Preparation Of Ultralight And Compressible Graphene Aerogel By Reduction Self-assembly Method

Graphene aerogels have a continuous three-dimensional network structure with large surface area,excellent electrical conductivity and thermal conductivity.They are widely used in supercapacitors,adsorption,catalysis and electromagnetic shielding.However,graphene aerogels are easily broken after being subjected to force,which limits their application in various fields.In order to improve the compressibility of graphene aerogels,the reduction and self-assembly method was used to prepare ultra light compressible graphene aerogels.(1)The effects of microcrystalline graphite and flake graphite on compressibility of graphene aerogels were compared.Flake graphite is used as the raw material for subsequent preparation because of its large size and narrow distribution,which can obtain uniform and continuous graphene aerogels during the self-assembly process.L-ascorbic acid is used as the reductant for subsequent preparation because of its convenience and acidity,which can simplify the reduction process.(2)The effects of reductant dosage,temperature and time on the structure and composition of three-dimensional graphene were studied.As the dosage of reductant increased,the density and volume shrinkage of graphene aerogels increased rapidly.The minimum values were 12.99 mg/cm3 and 84.60%,respectively.When the mass ratio of reductant and graphene oxide reached 3,it tended to be smooth.The quality of graphene lamellae first increases and then decreases with the increase of reductant dosage.When the mass ratio is 3,ID/IG reaches the lowest value of 1.298.With the increase of reduction temperature,the continuity of graphene three-dimentsional mesh was improved,and complete graphene three-dimensional structure was obtained at 80 C.The quality of graphene lamellae first decreased and then increased with the increase of reduction temperature,which is the worst at 70℃ the ID/IG was 1.291.With the increase of reduction time,the density of graphene aerogels increased steadily,the volume shrinkage rapidly increased until 120 min,and the defects of graphene lamellae decreased.ID/IG reached a minimum value of 1.197 at 160 min.The reduction degree of graphene increased rapidly but did not change significantly after 120 minutes,when the C/O atomic ratio fluctuated around 5.45.(3)The effect of ammonia concentration on the structure and composition of graphene aerogels before freeze drying was studied.The compressibility of graphene aerogels comes from the multiple washing and ammonia treatment of graphene hydrogels.As the concentration of ammonia increased,the density and volume shrinkage of graphene aerogels increased rapidly.When the concentration reached 25wt%,the aerogels completely lost the structure of aerogels.The resistivity decreases by 20 times in the range of 5-10 wt%，and then fluctuates near 10Ω·cm.With 10 mL graphene oxide(3 mg/mL)as raw material,when the amount of reducing agent is 90 mg,the reduction temperature is 90℃,the reduction time is 120 min and the concentration of ammonia is 5wt%,the obtained graphene aerogel density is 6.82 mg/cm3,and the sample is very sensitive to the compression load response.Therefore,a super light and compressible graphene aerogel can be obtained.(4)The formation process of three-dimensional structure during graphene self-assembly was analyzed,and a stacking model of graphene sheets was proposed.In the reduction process,graphene oxide lamellae attract each other due to the reduction of repulsion force,stacking to form a convex sheet structure,while completing the connection to form a three-dimensional structure.As the reduction degree increases,the mesh walls attract and stack each other to form a new stage of mesh,resulting in the planar contraction of the sheet structure and folding.The process of mesh attraction is repeated to form a multi-level and multi-scale three-dimensional spatial structure until the reduction limit of the system is reached.