Preparation And Application Of Porous Cellulose-chitosan Microsphere Carrier

Natural polymers have attracted wide attention in many carrier types due to their biocompatibility,non-toxicity and biological activity.Cellulose and chitosan are the most abundant and common natural polymers,which have a wide range of applications and prospects in the field of chemical and biological materials.However,due to the large amount of intramolecular and intermolecular hydrogen bonds,they are difficult to dissolve in water and organic solvents,which greatly limits their application.In this paper,Na OH/Li OH and urea/thiourea aqueous solution（alkaline urea system）were used to dissolve cellulose and chitosan to prepare a series of microspheres,which is a green and promising method.Compared with the preparation method using ionic liquid,it is simpler and cheaper.In general,porous spherical materials have better fluidity and higher specific surface area,and are more suitable for use as carriers.The preparation of cellulose and chitosan into spheres not only improves the load,but also makes it easier to disperse and recycle evenly during use.However,the reported natural polymer microspheres have low specific surface area and are difficult to form porous surface.Therefore,in this paper,cellulose and chitosan were dissolved in alkaline urea system through freeze-thaw cycle,and then regenerated in weak alkaline system by solvent exchange.Then,a novel three-dimensional porous cellulose/chitosan composite gel spheres（CCMs）with high specific surface area（235.4m2/g-325.3m2/g）were prepared by freeze-drying method.The microspheres were characterized by Fourier transform infrared spectroscopy（FTIR）,thermogravimetric analysis（TGA）and X-ray diffraction（XRD）.The size,surface and internal morphology of the microspheres were observed by scanning electron microscopy（SEM）,and their applications as carriers were explored.As a carrier of immobilized enzymes: Low-cost,green and sustainable cellulose/chitosan composite microspheres were used to covalently immobilize α-amylase（AMY）using glutaraldehyde reagent.The results of enzyme activity test showed that glutaraldehyde reagent could successfully immobilized AMY on the composite gel microspheres,and the enzyme activity only decreased by 17.6 %。Compared with free AMY catalyst,the immobilized enzyme had higher thermal stability,wider p H adaptability and better storage stability.After 10 cycles,the immobilized enzyme still maintained its initial activity of 77.5%.The results showed that the composite microspheres could be used as a good carrier of immobilized enzyme and had good recyclability.As the carrier of Fenton-like reagent Cu S: Cu S nanoparticles microsupported by porous cellulose with the highest specific surface area were used as a recyclable biocatalyst for the degradation of organic dyes.BET results showed that Cu S still had a specific surface area and porosity of more than 230 m2/g after loading,and the load could be controlled according to different amounts of copper sources.XRD and XPS results showed that Cu S was successfully loaded on cellulose microspheres.In the decolorization degradation test of methylene blue（MB）and methyl orange（MO）,the catalytic performance is excellent.In the presence of low dose H2O2,the degradation rate of MB can reach 94.8%within 10 min.The stability test shows that the composite catalyst exhibits high catalytic activity under weak acid and alkaline conditions.After 5 cycles of degradation,the activity of the recovered catalyst is still 90.1%,indicating that the prepared Cu S@CM composite has good catalytic activity and reusability.