Ionic Liquid Assisted Preparation Of Biomass-based Composite Materials And Their Applications

With the constant progress of human history,the environmental pollution and collapse have been continuing as a leading crisis of modern society.Developing and exploiting environmentally friendly renewable resources have risen as one of the most important solutions to this crisis.Biomass is a family of earth-abundant and natural renewable polymers,with a variety of useful advantages like diverse and green sources,good renewability and biodegradability,cheap and easy accessibility,and environmental friendliness.In this thesis,renewable biomass is employed as starting materials for the production of a novel series of functional materials,where green and eco-friendly ionic liquids(IL)are utilized as auxiliary solvent.This thesis project not only provides new ideas and methods for the development and value-added utilization of biomass,but also offers some theoretical and experimental supports for its practical application.Below is a concise summary of the specific achievements in this thesis project.(1)Via introducing reversible hydrogen bonds and ionic bonds into biomass-based polymeric materials,a biomass-based ion gel is prepared with enhanced mechanical strength and self-healing capability.By using sustainable cellulose nanocrystals(CNCs)and ionic liquid(rather than commonly used water)as model biomass-based materials and solvent,respectively,reversible hydrogen bonds and ionic bonds can be incorporated into biomass-based polymeric materials,producing a novel triple network of ion gel with high mechanical strength and remarkable self-healing capability.By virtue of graphene oxide(GO)and sustainable CNCs that feature structural enhancement capability,as-obtained 1-butyl-3-methylimidazolium hydrogen sulfate(BmimHSO4)-c ion gel delivers enhanced mechanical performance,including good tensile strengths(up to 15.9 MPa),extraordinary elongation rate(610%),and marked toughness(53.8 KJ/m3).Besides,the(BmimHSO4)-c ion gel also exhibits outstanding self-healing capability,which should be attributed to the strong electrostatic interactions between the IL cations(Bmim+)and hydroxyl(OH)groups of poly(vinyl alcohol)(PVA),as well as the extensive hydrogen-bonds among the ion gel.A selfhealing process is documented on the mechanically damaged ion gel in air without any external stimuli.(2)In order to extend the application scenarios of biomass-based ion gels,we improve the ionic conductivity of aforementioned ion gel,paving the way for its application in the field of supercapacitors(SC).Regenerated cellulose nanoparticles(as model biomass-based materials)and IL are used in tandem for the synthesis of highperformance solid-state electrolyte for SC use.Specifically,PVA is used as polymer matrix,while an IL 1-butyl-3-methylimidazolium trifluoromethansulfonate(BmimCF3SO3),graphene oxide and regenerated cellulose nanoparticles are introduced as auxiliary solvent,ionic conducting promoter,and performance regulator,respectively,for facile construction of a doped ion gel.A significantly decreased charge-transfer resistance is witnessed in this doped ion gel,where the homogenous distribution of the regenerated cellulose nanoparticles and graphene oxides renders the ion gel with stable and ordered ion and electron transfer,respectively,thus vastly lowering the charge transfer resistance.The cellulose-based gel electrolyte delivers good SC performance,where a capacity retention of～80%and a charge/discharge efficiency of 98%are recorded after 10,000 cycles.The favorable SC performance is attributed to the improved ionic conductivity,good compatibility with carbon electrodes,and enhanced stability featured by the as-prepared ion gel.Due to its easy preparation and simple components,the ion gel-based electrolyte is facilely scalable,cost-effective,safe,and nontoxic,adding to its acceptance in diverse application senarios in the field of energy storage and delivery.(3)In addition to the reversible hydrogen bonds and ionic bonds,dynamically reversible covalent bonds and metal coordination bonds are effective in enhancing the mechanical and self-healing performance of biomass-based ion gel.In order to extent the application scenarios of various biomass-based materials,a facile strategy is developed based on ubiquitous reversible acylhydrazone bonds among an eco-friendly biomass-based material,polysaccharide,for the construction of self-healing ion gel.After selected oxidation,the polysaccharide can establish reversible acylhydrazone bonds with polyacrylamide,granting as-formed ion gel with fast self-healing capability,where the resultant crack can be recovered within minutes after cutting.It also features good adhesion property and easy modulation capability in terms of gel morphology.which predict its application as durable solid electrolyte in supercapacitors.In addition to aforementioned acylhydrazone bonds,metal coordination bonds are established in the ion gel via mixing Fe3O4 with gel precursors,giving rise to OSA-PAM-Fe3O4-CNCs ion gel with instant self-healing capability and magnetic response.(4)Besides the mechanical,electrochemical,magnetic and self-healing properties,other useful materials performance like photoluminescence can be conjugated into the biomass-based gels via as-developed IL assisted method.A series of strongly luminescent Au nanoclusters(NCs)are prepared,by using a naturally occurring tripeptide glutathione(GSH)as protecting ligands and IL as emission regulators.IL1Au-GSH NCs prepared with EmimCF3SO3(IL1)shows good stability and can be well dispersed in water.Under the excitation wavelength of～410 nm,it shows a strong orange emission peak at-610 nm,which can be attributed to the aggregation induced emission(AIE)mechanism made possible by the electrostatic interactions between IL and Au NCs.Its emission intensity is significantly enhanced by a factor of over two,in comparison to that of pristine Au-GSH NCs without any IL.The emission features of IL1-Au-GSH NCs show varied responses to metal cations(e.g.,Cu2+,Sn2+and Fe3+),which can be used for accurately probing multiple metal cations.In addition,IL2(EmimAcO)is used for preparing IL2-Au-GSH NCs,which show wide-spectrum emission in the entire visible regime.As-prepared IL2-Au-GSH NCs can be utilized as color-switch materials in white light emitting diode(WLED)devices.Moreover,by adding model biomass-based materials,chitosan,into IL2-Au-GSH NCs,the photoluminescent emission intensity and efficacy can be vastly enhanced by the AIE mechanism,where a state-of-the-art photoluminescence quantum yield of 33.71%can be achieved.