Preparation And Application Of Cellulose Aerogel Based On Ionic Liquid

Aerogel is a kind of three-dimensional porous material obtained by removing the liquid solvent without changing the network.Cellulose aerogels,possessing the unique hydrogen bond network structure,excellent biocompatibility and biodegradability,make up the shortcomings of traditional inorganic aerogels and polymeric aerogels and become promising environment-friendly porous materials.Cellulose is widespread,abundant and degradable,and the cellulose chains contain numerous active hydroxyl groups which can form a stable three-dimensional structure through the intramolecular and intermolecular hydrogen bonding interactions.So cellulose endows cellulose aerogel with a variety of special properties.However,many limitations impede the application of cellulose aerogels,including the limited methods of biomass utilization,the complex approaches of cellulose aerogel fabrication,the toxicity and corrosiveness of the used solvents,and the difficulty of solvent recovery.This dissertation aims to fabricate cellulose aerogels from different raw materials based on ionic liquid systems,and develop green and facile preparation approaches.Furthermore,through exploring the formation mechanisms to obtain high performance cellulose-based aerogels and expand the applications of cellulose aerogels.The main innovation and achievements are as follows:(1)Nano-cellulose aerogel and regenerated cellulose aerogel were prepared.Firstly,the rod nanocellulose with a length of 100-200 nm and a diameter of 10-15 nm was prepared.The nanocellulose was uniformly dispersed in water to form colloids.The ζ potential of nanocellulose colloid was ±35 mV which is stable enough to store for a long time without aggregation or precipitation.When the concentration of nanocellulose is 12%,the colloid becomes gelation.The nanocellulose aerogel(cellulose 1)obtained by lyophilization.Second,the regenerated cellulose aerogel(cellulose II)was prepared using ionic liquid,through the screening of ionic liquids,[Amim]Cl was found to be a good cellulose solvent which can dissolve cellulose under 70 ℃ in 30 min and the cellulose regeneration rate is as high as 93.7%.The compressive strength of cellulose aerogel is 63.7 N/cm2;The regenerated cellulose aerogels were prepared from microcrystalline cellulose,cotton fiber and corn stalk,respectively.The microstructure of regenerated cellulose aerogels prepared from microcrystalline cellulose and cotton fiber were uniform with the interlaced fibers;the fibers in the regenerated cellulose aerogel prepare from corn stalk has cladding,because the corn stalk contains large amounts of lignin and hemicellulose.(2)The preparation and mechanism of cellulose composite aerogels were studied.The cellulose/ZnO aerogel was fabricated through a facile approach based on ionic liquid and diethylene glycol.The uniform and adjustable spherical ZnO nanoparticles were synthesized in situ on the cellulose which solves the problem occurred in the traditional fabrication of cellulose/ZnO aerogel materials,such as the solvents were not environment-friendly and the ZnO particles accumulated excessively.The mechanism of synthesize ZnO in situ was simulated and confirmed further.The simulation showed there was interaction between Zn2+ and-OH of glucose.With the increase of zinc acetate concentration and hydrolysis time,ZnO nanoparticles gradually nucleate and grow up.Large particles blocked the aerogel pores,resulting in a decrease of specific surface area of aerogel.By adjusting the concentration of zinc acetate and the hydrolysis time,the cellulose/ZnO aerogel had high specific surface area(271 m2/g),and the ZnO spherical nanoparticles are uniformly distributed with uniform size.Cellulose/ZnO aerogel can be used as a recoverable catalyst to effectively degrade polyethylene terephthalate.The conversion of bis(2-hydroxyethyl)terephthalate monomer was 100%and the yield was 78%which showed a high catalytic effect.After the three degradation cycles,the aerogel showed nearly no shrinkage and deformation.Compared with traditional catalysts,aerogels can be taken out without separation and make it easy to reuse in subsequent cycles.This work provides a facile approach to fabricate cellulose/metal oxide composite aerogel and explores the potential application of aerogels as catalysts.(3)The preparation of cellulose aerogel from stalks was studied.Based on the halogen ionic liquid and sulfamic acid solvent systems,the cellulose-rich aerogel was prepared by a facile and simple approach,whereby remove the lignin from the stalks in one step.The effects on cellulose aerogel properties were investigated,including different ionic liquid solvent systems,component content,morphology,thermal stability and specific surface area.[Amim]Cl and sulfamic acid solvent system can remove the lignin from corn stalks in one step,and obtain a cellulose-rich aerogel in which the cellulose content was as high as 88.11%.The prepared cellulose-rich aerogel has three-dimensional structure with high specific surface area(201 m2/g),and possess sufficient thermal stability and compression strength.It has good adsorption effect on anionic dye(Congo red)and cationic dye(Coomassie brilliant blue),and the saturated adsorption capacity is 549.13 mg/g and 301.58 mg/g,respectively.The adsorption mechanism was simulated.The results showed that Na in Congo red and-OH in glucose displayed the strongest hydrogen bond than the π-πinteractions and the interaction between-HSO3-of Coomassie brilliant blue with glucose.This work provides a simple and facile approach to prepare of cellulose aerogel from lignocellulosic biomass and explores the application of cellulose aerogel materials in the field of dye adsorption.(4)The preparation of cellulose aerogel separators from polyester-cotton blended fabrics was studied.Based on alcohol hydrolysis and ionic liquid dissolution,the cellulose aerogel separators were prepared from polyester-cotton blended fabric which was used in supercapacitors.The polyester-cotton blended fabric can be degraded in ethylene glycol under the action of a catalyst to obtain cotton fiber,wherein the cotton fiber recovery rate was as high as 86.59±6.47%.By investigating the properties of cellulose aerogel separators with different cellulose concentration,it was found that the separator with 2%cellulose has the optimal properties.This aerogel separator consists of interlaced cellulose with the diameter of 10-20 nm,and possesses high specific surface area(210 m2/g)and elongation at break(28.4%).The performance of cellulose aerogel separators and commercial PP separators were compared.The shrinkage rate of cellulose aerogel separator was less than 1%under 160 ℃,while that of PP separator was approximately 39%.The excellent stability of cellulose aerogel separator ensures the safety of the supercapacitor.Moreover,the high thermal stability[Emim]TFSI ionic liquid electrolyte was synthesized,and the cellulose aerogel separators have better electrolyte wettability than PP separators.Furthermore,the prepared supercapacitor has good cycle performance,low impedance and good characteristics.