Structural Construction And Application Of Silica/Graphene Composite Aerogels

It is generally known that silica aerogel is the lightest solid material with low density,high porosity,high dispersion and high specific surface area,which exhibits unique mechanical,acoustic,thermal characteristics.Pure silica aerogel fabricated by atmospheric drying tends to break,due to its high brittleness and poor toughness.When silica aerogel is used alone,there will be a series of problems such as low strength of skeleton,poor mechanical properties and uneven pore size distribution which cannot meet the requirements of people.The work focuses on fabricating silica/graphene composite aerogels with good bulk and mechanical properties by atmospheric pressure drying(APD),providing more possibilities for its applications.This thesis mainly includes the following three parts.(1)Preparation and characterization of low density silica aerogel.The effects of pH,modifier trimethylchlorosilane(TMCS)and tetraethyl orthosilicate(TEOS)concentration on structure and properties were investigated by single factor variable method to determine the optimal preparation process.When the pH value is 7,the volume ratio of TEOS to TMCS is1:3.2,and the concentration ratio of TEOS to absolute ethanol is 4:7,the obtained silica aerogel exhibit high specific surface area 789.349 m~2/g)and high mass retention rate(88%)at790?.(2)Preparation and characterization of silica/graphene oxide composite aerogel.The influence of the graphene oxide amount on the structure and properties of the composite aerogel was investigated.When 4 mg of graphene oxide was added to the dilute solution of 5mL of silicon precursor,the overall performance was the best.The block ability of the sample was obviously improved,the specific surface area was as high as 855.057 m~2/g,the pore diameter was 9.805 nm,and the hydrophobic angle was 124±1o.After the high temperature treatment at 790?,the mass retention rate was about 93%.(3)Preparation and characterization of silica/reduced graphene oxide composite aerogel.Firstly,the block-shaped and highly elastic reduced graphene oxide sponge was prepared by chemical reduction method.The composite of silica and reduced graphene oxide sponge reinforced framework was realized by impregnation method,obtaining good mechanical properties.During the preparation process of reduced graphene oxide sponge,the effects of reduction temperature,reduction time and amount of reducing agent on the properties of reduced graphene oxide sponge were investigated.When the reduction temperature is 90?,the reduction time is 4h,and the mass ratio of graphene oxide to reducing agent is 1:20,the prepared reduced graphene oxide sponge has the best performance.During the composite process,the influence of the silica precursor concentration on the properties of the composite aerogel was mainly investigated.When the silica precursor concentration is greater than a certain degree,the composite aerogel is damaged during APD.When the ratio of TEOS to absolute ethanol is 4:7,a whole composite aerogel can be obtained.When the cylindrical composite aerogel with a diameter of 1cm could sustain 50 g mass,there is no change in shape.The enhancement of the reduced graphene oxide sponge skeleton was further proved by stress-strain test and SEM image analysis of the samples before and after compression.When the sample is applied to oil-water separation,it can adsorb 6-7 times of its own mass,and the adsorption capacity does not decrease significantly when it is repeated ten times.