Removal of Cadmium (II) from aqueous solution using tripolyphosphate cross-linked chitosan

Finding an economical technique for Cadmium (Cd (II)) removal from aqueous solution through an environmentally friendly method has always been of great importance. To this aim, chitosan and sodium tripolyphosphate cross-linked chitosan beads were prepared for Cd (II) uptake from aqueous media. Chitosan with different cross-linking ratio was synthesized via changing the concentration of sodium tripolyphosphate solution (5, 10, and 15 % (w/v)). Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction were then implemented to characterize chitosan and tripolyphosphate cross-linked chitosan beads. Investigating thermodynamic parameters proved the feasibility and spontaneity (ΔG0>0), endothermic nature (ΔH0>0) and randomness increase at solid/solution interface (ΔS0>0) of the adsorbents. The experimental adsorption data for cross-linked chitosan were fitted to isotherm models out of which the Langmuir model showed the best fit. Lastly, factors influencing Cd (II) adsorption onto adsorbents, including temperature and crosslinking extent, were studied in detail by employing Response Surface Methodology (RSM). The quadratic regression model was in good agreement with experimental data (R2 = 0.95). The designed model suggested that the maximum adsorption capacity of 99.87 (mg/g) is achievable at 55 ℃ and 2.92 % (w/v) crosslinking degree, which was higher than the frequent cross-linked chitosans investigated by other researchers.