Fabrication Of Graphene-based Aerogels By Emulsion Method And Their Adsorption Properties

Graphene-based aerogel is a new three-dimensional carbon material constructed with two-dimensional graphene flake layers as skeleton material.It possesses the characteristics of high conductivity,heat resistance and hydrophobicity of graphene nanoscale,and is also endowed with super light density,large specific surface area and shows great potential in many fields,such as sensors,supercapacitors,adsorption materials and so on.The key to the industrialization of graphene-based aerogel is how to control the pore structure,porosity and density under mild conditions,and enhance the mechanical strength to meet the industrial requirements.In this paper,Pickering emulsion was used as a soft template.The construction and regulation of graphene-based aerogels were realized by changing the oil/water ratio,the type of oil phase and the doping of modified multi-walled carbon nanotube?MMWNTs?,and then the adsorption mechanism was investigated.Graphene aerogel?emGA?was fabricated with GO stabilized emulsions as soft template via hydrothermal process.GO/MMWNTs were dispersed in water and mixed with toluene to form homogeneous emulsion,then a porous graphene-MMWNTs composites?MCG?were prepared through hydrothermal reaction.The results of characterization show that the aerogels contained abundant micron sized pores.It was observed that with the increase of oil/water ratio,the emGA density reduced,while the porosity and specific surface area increased.The pore size of MCG can be effectively controlled by changing the oil/water ratio of the emulsion.The emGA with toluene as oil phase exhibited excellent extrusion elasticity in both radial and axial direction.The adsorption properties of emGA were studied by using organic solvents and oil in water as adsorption objects.The former mainly investigated factors affecting the adsorption capacity and its recycle performance.The results showed that the adsorption capacity of aerogels was positively correlated with the solvent density and oil/water ratio,and the cyclic regeneration of aerogels could be achieved by thermal desorption and mechanical extrusion.The latter focused on the adsorption mechanism of the oil in water and the related factors,experimental results show that adsorption process conforms to psudo-second-order?PSO?kinetic model,and the adsorption process can be divided into three phases.The adsorption activation energy is 35.07 kJ?mol^-1,belonging to physical adsorption.The adsorption isotherms were fitted with Freundlich model.The analyzing results show that the adsorption rates of straight-chain alkanes were faster than cycloalkanes and aromatic hydrocarbons with similar carbon numbers.Lower density of emGA and higher temperature favored the increase of adsorption rate.EmGA and MCG were used as adsorbents to investigate the adsorption properties of graphene aerogel on methylene blue?MB?.The adsorption kinetics of emGA fit the PSO model.The larger the specific surface area of emGA,the higher its adsorption capacity on MB.The process of MCG adsorption on MB was related to its pore size.The smaller the pore size,the slower the adsorption rate.After 5 times of cycles of adsorption-desorption operation,the adsorption capacity of MCG decreased slightly.The adsorption thermodynamic parameters showed that the adsorption process is spontaneous endothermic and belongs to physical adsorption.