Fabrication And Performances Of Biomimetic Hollow Carbon Tube Materials

In the field of micro/nano materials,researchers have combined artificial synthetic materials and preparation processes to imitate and replicate natural structures and functions,and have developed several typical structural bionic materials,such as bionic photonic crystals,super-wetting interface materials,and mechanical structural materials,etc.Among them,polar bear hair has received extensive attention and research due to its unique hollow structure and excellent thermal insulation performance.In recent years,a series of porous fibers and fabrics inspired by the structure of polar bear hair has been successfully prepared,but the preparation process is relatively complicated and it is difficult to fabricate macroscopic three-dimensional materials.Therefore,it is still a big challenge to develop a simple synthetic strategy,elaborately tune the microstructure of the material,design and fabricate macroscopic three-dimensional materials,and realize the functionalization and application exploration of the material.This thesis focuses on this point,a simple template-directed hydrothermal synthesis strategy is developed by using tellurium nanowires as a physical template,and the macroscopic biomimetic hollow carbon tube aerogel materials were finally fabricated.Firstly,mimicking the microstructure of polar bear hair,a bionic carbon tube aerogel material similar to polar bear hair is obtained by optimizing the carbon tube wall thickness and porosity.The carbon tube aerogel is ultra-light,hydrophobic,and heat-insulating,and it has superior elasticity and fatigue resistance properties than polar bear hair.Furthermore,the biomimetic dual-function carbon tube composite aerogel was designed and prepared for solar steam generation,and the important role of the carbon tube aerogel thermal insulation layer in improving the solar-thermal conversion efficiency was explored.Finally,a dense multi-node cross-linked hollow carbon fiber block was designed and prepared,the mechanical strength of which was greatly enhanced.The primary research achievements obtained are summarized as follows:1.Inspired by the excellent thermal insulation performance of the hollow structure of polar bear hair,a strategy based on a template-oriented hydrothermal synthesis was developed using tellurium nanowires with a diameter of 35 nm as templates and glucose as a carbon source.Firstly,glucose was hydrolyzed and coated on the surface and junctions of the nanowires and a core-shell fiber hydrogel was formed.After the high-temperature calcination,the nanowire templates were removed,and a hollow carbon tube aerogel material similar to the microstructure of polar bear hair was finally obtained.The shell thickness and the density of the aerogel were changed by simply adjusting the mass of reactants,it was shown that the optimal wall thickness of the carbon layer was 25 nm.At this time,the carbon tube aerogel was light and hydrophobic,and the density was only 9.61 kg m-3,the contact angle was 146°.And the solid content of carbon tube aerogel was low,the porosity was as high as 94.3%,so its thermal conductivity was only 23 mW m-1 K-1 and lower than air.What’s more,carbon tube aerogel showed super-elasticity and fatigue resistance due to the cross-linked carbon tube network framework.The compression recovery speed of carbon tube aerogel was as high as 1434 mm s-1 under the impact of a steel ball,and carbon tube aerogel can keep structure integrity after a million of compressions.Besides,the carbon tube aerogel showed outstanding performance stability with nondegenerate thermal insulation under high humidity and repeated compression,and it can still accurately output the electrical signal in the 100 Hz high-frequency compression cycles.The excellent thermal insulation and mechanical properties of the biomimetic carbon tube aerogel come from its unique hollow carbon tube network structure,which can be used in the field of thermal insulation and piezoresistive devices.2.Based on the superior carbon tube aerogel,biomimetic difunctional carbon-tube-based aerogels were prepared for efficient steam generation.For achieving a dual-use effect of one material,the lightweight and hydrophobic carbon tube aerogel was used directly as a heat insulation layer,and carbon tube aerogel compounded with silica for hydrophilic treatment and then compounded gold nanoparticles for improving the absorption of sunlight to obtain the light absorber layer.The biomimetic difunctional carbon-tube-based aerogels showed over 80%solar-thermal conversion efficiency and good seawater desalination performance.Among them,the carbon tube aerogel insulation layer can effectively resist the thermal transfer from the surface of the light absorber layer to the water.The thermal balance analysis results show that the presence of the carbon tube aerogel insulation layer can reduce the heat conduction loss by about 11%,thereby effectively improving the light-to-heat conversion efficiency.Under 1 sun,the photothermal conversion efficiency of the seawater desalination of biomimetic difunctional carbon-tube-based aerogels device reaches 82.8%,and in the collected freshwater,the concentration of Na+,Mg2+,Ca2+,K+,B3+ions largely reduced to meet drinking water standards.3.Inspired by the hollow structure of polar bear hair and the tube-node structure of bamboos,a dense multi-node cross-linked hollow carbon fiber network structure was designed and prepared,and the mechanical enhancement was realized.During the hydrothermal synthesis process,a suitable concentration of nanowire template can greatly increase the number of nodes and avoid fiber aggregation caused by excessive concentration,thereby hollow carbon fiber materials with high mechanical strength were obtained.Among them,the compressive fracture strength and Young’s modulus of the hollow carbon fiber material were up to 2.6 MPa and 52 MPa,but the density and the thermal conductivity was only 0.061 g cm-3 and 0.068 W m-1 K-1.Compared with ordinary wood,the hollow carbon fiber material had a lower density and better thermal insulation and mechanical properties.To further improve the toughness of the hollow carbon fiber material,the toughness of the composite material was greatly improved after compounding 30%mass fraction of polyurethane,the bending strain at break was increased by two times,and the fracture strength was nearly doubled.The biomimetic hollow carbon fiber material was hydrophobic and oleophilic,can be dried at high temperature and normal pressure after soaking in ethanol,and can be used in engineering structural materials,oil-water separation materials,thermal insulation materials,and other fields.