Removal of Cr(VI) ions using a binary grafting of N-vinylcaprolactam and N,N -dimethylacrylamide onto crosslinked chitosan, synthesized by gamma radiation

Abstract

Chitosan is characterized by its good affinity of metal ions due to high amount of amino groups. However, crosslinking of chitosan results in a dramatic decrease of retention properties due to reaction of amino groups during process. N,N-dimethylacrylamide (DMAAm) increases the hidrophilicity of the system and improve the apparent mechanic properties; while N-vinylcaprolactam (NVCL), a temperature stimuli sensitive monomer with a LCST of about 32 ^oC, makes possible for reuse the material. Adsorption of Cr(VI) onto crosslinked chitosan (net-CS) and NVCL/DMAAm binary grafted system onto net-CS, synthesized by gamma radiation of ⁶⁰Co, has been investigated. The experimental results obtained from equilibrium adsorption studies are fitted in Langmuir and Freundlich isotherms. The Langmuir model agreed better, indicating that adsorption process is carried out homogeneously onto surface. The maximum adsorption capacity was 24.63 and 55.2 mg g^-1 for net-CS (1%) and net-CS (3%), respectively. The maximum retention was obtained from the binary grafted system (21%) onto net-CS (3%) with 142.86 mg g^-1.