Preparation, Functionalization And Properties Of Silk Fibroin Nanofiber Aerogel

Silk fibroin nanofibers（SNFs）is a natural fibrous protein-based biopolymer extracted from natural silk.It has good biocompatibility,controllable biodegradability,excellent mechanical properties,and good processability,and has been widely used in the preparation of various functional materials.In recent years,SNF aerogels have high potential in applications such as thermal insulation,filtration,oil-water separation,and medicine due to their unique properties.However,traditional SNFs extraction processes inevitably destroy the natural hierarchical structure and natural characteristics of silk fibers,resulting in low porosity and weak elasticity of the prepared aerogels,severely limiting their function and application.Therefore,this paper first used the urea/hydrochloride guanidine（Urea/GH）deep eutectic solvent（DES）liquid phase peeling strategy to extract multi-scale silk fibroin micro-nanofibers（SMNFs）and studied the effect of DES on the structure and properties of SMNFs and clarified the mechanism of DES liquid phase peeling of silk fibers.Secondly,SMNF aerogels were prepared by cold-induced assembly and vacuum freeze-drying process,and the structure and mechanical properties of SMNF aerogels were systematically studied.The mechanism of the improvement of mechanical properties of SMNF aerogels was analyzed,and the application of SMNF aerogels in air filtration and thermal insulation was explored.Based on this,SMNF/CMC composite aerogels with ordered pores structure were prepared by further regulating the microstructure of SMNF aerogels by adding carboxymethyl cellulose（CMC）.The mechanical strength of SMNF aerogels was enhanced,and poly（methylsilsesquioxane）（PMSQ）and poly（3,4-ethylenedioxythiophene）（PEDOT）were in situ synthesized on the SMNF/CMC composite aerogels as carriers to explore their potential applications as oil-absorbent materials and humidity power generation materials.The specific research content and results are as follows:（1）Extraction of silk fibroin micro-nanofibers using low eutectic solvent liquid phase peeling strategy and its mechanism:Urea/GH DES was used to liquid phase peel silk fibroin（SF）fibers,and the microstructure,chemical structure,crystalline structure,and thermal stability of the extracted SMNFs were characterized.The results showed that the SMNFs extracted by DES consisted of three different diameter scales of SF original fibers（i.e.,tens of nanometers of SNFs,hundreds of nanometers of submicron SF fibers,and microscale ultrafine silk fibroin microfibers（SMFs））.SMNFs and SF fibers have similar chemical structure,crystalline structure,and thermal stability.In addition,SMNFs have good dispersion stability in aqueous solution,which is conducive to the formation of a stable three-dimensional network skeleton structure of the subsequent prepared SMNF aerogels.（2）Preparation of Super-Elastic SMNF Aerogel and Its Air Filtration and Thermal Insulation Properties:Using SMNFs as precursor material,SMNF aerogel was prepared by freeze-induced assembly+vacuum freeze-drying process.The aerogel has a layered porous cell structure,and the cavity wall is composed of multi-scale SMNF tangled and overlapping,which makes the SMNF aerogel has an ultra-low density（as low as 4.71 mg/cm³）.Ultra-high porosity（up to 99.68%）and excellent hyperelasticity（recovery rate of over 80%after 100 repetitions under 60%high strain compression）.Based on the layered and porous microstructure and mechanical properties of SMNF aerogel,it demonstrated excellent filtering ability for high concentrations of PM_2.5（1500μg/m³）and PM₁₀（5500μg/m³）,with a filtration efficiency of over 95%in 15 minutes and good durability.Additionally,SMNF aerogel exhibited an extremely low thermal conductivity coefficient(27 m W·m^-1·K^-1),demonstrating excellent thermal insulation performance,and it maintained high thermal insulation capabilities even after multiple compressions and releases,highlighting its structural stability.（3）Construction of Ordered Pore SMNF/CMC Composite Aerogel and Its Oil Absorption and Humidity Power Generation Performance:In order to enhance the mechanical strength of SMNF aerogel,CMC was added to regulate the microstructure of the SMNF aerogel,and the effect of the amount of CMC on the mechanical properties of SMNF aerogel was systematically studied.The results showed that with the addition of CMC,the SMNF/CMC composite aerogel gradually exhibited a layered and ordered pore structure,which was beneficial to enhance the mechanical properties of the aerogel.When the mass ratio of SMNF to CMC is 7:3,the maximum compressive stress of SMNF/CMCs composite aerogel reaches the maximum value.After 50 cycles of compression under 60%compression strain,the aerogel retains 86.70%of the original maximum compressive stress and 78.72%of the relative height,showing good mechanical elasticity.The unique ordered pore structure of SMNF/CMCs composite aerogel improves the ability of liquid absorption and ion transfer.For example,the silane-modified SMNF/CMC composite aerogel sheet is super hydrophobic,,and could be used as an adsorbent material for oil pollution in water,with a adsorption rate of 53.43-142.20 g/g for various oil agents and repeatable use performance.The PEDOT-functionalized SMNF/CMC composite aerogel achieved conductivity and had the ability to generate electricity under humid conditions,with the output voltage related to the depth of immersion in the solution.Furthermore,adding inorganic salts to the water solution can improve its saltwater power performance,and the functionalized aerogel showed an output voltage of up to 1120 m V in saturated Na Cl solution,making it promising for monitoring water level warning.