Study On The Construction And Adsorption Properties Of Chitosan-anionic Polysaccharide Composite Gels

Heavy metals and dye pigments are the main pollutants of industrial wastewater in the fields of food,printing and dyeing,which are also a kind of common food safety hazards.The use of biosorbents to remove the pollutants has the advantages of high efficiency,low cost and convenient operation.Chitosan(CS)has strong affinity for heavy metal ions and organic dyes,but the single-component biosorbent constructed by chitosan alone has certain limitations in mechanical stability and adsorption performance.The amphoteric polyelectrolyte composite material constructed by chitosan and anionic polysaccharides which rich in carboxyl or sulfate groups is helpful to improve the stable mechanical properties and broad-spectrum adsorption properties of chitosan gel.Therefore,the design and development of chitosan-anionic polysaccharide composite gel biosorbent is an effective way to control the safety of food pollutants,which is of great significance and necessity to improve the safety of food raw materials and food processing.In this thesis,CS was blended with gum arabic(GA),sodium alginate(SA),carboxymethyl cellulose(CMC)and fucoidan(FU)by alkali/urea aqueous solvent,respectively,to construct the composite gel which prepared by chemical crosslinking in the alkali dissolution system.Besides,CS was blended with gellan gum(GG)to construct a composite gel in garbage enzyme which is the acid dissolution system.In this work,the preparation process parameters of a series of chitosan-anionic polysaccharide composite gels constructed by two dissolution systems were optimized,and their structural morphology,adsorption performance and adsorption mechanism were studied.The main research contents and conclusions are as follows:(1)CS-GA,CS-CMC and CS-FU composite gels were prepared by using polyethylene glycol diglycidyl ether as crosslinking agent in alkali/urea dissolution system.The results of single factor experiment and response surface optimization experiment showed that the optimum process conditions of CS-GA were m(CS):m(GA)=1.09:1,crosslinking time 5 h,crosslinking temperature 55℃;the optimum process conditions of CS-CMC gel were m(CS):m(CMC)=5:1,crosslinking agent concentration 8.24%,crosslinking temperature 35℃;the optimum process conditions of CS-FU gel were crosslinking temperature 45℃,m(CS):m(FU)= 4:1 and crosslinking agent concentration 10%.The optimal process conditions of the above series of gels are close to the theoretical values predicted by the model,which has practical value.(2)The adsorption capacity and adsorption mechanism of heavy metal ions Cu(Ⅱ)and congo red(CR)were investigated for CS-GA,CS-SA,CS-CMC and CS-FU prepared in low temperature alkali/urea dissolution system.The results showed that the four chitosan-anionic polysaccharide gels had multi-scale porous structure,and their specific surface area and pore volume were higher than those of single chitosan gel.The adsorption process of Cu(Ⅱ)and CR on CS-GA,CS-SA and CS-CMC was surface monolayer adsorption controlled by chemical action,while CS-FU had both physical adsorption and chemical adsorption.CS-CMC and CS-SA had the highest adsorption capacity for Cu(Ⅱ)and CR,and the maximum saturated adsorption capacity was 22.5mg/g and 833.3 mg/g,respectively.CS-FU showed high adsorption performance for Cu(Ⅱ)and CR,and the maximum saturated adsorption capacity was 19.8 mg/g and 714.2 mg/g,respectively.The adsorption mechanism of a series of chitosan-anionic polysaccharide gels on heavy metal Cu(Ⅱ)and CR dyes was based on chemical chelation and electrostatic attraction,respectively.The addition of different anionic polysaccharides is expected to expand the application of chitosan adsorbents in the field of food processing and safety.(3)The chitosan-gellan gum composite gel(CS-GG)was prepared,using CS and GG as raw materials,garbage enzyme as solvent system,genipin/polyethylene glycol diglycidyl ether(PGDE)as composite crosslinking agent.The effects of crosslinking temperature,CS/GG mass ratio and genipin/PGDE mass ratio on the hardness of composite gel were studied by single factor experiment and Box-Behnken response surface method.The results showed that the optimum process parameters for the preparation of composite gel in the garbage enzyme dissolution system with acidity of 1.8% were crosslinking temperature of 60℃,mass ratio of CS to GG of 1:3,and mass ratio of genipin to PGDE of 4.3:1.CS-GG prepared under this condition had a porous three-dimensional network structure.The adsorption process of Cu(Ⅱ)by CS-GG was a surface monolayer adsorption dominated by chemical chelation.The maximum saturated adsorption capacity of Cu(Ⅱ)was 7.0 mg/g.Besides,it showed obvious antibacterial activity against Escherichia coli and Staphylococcus aureus.The construction of the composite gel is not only expected to expand the new application of garbage enzyme,but also provide new ideas and technical references for the construction of chitosan-based antibacterial adsorbents.