The Ambient Pressure Drying Preparation And Properties Research Of Silica Aerogels And Their Composites

Silica aerogel has many excellent properties because of its unique structure,and it has a wide range of application prospects in various technical fields.Therefore,it has attracted more and more attention in recent years.Silica aerogel is a kind of nanoporous structure material with high specific surface area,high porosity,low density,low dielectric constant and low thermal conductivity.However,silica aerogel is often expensive to prepare and have poor stability and mechanical strength.As a result,silica aerogel is difficult to be promoted on a large scale.Currently,silica aerogel is mainly used in military and aviation fields.In order to expand the application of silica aerogels into civil field,this research was mainly to improve the preparation method of silica aerogels to reduce the preparation cost and perfect product performance,and to prepare composite aerogels by doping other materials in order to open up the way for the application of silica aerogel.This article mainly researched the preparation and properties of silica and its composite aerogels,mainly including the following three parts:(1)Preparation and Characterization of Pure Silica AerogelsThe preparation of pure silica aerogels by using sol-gel method,surface modification of trimethylchlorosilane,and ambient pressure drying process were investigated.The product have nanoporous crosslinked network structure,with Si and O as the main components,existing in amorphous state and their surface were replaced by methyl groups after modification.The pure silica aerogels have good thermal stability,high specific surface area of 624.90m2·g-1,pore size around 10 to 20nm,and the porosity is as high as 98%.(2)Preparation and Characterization of Silica Nanofiber-Silica Composite AerogelsBased on the successful preparation of pure silica aerogels,the composite aerogels were further studied.Tetraethyl orthosilicate was used as the silicon source and in-situ synthesized silica nanofibers were used as reinforcing phase.Silica nanofiber-silica composite aerogels were prepared by sol-gel method,surface modification of trimethylchlorosilane and ambient pressure drying.Silica composite aerogels were used to characterize the related structure and properties of composite aerogels.The effect of silica nanofibers on the composite aerogels was studied.The results show that the addition of silica nanofibers can form an effective framework structure,improve the micro-morphology and spatial structure of silica aerogels.Silica nanofiber-silica composite aerogels have good compatibility,dispersion and thermal stability,and maintain a high porosity with specific surface area of 562.50 m2·g-1,pore size of around 10 to 20 nm,and their porosity up to 97%.(3)Preparation,Characterization and Properties of Silica-Titania-Iron Composite AerogelsBased on the above studies,the aerogels of the ternary composite system were further studied and their excellent performance in the catalytic field was verified.Tetraethyl orthosilicate was used as the silicon source,tetrabutyl titanate as the titanium source,and iron nitrate as the iron source.The silica-titania-iron composite aerogels were prepared by sol-gel method and ambient pressure drying.The related structures and properties of composite aerogels were characterized,and their photocatalytic properties were studied.The results showed that the silica-titania-iron composite aerogels were composed of nanoparticles and showed anatase titania crystals with specific surface area of 538.20 m2·g-1,pore size of around 5 to 10 nm,and porosity of 97%.Compared with titanium dioxide,its photocatalytic efficiency has greatly increased.