Removal of Toxic Cr(VI) Ions from Aqueous Solution Using Nano-hydroxyapatite-based Chitin and Chitosan Hybrid Composites

In the present investigation, bio-inorganic composites composed of nano-hydroxyapatite (n-HAp) with chitin and chitosan have been prepared and used for the removal of chromium(VI) ions from aqueous solution. Such composites exhibited a higher Cr(VI) ion sorption capacity than the individual components. The sorption capacities of n-HAp, n-HAp/chitin (n-HApC) composite and n-HAp/chitosan (n-HApCs) composite were found to be 2720, 2845 and 3450 mg/kg, respectively. Batch adsorption studies were conducted to optimize various equilibrating conditions such as the contact time, pH and co-ions. The sorbents were characterized by FT-IR spectroscopy, BET and EDXA analysis. The sorption process could be fitted by both the Freundlich and Langmuir isotherm models. Standard thermodynamic parameters such as the Gibbs' free energy change, Delta G(0), the standard enthalpy change, Delta H-0, and the standard entropy change, Delta S-0, were calculated in order to obtain an understanding of the nature of the sorption process. The kinetics of the reaction could be fitted by the pseudo-second-order and intra-particle diffusion models. The mechanism for Cr(VI) ion sorption onto the composites was established.