| Cellulose is the oldest natural polymer on the earth and the most abundant renewable resource in nature.It is cheap,easy to be degraded by microorganisms,and does not cause second pollution to the environment.For a long time,its development and utilization had been a research hotspot for scientific researchers.In the past few decades,various cellulose-based materials have been developed.Among them,cellulose-based aerogels have attracted great attention,and have become one of the main research objects in recent years.Similar to various aerogels,cellulose-based aerogels have the characteristics of high porosity,large specific surface area and low density,and have good structural stability in water and most organic solvents.Therefore,cellulose-based aerogels have broad application prospects in environmental purification and other fields.However,the single physical and chemical properties of cellulose make its functionality extremely limited.Although the cellulose aerogels can be endowed with functionality by chemical modification,the complex modification methods,harsh experimental conditions and the use of various chemicals undoubtedly increase the difficulty and cost of the experiment.Therefore,how to expand the versatility of cellulose aerogels through simple and environmentally friendly experimental methods,to realize the high-value utilization of cellulose,and to explore its microstructure regulation mechanism have strong practical significance and scientific value.In this thesis,Microcrystalline cellulose(MCC)was used as raw materials to prepare MCC aerogels by dissolving,regenerating and drying cellulose,so as to explore the microstructure regulation mechanism of MCC aerogels.On this basis,through the use of small molecules in-situ polymerization,macromolecular surface modification,physical intercalation modification,and self-assembly methods to control and design the microstructure of cellulose-based aerogels,and the effects of different modification methods on the micropore structure and chemical properties of cellulose-based aerogels were explored.Finally,the multifunctional cellulose-based aerogels with potential applications in both the environmental and energy fields were obtained.The main results are as follows:(1)MCC aerogels were prepared by MCC dissolution,regeneration and freeze-drying,and the effects of different preparation conditions on the regeneration aerogels were discussed.The results showed that gels could not be formed when the mass concentration of cellulose was too low(< 0.2 wt%),and the strength of MCC hydrogel increased significantly with the increase of cellulose mass concentration.On this basis,the adsorption performance of MCC aerogels with different concentrations on different dyes was studied,and it was found that they only showed excellent adsorption performance on anionic dyes Congo red(CR),but could not adsorb other anionic and cationic dyes.The adsorption mechanism is mainly due to the fact that CR molecules are attracted to O-H groups of the cellulose aerogel by formation of hydrogen bonding with aromatic rings,nitrogen and oxygen atoms.With the increase of cellulose aerogel density,the adsorption performance of MCC aerogel to CR slightly decreased.The adsorption isotherms and adsorption kinetics simulation calculations showed that the MCC aerogel adsorption to CR follows Langmuir model and pseudo-second-order kinetic model,and the theoretical maximum adsorption amount was 448.43 mg/g.In addition,selective adsorption test showed that MCC aerogels can selectively adsorb CR from anion/anion or anion/cation mixture solutions.(2)Bionic functionalized MCC/PDA composite aerogels were prepared by using dopamine(DA)in situ self-polymerization at high temperature to form polydopamine(PDA)modified MCC.The morphology characterization indicated that the porous morphology of composite aerogels was affected by the PDA content.With the increase of PDA content,the average pore size of MCC/PDA composite aerogels gradually decreased.The adsorption test results showed that the MCC/PDA composite aerogels have good adsorption performance for the cationic dye Methylene blue(MB)and strong p H dependence,the alkaline conditions were more conducive to the adsorption of MB.This is mainly due to the increased degree of deprotonation of PDA functional groups at high p H,which increases the electrostatic interaction between MCC/PDA composite aerogel and MB.In addition,the MCC/PDA composite aerogel had excellent adsorption selectivity,and the UV absorption spectrum showed that it can selectively adsorb MB from the mixed solution of anion/cation and cation/cation with a mass ratio of 1:1,and its removal efficiency up to 99% and 96% respectively.(3)A new composite aerogel composed of regenerated MCC and PPy was prepared by in-situ chemical oxidation polymerization of polypyrrole(PPy)in MCC hydrogel.The microstructure characterization showed that PPy nanoparticles dispersed uniformly in aerogels,and the presence of PPy had no significant effect on the porous structure of the MCC/PPy composite aerogel.The adsorption behaviors of MCC/PPy composite aerogels on several different organic dyes were compared,and the results showed that compared with pure MCC aerogels,the adsorption capacity of MCC/PPy composite aerogels on both cationic and anion dyes was greatly improved.On this basis,anion dyes CR and Methyl orange(MO)as well as cationic dye Safranine T(ST)was further tested.The results showed that there was a strong p H dependence on the adsorption of the three organic dyes.Acid conditions were favorable for the adsorption of anionic dyes CR and MO,while alkaline conditions were favorable for the adsorption of cationic dyes ST,which was mainly attributed to the fact that PPy exhibited protonization and deprotonization in acidic and alkaline solutions,respectively,thus showing different charge interactions with anionic and cationic dyes.(4)Using the interaction between cellulose and graphene oxide(GO)on the molecular chain scale,MCC/GO composite aerogels with different GO contents were prepared by in-situ physical intercalation.The interaction studies showed that there is a strong hydrogen bond interaction between GO and MCC molecules,thus promoting the exfoliation of GO in the composite aerogels.The microstructure characterization showed that the presence of GO obviously caused the morphology change of MCC/GO composite aerogels,and the degree of change depended on the content of GO.When the GO content is relatively low(less than 3.2 wt%),the three-dimensional(3D)porous structure of MCC/GO composite aerogels is mainly formed by MCC.In the case of relatively high GO content(6.2 and 14 wt%),in addition to the 3D porous structure of MCC,GO also forms a 3D porous structure through the overlap of adjacent GO laminates.The stability test showed that the pure GO aerogels were damaged to different degrees after ultrasound in water,ethanol and cyclohexane,while the MCC/GO composite aerogels showed excellent structural stability in three solvents.Adsorption test showed that compared with pure GO aerogels,the adsorption capacity of the cationic dye MB per unit mass of GO in the composite aerogel is greatly improved,especially when the GO content is low(0.3wt%),the adsorption capacity of the unit mass GO was as high as 2630 mg/g,which is mainly related to the increase of GO exfoliation degree and the morphology of unfolded GO in composite aerogels,that is,more oxygen-containing functional groups on GO participate in the MB adsorption process.(5)The MCC/GNP composite aerogels with highly oriented structure were prepared by directional freezing.Morphology characterization showed that with the increase of GNPs content,the formation of highly oriented structure in the MCC/GNP composite aerogel was more favorable.Furthermore,MCC/GNP/PEG composite phase change materials(PCMs)were prepared by vacuum impregnating polyethylene glycol(PEG)with composite aerogels.This highly anisotropic composite PCMs have high latent heat value(182.6 J/g),high thermal conductivity(1.03 W/m K),excellent encapsulation capability and mechanical stability when the GNPs content is only 1.51 wt %.The results of light-thermal and electric-thermal conversion tests showed that the composite PCMs had excellent solar energy collection/electrical energy conversion,storage and release capability.In addition,the composite PCMs can be used as a temperature protection element in the heating device,which can prevent the rapid rise of temperature in the heating process and keep the temperature at a high level for a long time in the cooling process.Through the research of this thesis,it provides new ideas for the preparation and structural design of new cellulose-based composite PCMs. |
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