Study On Synthesis And Properties Of Aramid Nanofibers/Bacterial Cellulose Composite Aerogels

Aerogels exhibit wide application value and prospects in many fields such as biomedicine,construction,energy storage materials,adsorption,etc.due to its high porosity,light weight and high specific surface area,and has attracted much attention.Based on the theory of polymer design,the dissertation prepared the aramid nanofiber/bacterial cellulose composite aerogels by physical gel method and chemical gel method with the combination of bacterial cellulose and aramid nanofibers,which achieved the absorption of cationic dye solution.The composite aerogels were prepared by physical gelation method and deionized water was used as the gelling agent.In the experiment,the amount of gel reagent,the ratio of bacterial cellulose to aramid fiber and the aging process were changed to optimize the structure and properties of the composite aerogels.The structure of the composite aerogels was characterized by infrared spectroscopy,scanning electron microscopy and BET adsorption analysis.The composite aerogels have an ultra-high porosity and can reach more than 98%.At the same time,the results of the adsorption experiment showed that the composite aerogels have selective adsorption to cationic dye methylene blue.When the concentration of dye was 25 mg/L,the maximum adsorption rate of the same quality composite aerogels towards cationic dye methylene blue（MB）and anionic dye methyl orange（MO）rates were 98.8%and5.4%,respectively,and when the concentration of the dye was 150 mg/L,the adsorption rate of methylene blue by the composite aerogels could reach 70.0 mg/g.Due to the hydrogen bonding effect between the two substrates and the lack of chemical force during the composite aerogels prepared by the physical gelation method,the binding force was weak,and a large volume shrinkage was formed during the drying process,there are certain defects in the structure.In order to solve this problem,the aramid nanofibers dispersion was hydrolyzed to produce new functional groups of-NH₂ and-COOH.On the basis of physical gelation method,glutaraldehyde was added as a cross-linking agent to prepare composite aerogels,by changing the amount of hydrolyzed phosphoric acid,cross-linking agent and cross-linking temperature,analyzed its influence on the structure and properties of the composite aerogels,determined the optimal preparation conditions and the amount of raw materials.Scanning electron microscopy（SEM）results showed that after the addition of the cross-linking agent,the composite aerogels could form a denser pore structure,and the pore structure was evenly distributed.The macroscopic structure might also clearly see that the volume shrinkage of the composite aerogels was reduced.It increased the specific surface area of the composite aerogels to a certain extent.The test results of BET adsorption showed that the ANFs/BC composite aerogels prepared by the physical gelation method was a mesoporous material.When the concentration of the methylene blue solution was 25 mg/L,the maximum adsorption rate of the composite aerogels could be reached 98.8%.The adsorption kinetics and isotherm model were used to analyze the adsorption performance of the composite aerogels towards the cationic dye methylene blue solution.The results revealed that the composite aerogels adsorbed the methylene blue adsorption Pseudo-second-order kinetic model and the Langmuir isotherm model,the thermodynamic equations showed that the adsorption reaction was spontaneous and exothermic reaction.