Fabrication And Functional Applications Of Superelastic Silica Nanofiber Based Aerogels

Silica aerogels with large surface area,small pore size,and high porosity would have broad applications ranging from electronics,sensors,energy to bioengineering.Generally,the silica aerogels are comprising of nanoparticles or nanoparticles/fibers composites,but the aerogels always suffered from the brittleness,the shedding of particles,poor mechanical properties ascribed to the weak interaction with between nanoparticles or nanoparticles and fibers.To thoroughly address these issue,the ceramic microfibers were selected as the building blocks to construct the aerogels via suction filtration,nevertheless such aerogels have a heavy weight and no elasticity.The introducing of nanocarbon or graphene to the fibrous structure could improve the elasticity,but these methodologies impaired the properties of ceramic materials such as high temperature resistance and thermal-insulation properties.Most recently,ceramic nanofiber?ZrO₂,TiO₂,and BaTiO₃?based sponges have been fabricated via solution blow-spinning process using a specially-made cage-like collector.However,the sponges made from such method are fluffy with little resistance to deformation and difficult to control the density,pore structure,and shape.Therefore,construction ceramic aerogels with ultralight density,good structural stability,and elasticity remains an elusive goal as these properties are often mutually exclusive.In this paper,the silica nanofiber based aerogels with ultralow density and superelasticity have been constructed by combining the flexible electrospun silica nanofibers and freeze-shaping technique.The resultant silica nanofiber based aerogels exhibit the integrated properties of ultralow density,superelasticity,and multi-functionalities.The detailed contents are summarized below:?1?We have reported a strategy for rational design and fabricating flexible,hierarchical mesoporous,and robust ZrO₂ nanoparticle-embedded silica nanofibrous membranes for phosphate removal by combining the chitosan dip-coating method with the electrospinning technique.Our approach allows ZrO₂ nanoparticles to be in situ firmly and uniformly anchored onto SiO₂nanofibers by the formed carbon nanolayer on the surface of SiO₂ nanofibers,which could drastically enlarge the specific surface area and porosity of membranes.Therefore,the resultant nanofibrous membranes exhibited a prominent removal efficiency of 85%and excellent adsorption amount of 43.8 mg P g^-1 membranes in 30 min toward phosphates.Furthermore,the removal performance toward different types of phosphates revealed that the resultant membranes also could be used to remove phosphates in detergent and fertilizer water samples.More importantly,the membranes with good flexibility could directly be taken out from solution after use without any post-treatment.?2?We have presented a solvent-free,synergistic assembly strategy for scalable fabricating superelastic,honeycomb structured SiO₂/C nanofibrous aerogels by the combination of sustainable konjac glucomannan?KGM?biomass and the flexible SiO₂ nanofibers.For the first time,the natural KGM was reconstructed into 3D elastic bulk carbonaceous aerogels with tunable densities and desirable shapes on a large scale.Benefiting from the ultralow density(minimum of 0.14 mg cm^-3),super cyclable compressibility,zero Poisson's ratio,good electrical conductivity,and high sensitivity to pressure,the SiO₂/C nanofibrous aerogels can detect dynamic pressure in a wide range?>10 Pa?with a robust sensitivity of 1.02 kPa^-1 in a wide temperature stability from-50 to 200°C with high durability.These attributes enabled us to monitor in real time and in situ real pressure signals such as human blood pulses.We expect that such fascinating CNFAs will open up numerous opportunities for a wide range of applications in future wearable electronics such as health-monitoring devices,human-machine interface devices,nanorobotics,and artificial skins.?3?We have demonstrated that ultralight ceramic-based aerogels can be made superelastic by the combination of hierarchical cellular fibrous architectures and AlBSi bonded SiO₂ nanofibers.With their ultralow density(minimum to 0.15 mg cm^-3),resilient compressibility,zero Poisson's ratio,temperature-invariant superelasticity,low thermal conductivity(minimum to 0.025W m^-1 K^-1),and fire resistance,we anticipate that these exceptional SiO₂/B₂O₃/Al₂O₃ nanofibrous aerogels will open broad technological implications in thermal insulation,catalyst supports,adsorbents,flexible electrical devices,and electromagnetic,energy,acoustic,or vibration damping.Moreover,our discovery also provides the possibility to explore the properties and applications of ceramics in a lightweight,resilient and structurally adaptive form.Furthermore,the basic principles of the preparation and the resilient mechanism of CNFAs were demonstrated;thus,we can expect that,similar to SiO₂ nanofibers,a variety of other ceramic nanofibers could be involved in the SiO₂/B₂O₃/Al₂O₃ nanofibrous aerogels fabrication,offering ample opportunities to develop many new ceramic-based functional aerogels.?4?We have presented a method for creating the recoverable ceramic nanofibrous aerogels made of pure silica nanofibers by assembling the stiff but flexible silica nanofibers into the three-dimensional cellular architecture.The flexible and bendable silica nanofibers endow the as-prepared aerogels with elasticity in drastically contrast to the brittleness nature of ceramic materials.The resultant silica nanofibrous aerogels exhibit the integrated properties of ultralow density(minimum of 0.2 mg cm^-3),complete recovery from large deformation,zero Poisson's ratio,temperature-invariant superelasticity,and fire resistance,all resulting from the synergistic effects of ordered nanofibrous architectures and well-bonded flexible silica nanofibers.The relevance between the mechanical properties of silica nanofiber and silica nanofibrous aerogels have been illustrated to controllable regulating the performance of resultant nanofibrous aerogels.