Research On Polvamide Nanofiltration Membrane With Cellulose Nanocrvstal Interlayer

Nanofiltration is a type of pressure-driven membrane separation process.Due to its high separation efficiency and low energy consumption,nanofiltration has been widely used in many fields,such as brackish water desalination and drinking water purification.How to promote the permeation and separation performance remains a big challenge in advanced nanofiltration membranes.Researchers develop different methods to fabricate high performance nanofiltration membranes.From the angle of the structure,we fabricate triple-layered composite nanofiltration membranes constructed by interfacial polymerization on a cellulose nanocrystal interlayer supported by microporous substrate.Cellulose nanocrystal plays an important role in the interfacial polymerization and nanofiltration process.One the one hand,the highly hydrophilic interlayer has small pore-size and high porosity to store aqueous diamine monomers at low concentration.Consequently,the polyamide skin layer is thin and has small membrane resistance,which is significant for the high permeate flux.On the other hand,this hydrophilic interlayer also facilitates the water permeation through a "dragging effect".Moreover,the interlayer provides mechanical support for the skin layer,so the microporous membrane can be chosen as the substrate instead of ultrafiltration membranes,which also decreases the membranes resistance.This method is promising for preparing high performance nanofiltration membranes.To investigate the influence of the interlayer properties on nanofiltration membranes structure and performance,we select cellulose nanofibers and imogolite nanotubes as interlayer,respectively.The cellulose nanofibers have large aspect ratio and prefer to be entangled during vacuum filtration.Thus,the interlayer is nonuniform,which results in a skin layer with discontinuous particles after interfacial polymerization.The skin layer is easily damaged during nanofiltration process.Imogolite nanotubes interlayer is smoother and has smaller pore size compared to cellulose nanocrystal interlayer,because of its small diameter and uniform size.However,imogolite nanotubes are less hydrophilic than cellulose nanocrystal and nanofiltration membrane has smooth skin layer but low permeate flux under the same condition.