Metal ions binding by chelating ligands from new polymer bearing amidoxime functional groups

Abstract

Chelating polymer materials are mainly used in analytical, industrial and radiochemical laboratories, but only to a limited extent in solving environmental problems. Metal pollution of the environment presents a unique problem, since metals are not subjected to biodegradation. The chelating resins containing amidoxime groups have been playing a vital role in environmental monitoring of toxic trace metals. The amidoxime chelating resins can be used for extraction of toxic metals in the environment and sewage waters. The possibility of uranium recovery from seawater has been studied in many countries, a particularly high number of publications come from Japanese scientists, which contain the synthesis of macroreticular resins bearing amidoxime groups, because of their use in extraction of uranium from seawater. 1‐4 Most of these papers involve the incorporation of a nitrile group into a polymer matrix, followed by the conversion of the nitrile group into an amidoxime group using the alkaline solution of hydroxylamine. Egawa et al. 5 prepared a macroreticular chelating resin containing amidoxime by reacting acrylonitrile-divinyl benzene copolymer with hydroxylamine. Kubota and Shigehisa 6 proposed a new route in which amidoxime groups were prepared by the reaction of cyanoethylcellulose and acrylonitrile grafted cellulose with hydroxylamine. Fetscher 7 described the extraction of metals from dilute solutions by poly(amidoxime) resin derived from fibrous homopolymers and copolymers of acrylonitrile. Divinylbenzene cross-linked poly(acryloamidoxime) resins were obtained and successfully used in the determination of trace metals in natural waters. 8,9 Most of the work centralised on the uranium extraction in sea water by poly(amidoxime) resin. There are very few articles published for transition metal uptake by poly(amidoxime) resin. This may first be introduced by the preparation of poly(amidoxime) chelating resin from polyacrylonitrile (PAN) grafted sago starch. In this report, the PAN grafted copolymer was used as a cheapest starting material to obtain the poly(amidoxime) resin and the binding property of the chelating resin was examined with a series of metal ions. The PAN grafted sago starch was prepared from acrylonitrile monomer and sago starch using the free radical initiating process according to the reaction mechanism suggested by Ceresa. 10 The grafting procedure was described elsewhere. 11 The optimum yield of PAN grafted copolymer at the concentration of ceric ammonium nitrate, acylonitrile, sago starch (AGU, anhydroglucose unit) and sulfuric acid were 9.52 〈 10 ‐3 , 0.506, 0.146 and 0.190 mol/l respectively, as well the reaction temperature and period were 50°C and 90 min, respectively. The conversion of the nitrile group into amidoxime was carried out by the treatment of hydroxylamine in an alkaline medium. According to the mechanism suggested by Schouteden, 12 the reaction of PAN with hydroxylamine is shown in Scheme 1, where P is the backbone polymer.