| Cross-linked porous starch is widely used in many fields because of its excellent physical and chemical properties. At present, holes of cross-linked porous starch are made by the enzymatic hydrolysis method, but the method is costly, the reaction time is long, and the distribution of pore size is nonuniform. And also the structure and properties of cross-linked porous starch are influenced by the amount of enzyme, temperature, pH, reaction time and the concentration of starch. Therefore, in order to improve the adsorption performance, the preparation methods of cross-linked porous starch were studied in the thesis.Cross-linked porous starch (ECPS) was prepared by crosslinking from soluble starch (SS) through water-in-oil emulsion, with cyclohexane as the oil phase. The conditions of preparation were optimized by experiment, and the properties of ECPS were compared with porous starch prepared by the enzymatic hydrolysis method. A large number of micropores could be seen with scanning electron microscopy. FTIR scanning showed that crosslinking reaction was successful XRD analysis showed that the degree of crystallinity was reduced from26%to8%. The specific surface area of ECPS was3.456m2/g, oil absorption rate was up to162%, and the maximum saturated adsorption capacity for methylene blue was145mg/g at286K. Compared with the porous starch prepared by the enzymatic hydrolysis method, the specific surface area of ECPS increased1.6times, oil absorption rate increased0.7times, and maximum saturation adsorption capacity for methylene blue increased nearly4times.Cross-linked porous starch (FDPS) was prepared by vacuum freeze-drying method, through crosslinking reaction. The aperture of porous starch (PS) prepared by vacuum freeze-drying method is very large (about several tens of micrometers). The adsorption properties of PS are poor, when it is used as adsorbent. Therefore, PS was modified by crosslinking. FDPS was prepared by vacuum freeze-drying method, with N, N-methylene-bis-acrylamide as the crosslinking agent. SS dissolved under100℃, and then with the effect of the initiator, crosslinking reaction happened. The properties of FDPS were compared with ECPS. Macropores with three dimensional cut-through and the uniform dense micropores covered with macropores walls was seen through scanning electron microscopy. FTIR scanning showed that there were amide groups on the FDPS, and crosslinking reaction was successful. XRD analysis showed that crystallinity was reduced. TGA analysis showed thermal stability improved. The specific surface area of FDPS was15.954m2/g, oil absorption rate was up to422%, and the maximum saturated adsorption capacity for methylene blue was233mg/g at286K. Compared with ECPS, the specific surface area of FDPS increased3.6times, oil absorption rate increased1.6times, and maximum saturation adsorption capacity for methylene blue increased nearly0.6times.ECPS and FDPS as dye adsorbent, the adsorption properties and adsorption mechanism were investigated, and the effect of temperature on adsorption capacity was studied. Adsorption of methylene blue by ECPS and FDPS conformed to Langmuir. Compared with ECPS, the adsorption rate of FDPS was faster, and the removal of methylene blue was more thorough under the same concentration of dye. Through hydrogen bonding, ECPS and FDPS adsorbed dye, as a rapid equilibrium process. As the temperature rose, adsorption properties of FDPS and ECPS for methylene blue decreased. |
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