Preparation,Modification And Application Of Chitosan Microspheres

In recent years,carbon microspheres have been widely used as a new carbon material in the field of catalysis and adsorption.Therefore,carbon microspheres have also been gradually developed into a hot spot for scholars.Carbon microspheres have regular spherical structure,good chemical stability and thermal stability.Carbon microspheres are considered to be a catalyst carrier and adsorbent precursor with competitive advantages and good market prospects.As a natural polymer material,chitosan is safe and non-toxic,and shows good biocompatibility,bioadsorption,biodegradability,film-forming property and hydrophilicity.The chitosan molecular chain contains a large number of amino groups and hydroxyl groups,and has good modification and reactivity.In this paper,magnetic chitosan microspheres with magnetic responsiveness were synthesized by emulsion cross-linking method,and then it was applied to the immobilization of lactase to further broaden the application range of chitosan.By modification of chitosan using quaternization with 3-chloro-2-hydroxypropyltrimethy-lammonium chloride and the quaternary ammonium salt the modified chitosan microspheres were synthesized by emulsion cross-linking method.It is used as an adsorbent in the treatment of printing and dyeing wastewater simulated by methyl orange,and then exploring its adsorption performance.The main research contents are as follows:1.Chitosan microspheres were prepared by emulsion cross-linking method using chitosan as the raw material.The chitosan microspheres were characterized by FT-IR,SEM and TG.The effects of chitosan concentration,stirring rate,oil-water ratio and crosslinking time on the morphology,particle size and structure of chitosan microspheres were investigated.Chitosan microspheres with uniform spherical shape,good dispersibility and uniform particle size were prepared when the concentration of chitosan was 3%,stirring rate was 400-500 r/min,oil-water ratio was 8:1,and crosslinking time was 4 h,,and the prepared chitosan microspheres have good thermal stability.2.The magnetic Fe₃O₄ nanoparticles were prepared by hydrothermal method.The magnetic chitosan microspheres were successfully prepared by emulsion cross-linking method using the chitosan and the synthesized Fe3O4 as the raw materials.The magnetic chitosan microspheres were characterized by SEM,FT-IR,VSM and XRD.The magnetic chitosan microspheres showed the fine spherical shape,smooth surface,good dispersion,no adhesion,and a large number of functional groups such as-NH₂,-OH.In addition,the magnetic chitosan microspheres showed good magnetic responsiveness.Then the prepared chitosan microspheres were used as the carrier to prepare the magnetic chitosan microspheres immobilized lactase.The effect of immobilization conditions on the preparation of immobilized enzymes was studied by using enzyme activity as an indicator.The results showed that the optimal immobilization conditions for lactase were:immobilization time was 4 h,pH was 7.0,and lactase enzyme concentration was 0.6mg/mL.The immobilized enzyme has a certain improvement in pH stability and temperature stability relative to the free enzyme.After repeated use for 5 times,the enzyme activity remained above 65%.3.The chitosan was modified by quaternization with 3-chloro-2-hydroxypopyltrime-thylammonium chloride,and then the modified chitosan microspheres were prepared by emulsification crosslinking method using the modified chitosan as the raw material.The SEM,FT-IR,TG and laser particle size analyzer were used to characterize the morphology and structure of chitosan microsphere modified by quaternary ammonium salt.The results showed that the chitosan microsphere modified by quaternary ammonium salt had fine spherical shape,smooth surface and uniform particle size.The crosslinking reaction mainly occurred on the amino group of chitosan,and chitosan microsphere modified by quaternary ammonium salt had good thermal stability.The printing and dyeing wastewater simulated by methyl orange were processed by chitosan?CS?,modified chitosan?HTCC?and chitosan microspheres modified by quaternary ammonium salt?Q-HTCC?,the order of removal rate of methyl orange solution was Q-HTCC?98.9%?>HTCC?90.6%?>CS?22.9%?.The effect of the amount of microspheres,the pH of wastewater,adsorption time and temperature on the adsorption properties were investigated.The results showed that the adsorption equilibrium was reached when the amount of microspheres were 15 mg,pH was 9.0,and adsorption at 35°C for 60 min.The maximum dye removal rate that can be achieved is 98.9%,It is indicated that the quaternary ammonium salt modified chitosan microspheres had good adsorption properties for the printing and dyeing wastewater simulated by methyl orange.