation, ion-exchange, and reverse osmosis tech- niques. 20 Graft copolymers of natural polysaccharides such cellulose 21–23 and starch 24–28 have been used in re- moval of heavy metal ions. In this work, we describe the competitive removal of nickel (II), cobalt (II), and zinc (II) ions from aque- ous solutions. Competitive ion removal was aimed since the natural and industrial water rarely contain a single metal. For this purpose, various factors affecting the removal of heavy metal ions, such as treatment time with the solution, initial pH of the so- lution, and grafting percentage of starch graft copolymers, were investigated. The concentration of each ion in aqueous solution was 5 mmol/L. EXPERIMENTAL Materials Maize starch (food grade) was dried at 1108C and then was stored in vacuum desiccator. Acrylic acid (AA) (Merck, Germany) was purified by vacuum distillation, and then was stored in refrigerator. Ceric ammonium nitrate (CAN) (Merck, Germany) was dried at 1108C and then was stored in vacuum desic- cator. Nickel(II), cobalt(II), and zinc(II) nitrate (Merck, Germany) were analytical grade. Rest of the materials was chemically pure grade. All solutions and standards were prepared using distilled water. Correspondence to: Gamze Gu ¨c ¸lu ¨ (gguclu@istanbul.edu.tr). Journal of Applied Polymer Science, Vol. 106, 1800–1805 (2007) V V C 2007 Wiley Periodicals, Inc.