Study On Graphene Oxide Membrane With Cationic Concentration Controlling Interlayer Spacings And Its Application In Ions Separation

As an efficient and fast separation method,membrane technology has wide applications in different fields.The graphene oxide membrane has become one of the most important membrane materials recently due to its adjustable layer spacing.In addition,graphene oxide membrane is also characterized by ultra-thin,energy saving and high flow rate,which has important research value in the fields of ion,molecular screening and seawater desalination.An important means to achieve ion and molecular screening is to regulate the distance between graphene oxide sheets.This can change the distance between lamella is both opportunity and challenge,changing the layer spacing can meet different screen size between ions and molecules,but at the same time,duing to swelling problem of graphene oxide membrane in aqueous solution,makes it to remain in the aqueous solution layer spacing is small enough to meet small ion intercept,screening,is still a huge challenge.Although many attempts have been made to adjust and control the gap between graphene oxide layers in small sizes,this progress has not been significant,which greatly limits the use of graphene oxide membranes.In this paper,we explored a new method to control the graphene oxide layer spacing,that is,to regulate the graphene oxide layer spacing by changing the cationic concentration based on the hydration cationic-?action.X-ray diffraction?XRD?experiments showed that the layer spacing of graphene oxide membranes decreased with the increase of cationic concentration.Among them,the layer spacing of graphene oxide membranes controlled by the highest concentration of 1.5 M K⁺decreased by 2.1?compared with the natural state of graphene oxide membranes in aqueous solution,showing a significant reduction.Ultraviolet absorption spectroscopy?UV?experiments show that the effect of decreasing layer spacing with increasing concentration is the result of enhanced interaction between high concentration cations and graphene oxide sheets.Further experiments on ion permeation with cationic-controlled membranes of different concentrations showed that the permeation rate of Mg²⁺ions decreases with the increase of cationic concentration,that is,decreases with the decrease of film spacing.Among them,the permeation rate of Mg²⁺on the 1.5 M K⁺controlled graphene oxide membrane was 1/45 of that on the uncontrolled membrane,indicating that the interception effect of Mg²⁺on the control layer spacing with high concentration of K⁺ions was significant.Furthermore,we selected different ions?Na⁺,Li⁺,etc.?as control ions and osmotic ions respectively,proving the universality of this effect.In addition,in order to further study the practical application of this cationic concentration effect,the mixed ions of different components were separated by 1.5 M high concentration K⁺controlled layer spacing go membrane,and the comparative effect of the membrane without cationic control layer spacing was tested.The final results showed that,compared with graphene oxide membranes without cationic control layer spacing,graphene oxide membranes with high concentration of cationic control layer spacing had a significant effect on ion separation,especially for Na⁺/Mg²⁺separation,and the separation coefficient increased from 5.2 to 30.6 for films without cationic control layer spacing.These studies have shown that not only the type of cation,but also the concentration of the cation plays a crucial role in the regulation of graphene oxide membrane spacing in the theory of hydrated cationic-?control of graphene oxide membrane.This discovery broadens the scope of cationic regulation of graphene oxide membrane layer spacing,enabling graphenen oxide membrane to meet a wider range of applications.