Constructing A Two-dimensional Mixed Matrix Membrane Based On Graphene Oxide

In recent years,the shortage of water resources and water pollution have become increasingly prominent.In order to response this challenge,it is urgent to develop efficient and sustainable separation technologies to handle unconventional water sources.Membrane separation technology has become an important method for water treatment because of its low energy consumption and high separation efficiency.With the development of membrane separation technology,it has become an effective way to develop the next generation of high-performance water treatment membrane using two-dimensional nanosheets as building blocks.At present,for water treatment and ion sieving,it has been proved to be feasible to construct water molecule transport and ion sieving channels through the interlayer spacing of two-dimensional materials.It is found that graphene oxide（GO）has great potential in water treatment because of its regular channel structure and abundant oxygen-containing functional groups.However,during the study,it was found that pure GO membrane had some problems such as low mechanical strength,swelling and poor stability in water.So we try to adjust it from different aspects on the basis of graphene oxide in this paper.（1）A sulfonic acid type GO composite membrane（CPSN@GO）was prepared by introducing a cross-linked polystyrene sulfonate networks（CPSN）homogeneously spread in the 2D galleries constructed by GO nanosheets.Since the CPSN@GO composite membrane combine the advantages of regular and ordered ion transfer channels contributed by the 2D GO lamellar assembly structure and rapid ion permeation contributed by the ample ionic groups of cross-linked polystyrene sulfonate.Accordingly,CPSN@GO shows quite high perm-selectivities of 34 and 20 for Na⁺/Mg²⁺and Li⁺/Mg²⁺,the fluxes of the Li⁺and Na⁺can reach 2.58 and 2.6 mol m^-2h^-1 respectively during the electrodialysis process.In addition,the mechanical properties of the composite membrane can be greatly improved,and to a certain extent the shortcomings of GO swelling and instability are improved.This study will provide a general strategy for the development of high-performance two-dimensional ion-sieve membranes.（2）It is planned to use GO as the substrate and introduce pH-responsive molecules between the layers of graphene oxide inspired by the smart response material to regulate the size of the nanochannels.The polyacrylic acid grafted graphene oxide composite membrane（PAA@GO）and polyvinylpyridine grafted graphene oxide composite membrane（P4VP@GO）were constructed through simple free radical polymerization.The molecular chain swells or shrinks and the effective size between layers changes due to the pH’change.The research results show that the response ratio of alkali-responsive PAA@GO membrane can reach 4 under different pH conditions,and the response ratio of acid-responsive P4VP@GO can reach 5.And the composite membrane can effectively control the entry and out of molecules or ions of different diameters,the rejection rate of PAA@GO for p-nitroaniline（NA）molecule is 81.6%under acidic conditions,and can reach 100%under alkaline conditions.In the P4VP@GO composite membrane,the rejection rate of NA molecules under alkaline conditions is 19.5%,while under acidic conditions it reaches 88.9%.In addition,research on the industrial application prospects of pH-responsive membranes show that the membrane has excellent separation potential in acid-base recovery.In particular,the acid dialysis coefficient of P4VP@GO membrane can reach 0.006 m h^-1,and the separation factor can reach 55,providing a reference method for the current acid-base recovery system.The implementation of this subject will provide new ideas for the preparation of smart two-dimensional membranes with pH-regulated nanochannels.