Design,Fabrication And Performances Of 3D Phenolic Resin-based Aerogels And The Derived Carbon Aerogels

As known as the "frozen smoke",aerogels are the lightest solid in the word.They have been attracted great interest due to the unique physicochemical properties.As the fast developing,more and more new aerogels with excellent performances come into views,such as carbon-nanotubes(CNT)aerogels,graphene aerogels and silicon aerogels,and display promising applications in environment,energy storage,sense and industrial fields.However,aerogels cannot be wildly used in the society due to the complex synthesis procedure and high cost.Thus,it is a key step in the wide usage of aerogels to develop a kind of aerogel which can be fabricated easily by the cheap raw materials.Phenolic resins,kinds of traditional inexpensive industrial raw materials with excellent mechanical performance,thermal stability,low smoke release and high char yield,are very promising precursors to make novel aerogels.In this dissertation,we focus our research interest on the phenolic resins and the derived carbon materials.We firstly summarized the progress on the preparation strategies of low dimensional phenolic resin-based nanomaterials.Then we particularly highlighted the progress on the assembly methods of macroscopic 3D phenolic aerogels,and also highlighted the progress on the applications of phenolic resin-based materials and the derived carbon materials in all walks of life.Based on this background,we aim to develop a novel phenolic aerogels.To satisfy different application requirements,we develop several novel phenolic resin-based aerogels by designing the microstructures in microscale and compositing various nanomaterials.Then we explore their applications in energy storage,environments and fire-resistant and thermal-insulated materials.The main achievements can be summarized as follows:1.We report a general and straightforward route to scale-up synthesis of a family of phenolic resin gels under mild conditions,especially phenol-formaldehyde resin(PFR)by using chitosan as 3D soft template which plays a key role in fabricating the gels with tunable microstructures.Negative charged phenolic monomers are attracted on the surface of the positive charged chitosan networks due to the electrostatic interaction.As the polymerization proceeding,the generated phenolic resin deposits on chitosan networks and finally form the novel phenolic nanowires aerogels.Chitosan templated route is a general method to synthesize various phenolic resin aerogels,including phenol-formaldehyde resin(PFR)aerogel,resorcinol-formaldehyde resin(RFR)aerogel and aminophenol-formaldehyde resin(AFR)aerogels.Owing to its low-cost characteristic and universality,this synthetic route provides a benchmark for scale-up synthesis of porous phenolic and other similar resin gels with great potential applications in the future.2.On the basis of the first work,we further make an activated phenolic resin-derived hard carbon aerogels by combining the 3D soft-templating and the ion-catalyst effect.We prepare the PFR/Fe3+ composite aerogel by the chitosan templating method and meanwhile taking the advantage of the chelation effect of phenol and Fe3+.The chelation effect ensures the homogeneous dispersion of Fe in the whole monolith by bring the Fe3+ into every chain-segment of PFR.During the high temperature,the catalytic graphitization effect of Fe activates the inherent disordered PFR-derived hard carbon into a modified three-dimensionally interconnected carbon network embedded with hydrogen-rich,ordered microstructures of expanded nanographites and carbon micropores.The structural merits of the carbon offer chances to achieve lithium/sodium storage performance far beyond that possible with the conventional carbon anode materials.We also discussed the microstructure change and the formation mechanism of the modified carbon.3.As a further exploration of new composite materials by the 3D soft template,we also developed a novel PFR/SiO2 aerogel composed of binary networks by combing the chitosan templated method and the nanoscaled phase-separation.As the polymerization of phenolic resin and the simultaneous hydrolysis of the silica source TEOS,the generated both negative charged oligomers are adsorbed on the positive charged chitosan networks.Subsequently,the organic polymer phase and the inorganic phase induce the phase separation in nanoscale.The obtained PFR/SiO2 aerogels can be used as novel fire-resistant and thermal-insulated materials,which show very low thermal conductivity and fire resistance.1 cm this composite aerogel can resist high temperature(1300 ?)flame for 30 min,meanwhile the temperature of the back side is lower than 300 ?.This composite aerogels with the binary network structure provide a new concept for the design of novel fire-resistant and thermal-insulated materials.4.We also developed a direct route to phenolic resin-derived robust carbon aerogels by salt-templating.Phenolic resin is polymerized under hypersaline condition,such as ZnC12.Salt has a great influence on the microstructures of the obtained phenolic resin,resulting in a black stiff monolith instead of the original yellow monolith.The black monolith is porous,contrasting with the inherently dense and nonporous structure of the original phenolic resin.Due to the robust microstructure,special drying process is unnecessary.After the simple drying,the monolith can convert into a foam-like carbon aerogel by direct carbonization.The salt ZnCl2 plays a key role in the forming of the carbon aerogel,serving as dehydration agent,foaming agent,and porogen.This strategy provide us a direct route to carbon aerogels without special drying,greatly reducing the cost.The carbon aerogels show very promising potential in the separation/extraction of organic pollutants and for energy storage.