Preparation And Transport Intensification Of Hydrophilic/Hydrophobic Heterostructured Lamellar Nanofiltration Membrane

With the development of the chemical industry,the excessive discharge of organic solvent is an impossible burden on environment and also leads to the waste of resources.Therefore,it is urgent to develop an environmental and efficient technology to recycle the organic solvent.Organic solvent nanofiltration?OSN?,as a new membrane separation technology,has attracted wide attention due to its unique separation characteristics.The laminar membrane,as a rising star in the OSN membrane,has attracted great attention arisen from the rapid molecular transport and precise size sieving.And a variety of lamellar membranes have been developed such as MXene,transition metal disulfides and metal organic frameworks etc.To further enhance the nanofiltration performance of lamellar membrane,the construction of physical structure and the design of micro-chemical environment have open an avenue for the lamellar membrane.In this study,we are committed to the controllable construction of transport channel.The hydrophobic hydroxyl-terminated polydimethylsiloxane?PDMS?,hydrophilic graphene oxide?GO?nanosheets,and hydrophobic reduced graphene oxide?RGO?nanosheets are utilized as the materials to fabricate the lamellar membrane.The hydrophilic/hydrophobic heterostructure is constructed on the surface and interlayer channel of lamellar membrane,respectively,via electrostatic atomization to enhance the transport of solvent molecule.Such heterostructure subtly synergize the superiorities of two materials with reversed hydrophilicity/hydrophobicity,opening an avenue to the fabrication of new OSN membrane.The details and conclusions are shown below:?1?Construction of heterostructured surface.Inspired by the hierarchical structures of Namib Desert beetle's back,GO nanosheets were flat deposited on nylon support via electrostatic atomization,contriving highly ordered sheet laminates and hence regular interlayer channels.Thus,hydrophobic PDMS clusters were patterned the surface of hydrophilic GO laminate,the lamellar membrane with heterostructured surface?PDMS@GO?was obtained followed by the thermo-crosslinking between PDMS and GO.The hydrophobic PDMS clusters enhance the molecular dissolution of non-polar solvent while the hydrophilic interlayer channels endow non-polar solvents with ultra-low barrier diffusion.In addition,the highly ordered sheet stacking strengthens the structural stability of lamellar membrane attributed to multi-site interactions between nanosheets.Compared with the GO membrane,the heterostructured lamellar membrane exhibits highly enhanced molecular permeation?over 7 times?while fully retaining the precise molecular rejection?1.4 nm?.Besides,the permeance is essentially maintained?<6%?during the 48-h operation.?2?Construction of heterostructured interlayer channel.The hydrophilic GO and hydrophobic RGO nanosheets were used to construct a regular laminate with alternating nanosheets,realizing the controllable construction of heterostructured interlayer channel.Concretely,such channel with hydrophilic region on the top and hydrophobic region on the bottom effectively control the micro-chemical environment of interlayer channel,intensifying the molecular transport of solvent with large dipole moment?such as acetonitrile?.Together with severe limitation of transport for water molecules,the lamellar membrane with heterostructured interlayer channel achieves the molecular separation of acetonitrile and water.Compared with GO membrane,the mixture solvent permeance of acetonitrile and water?1:1 w/w?were increased to 63.9 L m^-2 h^-1 bar^-1,with an increase of 153.7%.And a high acetonitrile/water selectivity?3.2?was obtained.