| Chitosan were adopted to prepare spherical chitosan beads by reversed-phase suspension technique. The preparation procedures were optimized. And, the physicochemical properties of the spherical chitosan beads were studied. First, chitosan was prepared by the acidification and de-acetyl reaction with raw materials, e.g., the shell of shrimp and crab. The satisfactory chitin could be prepared under such conditions as 4% of the hydrochloric acid, 85℃ of the reaction temperature and 8 h of the reaction time. Moreover, the resultant chitosan was prepared by treating the above chitin with 50% of the aqueous sodium hydroxide for 4 h at 90℃. Under the above optimum conditions, the average de-acetyl rate of the resultant chitosan could reach 90.05%. Second, chitosan beads were prepared by the chitosan with the reverse-phase suspension technique. The satisfactory chitosan beads could be prepared under such conditions as 2.5% of Span 80, 0.75% of Tween 80 and 45g of glutaraldehyde by adopting the 80g of 5% chitosan solution in 150 mL of transformer oil at 40 ℃ for first 2h and 85℃ for another 3h. And the yield of the prepared chitosan beads could reach 85.77% with 1.681 of the uniformity and 0.152 mm of the effective grain size. The water ratio of the chitosan beads could reach 69.8% with 203 m2·g-1 of the specific surface area and 1.68 mmol·g-1 of the full exchange capability. They also have some absorb capability and couldn't be soluted by acid. At the last, the adsorption properties of the chitosan beads were comprehensively studied in two ways of static adsorption and mobile adsorption. And, the effect factors were also optimized. Moreover, the adsorption mechanisms, i.e., the adsorption thermodynamics and kinetics were explored. The adsorption of such amino acids as Gly,Lys,Ala on the chitosan beads has found to be concentration,pH and tenperature dependent. The chitosan beads showed excellent adsorption capacities for the above amino acids. The adsorption capacities could reach 89.2 mg?g-1,63.7mg?g-1 and 55.8 mg?g-1respectively. The static adsorption processes followed the Langmuir and Freundlich adsorption isotherm equations. It could be concluded from the adsorption thermodynamics and kinetics that the physical adsorption was predominant in the adsorption process of amino acids on the chitosan beads. The adsorption rate was controlled by two diffusion models of surface diffusion process and intraparticle diffusion process, but the intraparticle diffusion process played a more significant role during the adsorption process. Consequently, the chitosan beads will have a prospective application in the adsorpetion and purification field owing to its excellent adsorption properties and its renewable and abundant raw materials. |
