| Nanofibers aerogels have been widely used in adsorption,biomedicine,thermal insulation,flame retardancy,energy storage,sound insulation,and catalysis,due to their low density,high porosity,high specific surface area,and low thermal conductivity.Anisotropy means that the chemical and physical properties of matter show different characteristics in different directions,and the anisotropic structure endows aerogels with new properties and broadens their application range.Directional freezing is a particularly versatile technique as a means of realizing anisotropic structural materials.Based on this,in this paper,nanocellulose aerogels with the anisotropic structure were prepared by directional freezing technology,which was applied to the fields of thermal insulation and oil-water separation.（1）Preparation of superamphiphobic cellulose nanofibrils（CNF）aerogels with anisotropic structure.Using CNF as raw material,different ratios of tert-butanol/water solution（3～5%）as the solvent,CNF aerogel was prepared by directional freezing with special freezing method,and CNF aerogel was modified by chemical vapor deposition（CVD）.The results show that the contact angle of the directionally frozen aerogels is higher than that of the randomly frozen aerogels.At the same time,with the increase of tert-butanol content,the pores present a finer arrangement and a rougher structure,and the lyophobicity of the aerogel increases.When the content of tert-butanol was 5%,the contact angles of directionally frozen CNF aerogels with water,glycerol,ethylene glycol,and castor oil were 161°,158°,156°,and 151°,respectively.Superamphiphobic CNF aerogel with self-cleaning properties.As a material with self-cleaning functions,it is of great significance in gas sensors,catalysis,and supercapacitors.（2）High-strength and superamphiphobic composite aerogels prepared based on directional freezing for thermal insulation and flame retardant applications.A composite aerogel was developed by directional freezing and CVD modification using chitosan（CS）and montmorillonite（MMT）as thermal insulation raw materials and CNF as reinforcing filler.The intercalation between CS molecular chains and MMT endows the aerogel with excellent mechanical properties,and the Schiff base reaction between glutaraldehyde（GA）and CS can effectively improve the mechanical properties of aerogels..Due to the anisotropic structure,the axial Young’s modulus is as high as 630 KPa and the radial thermal conductivity is as low as 32m W m-1K-1.At the same time,aerogels showed 43%of the high limit oxygen index（LOI）value.In addition,the contact angle between composite aerogels and various oils and water reaches 150degrees or more by CVD modification,realizes the self-cleaning performance,and the heat insulation performance under different humidity conditions is basically unaffected.The composite aerogel is expected to have potential applications in housing,interior decoration,aviation,and other fields.（3）The ultra-light bio-based aerogels are prepared based on bidirectional freezing has excellent cyclic oil absorption performance.Using CS and CNF as raw materials,a highly directional wave structure and a chemical vapor deposition modification on the surface were prepared by bidirectional freezing.A super light density and shape memory aerogel was prepared for oil-water separation.While expounding the importance of bidirectional freezing structure for shape memory,the effects of different raw material ratios,aerogel density and cross-linking methods on the shape memory and mechanical properties of aerogels were studied.After 50cycles of compression release test,aerogels still maintained more than 88%of their original compressive strength,with a high recovery rate of 96.6%,showing excellent recoverability.The adsorption capacity of various organic solvents reached above 100 g g-1,and the adsorption capacity of trichloromethane was as high as 232 g g-1.At the same time,it had excellent recycling performance.After 10 simple and convenient adsorption extrusion cycles,the retention rate of aerogels reached 87.5%,and the recycling performance was excellent.This super light aerogel with excellent shape memory has potential application prospects in the field of oil-water separation. |
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