Properties And Preparation Of Graphene/ZIF-8 Composite Aerogels

Graphene aerogel refers to the three-dimensional porous network structure with graphene as the main body,which has the nanostructures of graphene and the macroscopic structure of aerogel,and has strong mechanical strength,electron conductivity and mass transfer rate.In addition,the porous network structure has also a large specific surface area?specific surface area of up to 400 m2 g-1?and porosity?porosity up to 99.8%?.So that it has a very wide range of applications,in the adsorption,catalysis,energy storage,electrochemical and other fields.ZIF-8?dimethyl imidazole zinc salt?is a metal skeleton material with a zeolite skeleton structure in which the transition metal is divalent Zn²⁺,2-methylimidazole as an organic linker.The bond length of the M-Im-M unit in the zeolite imidazole ester framework material is longer than that of the Si-O-Si unit in the conventional zeolite,which makes the ZIFs material not only have high porosity,large specific surface area and structure adjustable,but have the high stability of inorganic zeolite.Therefore,ZIFs materials have the potential application in many fields such as gas storage and separation,heterogeneous catalysis,chemical sensors,biomedical imaging and drug delivery.In this paper,the grapheme/ZIF-8 hybrid aerogels were prepared by two-step reduction strategy and layer-by-layer of assembly.The pore structure,gas adsorption properties and mechanical properties of the hybrid aerogels were studied.The carbon nanocomposite porous carbon material was obtained by carbonization at high temperature.The porous structure and the capacitance properties of nitrogen-doped porous carbon were studied.In the aqueous solution,the reaction time was controlled at 95 ?,the ascorbic acid was used to chemically reduce and the graphene hydrogel was prepared,and then the aqueous solution was replaced with methanol solution.The layer-by-layer of assembly was used to prepare the grapheme/ZIF-8 hybrid aerogels?named GZAn,n = 2,4,6,8,and 10?,compared with graphene aerogels,or ZIF-8,GZAn with micropores and mesopores in macroporous pores of multi-layered pore structure,have superior CO₂ adsorption properties,and the compression mechanical properties over graphene aerogels.The CO₂ adsorption capacity of GZA8 was 0.99 mmol g-1 under the conditions of 298 K and 1atm,higher than that of graphene aerogels?0.38 mmol g-1?or ZIF-8 crystals?0.7 mmol g-1?under the same conditions.The nitrogen-doped porous carbon?GZA-T,T=600,700,and 800 ??with different pore structure were prepared by regulating the high temperature annealing temperature and time of GZA8 hybrid aerogel.The solid state supercapacitor was assembled and the capacitance performance of the electrode material was tested in alkaline electrolyte.The maximum specific capacitance of GZA8-800 at 1 A g-1 is 74 F g-1,and the best retained stability is 92% when the current density is 1 A g-1 after 1000 cycles of charge and discharge.GZA8-600,rate capacity of the best performance,from 0.5 A g-1 to 6 A g-1 of the current density,the capacitance is 56% of the initial capacitance.