Fabrication And Application Of Nanocellulose Based Composite Conductive Aerogel

As the most abundant natural polymer,cellulose and its derivative nanocrystals have received considerable attention.Cellulose–based composite aerogel is a typical three–dimensional cellulose product with unique structural features,such as a three–dimensional cross–linked network,hierarchical pore structure,high porosity,large surface area,low density,low thermal conductivity and abundant surface groups.However,it is difficult for nanocellulose to form an ideal conductive aerogel structure without crosslinking agent and composite conductive materials.The addition of a crosslinking agent leads to an increase in reaction steps and side reactions are unavoidable,improve the chemical reaction barrier and leading to the defects of aggregation and discontinuity of conductive materials.In addition,it would be the most ideal solution to overcome the above–mentioned problems to obtain intrinsically conductive nano–cellulose crystals through the controllable chemical structure transformation on the nano surface.This thesis takes biomass–ginger fiber as a starting point,combined with the new strategy of mixed acid Fisher esterification to give it a high aspect ratio and rich carboxyl groups,constructing a green and sustainable whole cellulose nanofiber(CNF)without crosslinking agent.Furthermore,based on CNF self–crosslinking aerogel,flexible supercapacitors and sensors were designed with conductive polymer supramolecular composite structure and nanocarbon material covalent interconnection structure.Finally,a new confined dehydration carbonization reaction path was proposed.The intrinsically conductive CNFene and its derived graphene topology were obtained,and the all–cellulose intrinsically conductive aerogel was successfully constructed.The specific research content is as follows:1.Extraction of ginger silk CNF and its self–crosslinking aerogel construction:Firstly,carboxylated CNF with high aspect ratio from waste ginger fiber was extracted.These CNFs extracted from waste ginger fiber had abundant carboxyl functional groups and high aspect ratio of 144,CNF were physically cross–linked into an ultra–lightweight and strong aerogel through strong heterogeneous nano–adhesive force(hydrogen bonding).This process did not require any external chemical modification.This CNF self–crosslinking aerogel had recoverable high compressibility and can withstand a maximum compressive stress of 99.5 k Pa at a low density(20.3 mg/cm~3).In addition,the network capture and bridging mechanism of carboxylated CNF to nanoparticles and molecules had been observed,as well as the chemical recombination characteristics in line with pseudo second–order adsorption kinetics.By controlling the types of acids and the ratio of mixed acids,the changes in the morphology and surface chemical structure of biomass CNF were investigated,and the influence of the morphology and surface groups on the subsequent compound chemical reaction kinetics was analyzed to guide the next step of compound preparation.2.The construction and application of CNF/polyaniline(PANI)supramolecular composite conductive aerogel:The supramolecules were assembled through the double hydrogen bond interaction of the high aspect ratio carboxylated CNF and PANI to obtain a nano–scale supramolecular fibers uniformly distributed.The composite conductive supramolecule solved the problem of the discontinuous conductive polymer network and mechanical fragility in the gel matrix caused by the delocalized?electrons of the conjugated conductive polymer skeleton,and imparted conductivity to the CNF aerogel.Supramolecular aerogel(SA)had mechanical flexibility,shape recovery ability and porous network microstructure,which solved the problem of poor electrolyte diffusion encountered in the deposition of conductive polymer supercapacitor devices and slurry dipping methods.The SA–based flexible all–solid–state supercapacitor had a high–quality specific capacitance of 291.01 F/g,and the SA–based flexible sensor had a lower limit of multiple gas monitoring as low as 10 ppm and human pulse monitoring capabilities.By controlling the ratio of CNF and PANI,investigate the supramolecular assembly effect of CNF and PANI under the guidance of double hydrogen bonds,and then analyzed the electrochemical and sensor response performance of supramolecular composite conductive fibers,revealing the capacitive behavior of supramolecular composite aerogels and sensing response mechanism.3.Preparation and application of CNF–multi–walled carbon