Synthesis of chitosan-organophilic layered silicate nanocomposite hydrogels and their use in heavy metal removal

In this project, organophilic nano clay structure was obtained by immobilization of spirulina algea onto NAMMT nano filler surface so that the surface area of spirulina algea was increased. Chitosan nanocomposite hydrogels were prepared by the interaction of modified MMT (Sp-MMT) and chitosan biopolymer. Chitosan polymer was converted to hydrogel form by the physical crosslinking without using any organic crosslinking agent. Spirulina algea contributed chitosan polymer to intensive physically crosslinked in itself by functional groups. In this project, our objective was to enhance metal adsorption and swelling properties of chitosan composite hydrogels by the immobilization of Spirulina microalg into/onto the clay to obtain an organophilic clay (Sp-MMT). The effect of increased MMT clay loading in thermal and morphological properties were investigated by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM), respectively. Chromium metal adsorption capacity was determined with UV-VIS spectrophotometer. All the Sp-MMT loaded nanocomposite hydrogels exhibited higher swelling and metal adsorption capacities compared to neat chitosan hydrogel and NaMMT loaded hydrogels. Chitosan nanocomposite hydrogel, CH-1SpM having 1wt% Sp-MMT clay was found to have maximum swelling, enhanced thermal stability and maximum adsorption capacity. Literature data reports that Spirulina and MMT clay by themselves can remove only about 4.80 % and 0.36 % Cr (VI) ion, respectively, with respect to their weights. On the other hand, the CH-1SpM hydrogel adsorbed about 3800 % Cr (VI) ion with respect to Spirulina‟s weight in it. Moreover, the maximum adsorption value of the same hydrogel was found to be about 175 % higher than that of neat hydrogel. Enhancement of the water swelling and metal adsorption capacities by Sp-MMT loaded hydrogels was ascribed to the open network structure of Spirulina maicroalg interacting with chitosan matrix and so maximized interaction with water molecules and chromate anions.