Covalent Chitosan Gels for Efficient Iron (III) Ion Adsorption

Abstract

Synthetic and natural polymers are suitable metal ion adsorbents for various purposes like wastewater or drinking water treatment, biomedical applications, and industrial applications like production of some household chemicals. Synthetic polymers have advantages like being durable under severe conditions but they are not suitable especially for biomedical applications since they usually lack biocompatibility. Furthermore almost all synthetic polymers are petrochemical derivatives. Chitin is the second most abundant natural polymer, which can be obtained from the shells of sea animals. These shells contain 30% of chitin; the rest being different proteins and minerals. Chitosan that can be obtained by N-deacetylation of chitin, is a copolymer of β-linked 2-acetamido-2-deoxy-α-D-glucose and 2-amino-2-deoxy-α-D-glucose residues. Chitosan is a natural aminopolysaccharide and it has complex formation and ion adsorption properties. It is also a biocompatible, biodegradable and mucoadhesive natural polymer and therefore has a great potential for biomedical applications. In this study, N-phthaloylated chitosan was phosphorylated by a chemical reaction using sodium triphosphate (Na5P3O10) as the phosphorylating agent and urea as a catalyst. The stability of the product in aqueous medium was improved by applying chemical crosslinking using ethylene glycol diglycidyl ether (EGDE) as the crosslinking agent. The product was then dephthaloylated to obtain an amine rich phosphorylated chitosan. All products obtained were characterized by FTIR spectrometry. Phosphorylated and EGDE – crosslinked chitosan was tested as an Fe3+ adsorbent in aqueous solution. The Fe3+ adsorption was followed by visible spectrometry at 505 nm. The EGDE – crosslinked phosphorylated chitosan product proved to be a successful Fe3+ adsorbent and was calculated to have an equilibrium adsorption capacity of 140 mg Fe3+/g adsorbent.