nanotubes(MWCNT)covalently interconnected conductive aerogels:carboxylated CNF and aminated MWCNT were covalently interconnected by dehydration condensation to prepare The CNF–MWCNT covalently interconnected fiber with a chain–ring structure,which solved the problem of MWCNT aerogel forming and phase separation/aggregation during the compounding process,and gave CNF–based aerogel conductivity.Covalently interconnected aerogels(CA)had mechanical resilience and folded hierarchical porous structure that promoted CNF to wrap around MWCNT to form a continuous uniform network,which made it have high compression resistance up to 269.02 k Pa.CA–based flexible all–solid supercapacitors had a high–quality specific capacitance of 114.8 F/g,a high capacitance retention rate of 94.78%and a coulombic efficiency of 100%.The CA–based flexible sensor had the ability to distinguish different pressures and had high cyclic response stability.By controlling the chemical reaction environment of CNF and MWCNT,the reaction efficiency of this biomimetic covalent bonding strategy in acidity,alkalinity and neutrality was investigated,and then the electrochemical and sensing properties of biomimetic covalent conductive fibers were analyzed.Furthermore,the electrochemical and sensing properties of the covalently interconnected conductive fibers were analyzed,and the capacitive behavior and sensing response mechanism of the covalently interconnected conductive aerogel were revealed.4.Preparation and application of intrinsically conductive CNFene aerogel by confined reaction:Based on an expandable laboratory reaction environment at room temperature and pressure,a method based on the hydration of proton acids to generate covalent bonds was found to emit high heat and hydrated H ion work together to obtain conductive CNFene new material.Which also used the Brnsted acid and the by–product organic acid as the catalyst to form graphene nanoshell by dehydration carbonization(DC)on the confined nano surface of CNF.The conductivity was as high as 1.0099 S/cm.This method did not relied on the high–energy–consuming pyrolysis process of high–temperature graphitization of cellulose above 800 ? any more,and broke through the conventional structural properties of nano–cellulose itself that cannot conduct electricity.The micro–morphology transformation from CNF to CNFene and the transformation of surface chemical structure were observed.According to various characterization and analysis methods,the formation mechanism of CNFene graphene nanoshell and the transformation of surface chemical states were verified.The versatility of the bio–source material limited confined DC method to prepare intrinsic conductive nano–cellulose materials,and electrochemical characterization has confirmed the excellent conductivity of multi–source CNFene.Further,its aerogels capacitance capacity higher than the previous biomass carbon(235.8 F/g).In a word,this thesis was based on biomass CNF and adopted a new mixed acid strategy to obtain a high aspect ratio carboxylated CNF aerogel,and then CNF was composited with conductive polymer and nano–carbon material to prepare conductive aerogel finally explored a brand–new confined DC method and successfully extracted the intrinsic conductive CNFene of graphene nanoshell with its own chemical structure transformation,completing the breakthrough of cellulose from an insulator to a good conductor.Among them,by controlling variables such as composite particles,composite ratio,reaction p H environment,reaction auxiliary particles,reaction temperature and reaction time,it was verified that CNF/conductive polymer supramolecular aerogels and CNF–nanocarbon materials covalently interconnected aerogel had applied potential for supercapacitors and sensors.This novelty method realized the nano–scale precise control of the conversion of the chemical structure of the CNF surface layer,completed the reaction mechanism theory of intrinsically conductive CNFene and a comprehensive analysis of its physical and chemical properties.This doctoral dissertation presents a comprehensive exploration,characterization,analysis and discussion on the extraction of biomass nanocellulose,the preparation of nanocellulose in conductive composite,the discovery of intrinsic conductive nanocellulose,and the construction of cellulose–based conductive aerogels.Each chapter contains a large number of comparisons and supplements with similar cutting–edge research,hoping to provide more ideas and theoretical basis for the research field of new generation nanocellulose and aerogels.