Study On Oil/Water Emulsions Separation Properties Of Graphene-based Membranes

Everything grows with water.Water resources is a valuable natural resource that is of great significance to human survival and development.However,with the continuous development of society,the problems of water consumption and pollution become more and more serious.The use and development of water resources has become a social focus and an important research topic.Oil pollution accounts for a large part of many forms of water pollution.Crude oil spills,industrial emissions,and daily activities of human all produce a variety of oil to water.Traditional oil-water separation methods often have problems such as low efficiency,incomplete cleaning,high energy consumption,and poor recyclability.Some even cause secondary pollution.Emulsions,as a thermodynamically stable,transparent monodisperse system formed by water droplets in oil(W/O)or oil droplets in water(O/W),is more difficult to separate.Therefore,the development of new high-performance oil-water separation materials is imminent for human life and production.In this paper,graphene and related composite membrane materials are used to prepare high-performance emulsion separation and filtration membranes by vacuum filtration because of their excellent physical and chemical properties such as ultra-high specific surface area.Compared with traditional filter membranes,graphene-based membranes have the characteristics of high flux,high efficiency,and good reusability.In order to extend the application range of graphene-based membranes so that they are not restricted by the substrate,this paper also explores a method of transferring graphene oxide membranes prepared by vacuum filtration from the substrate.Moreover,for the purpose of reducing the cost,ordinary paper tissue was used as the material to prepare a very low-cost paper tissue-based composite for both highly efficient oil absorption and water-in-oil emulsion separation.The main research results obtained are summarized as follows:1.Preparation of graphene oxide/Si O₂ composite membrane.Through the introduction of hydrophilic nano Si O₂ particles,the layer modification of graphene oxide was achieved,which not only increased the surface roughness but also increased the roughness of each layer and thus significantly improved hydrophilicity.The inter-layer space is enlarged ten times to make it have higher water permeability and lower water resistance,which makes it easier to obtain higher emulsion separation flux.Therefore,it solves the problems of low throughput and high energy consumption of the traditional emulsion separation membrane,achieving a filtration flux of up to 4550 L m^-2 h^-1 bar^-1,which is 2 to 3 orders of magnitude higher than the filtration flux of pure GO membranes.At the same time,the efficiency of filtering different oil-in-water microemulsions is above 99%,so the preparation of GO/Si O₂composite membranes has great potential for wastewater treatment,especially for difficult emulsion separation applications.2.Realizing of liquid phase separation of graphene oxide membrane.The problem that the high-quality GO membrane prepared by vacuum filtration cannot be separated from the substrate is further solved,and the process is quite fast,simple,and repeatable.The structure of the obtained GO film is very flat,and the thickness can be precisely controlled with thinnest thickness can reach 45 nm.The liquid phase separation method is easy to operate,the process is environmentally friendly,and can be completed in 1 minute.The 45 nm film has a transmittance of about 90%at 550 nm,which proves that it has excellent optical properties.Secondly,GO can be reduced by various methods such as high temperature(800°C)to obtain high-quality graphene films.In addition,the GO film separated from the filter paper can also be easily transferred to various substrates,such as PET,silica,silicon wafers,flat glass,etc.Because of its ultra-flat surface structure,it can often be spontaneously bonded to the substrate without adhesive,which is beneficial to further applications.3.In order to further reduce costs as well as to realize the water-in-oil emulsions separation,we explored the use of ordinary paper tissue as the material to prepare dual-use paper for oil adsorption and emulsion filtration.The whole preparation method is simple,fast and inexpensive.On the one hand,it can be used as an adsorption material.Although many three-dimensional oil-absorbing materials can absorb a large amount of oil,most of them can not completely remove trace oils in water due to their weak capillary effect.As a result,they cannot achieve a"deep cleansing"of water or the separation of water/oil emulsions.In contrast,the PDMS/Si O₂ composite paper proposed in this chapter can remove 99.9%of oil under the same conditions,and the absorption time has been shortened to one fifth.On the other hand,as a filtration membrane capable of separating water-in-oil emulsion without external pressure.At the same time,it solves the problems of low throughput and high energy consumption that traditional filtration membranes face.Its filtration flux can reach(2000 L m^-2 h^-1),and the separation efficiency is as high as 99.4%.In conclusion,this paper solves the problem of low filtration flux of traditional graphene-based membranes,realizing high-performance oil-water emulsions separation.It has the advantages of low cost,simple,high filtration flux and efficiency,and good reusability,leading to huge potential of commercial applications.Moreover solution-assisted method was successfully used to separate and transfer graphene oxide membranes of different thicknesses prepared by vacuum filtration.Getting rid of the limitations of the filter paper substrate results to further expand the applications of graphene-based membranes especially the ultrathin membranes prepared by vaccum filtration which have super-flat surface structure.Meanwhile,the low-cost"filter paper tissue"was prepared for the separation of water-in-oil emulsion,making emulsion separation and filtration as comprehensively as possible.