Catalytic Degradation Of Chitosan Into Low Molecular Water Soluble Chitosan

Chitin is the second most abundant natural biopolymer on earth after cellulose. Chitosan, which derived from full or partial deacetylation of chitin, is a cationic biopolymer. However, the utilization of chitosan has been limited because of its high molecular weight, water-insolubility and high viscosity of its solution. Compared with chitosan, low molecular water soluble chitosan(LMWSC) without altering the structure has much improved its viscosity and water-solubility. And some special biological, chemical and physical properties offer much potential applications in many fieldssuch as waste water treatment, agriculture, pharmaceuticals, food additives et. al. Several methods are available to degrade the chitosan and continuous attention is drawn to newer and greener methods of oxidative degradation. Catalytic oxidation with hydrogen peroxide is particularly attractive from the environmental and economical benefits. In this thesis, we mainly do some work about the catalyst and active species in the degradation of chitosan.An ionic liquid catalyst [Bmim]3PW12O40has been synthesized and characterized. The catalytic oxidative degradation of chitosan was studied under orthogonal test with this system.the results indicated that the dosage of catalyst was the main factor to the degradation of chitosan, while the volume of H2O2and time had little effect. The optimum reaction conditions were determined as follows:H2O21.5mL, reaction temperature75℃, dosage of [Bmim]3PW12O400.006g, reaction time30min.The isolated peroxo species (TBA)3{PO4[WO(O2)2]4} and K2[W2O3(O2)4] were directly employed as the catalyst to degrade chitosan. We demonstrated that not only the peroxo species{PO4[WO(O2)2]4}3-,but also [W2O3(O2)4]2-are highly efficient catalysts. The peroxo species itself can efficiently degrade the chitosan without hydrogen peroxide. And the capture of OH and comparison experiment on thedegradation of chitosan indicated that the unit of W(O2) was the active sites for oxidative, H2O2played the role to regenerate the active sites.We further investigated the isolated peroxo species (TBA)3{PO4MoO(O2)2]4} and K2[Mo2O3(O2)4] in the degradation of chitosan. The peroxo species itself can efficiently degrade the chitosan without hydrogen peroxide. And the peroxo species (TBA)3{PO4[MoO(O2)2]4}switched from pale yellow to gray blue was clearly observed during thr reaction. After the addition of excess H2O2and subsequent oxidation at room temperature for12h, the colour of the catalyst turned pale yellow again. The FT-IR, XRD indicated that the unit of W(O2) was the active sites. H2O2was found to play a fatal role in the regeneration of Mo(O2) through the capture of OH. Moreover,(TBA)3{PO4[MoO(O2)2]4} can be recovered and reused four times without loss of reactivity.