Construction Of Flat And Tubular Multilayer Membranes Using Spray Self-assembly System And Their Separation Performance

In recent years, molecular self-assembly techniques have been widely used tocreate uniform films with nanometer control. In particular, the layer-by-layer (LbL)assembly technique has proven to be a versatile tool for the creation of new densecomposite membranes. However, the classical dipping-LbL method has low preparingefficiency, long production cycle and difficult to industrial amplification. It needs tobe urgently exploited rapid self-assembly technique. Construction of flat and tubularmultilayer membranes using spray self-assembly system and their separationperformance was presented in this article, which could rapidly assemblepolyelectrolyte multilayers on to porous supporting membranes and imporve theefficiency.The construction of flat multilayer membranes using spray self-assemblysystem was built first, the compounds polyacrylic acid (PAA) and poly(ethyleneimine)(PEI), used as a model polyelectrolyte pair, were alternately sprayed on to apolyacrylonitrile (PAN) ultrafiltration membrane and succeed in making themultilayer membrane. In addition, the process times were dramatically decreased, byas much as80folds, when compared with classical dip-LbL methods. Scanningelectron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) analysesand Zeta potential were used in tracking the growing up of multilayer membranes.The pervaporation (PV) dehydration experiments proved that, the polyelectrolytemultilayer membranes obtained from20bilayers had a flux of264g/h·m2and aseparation factor of423(feed solution95.0wt%ethanol-water,65℃). The separationfactor could be further increased to3781with a permeate flux of180g/h·m2when thedeposition was increased to30bilayers.Benefit from the past experiences of spraying layer-by-layer technique on flatsheet membranes, a three dimensional (3D) tubular composite membrane wassuccessfully prepared. By using the fully automated system capable of sprayingpoly(ethyleneimine)/poly(acrylic acid)(PEI/PAA), poly(diallyldimethylammoniumchloride)/poly(styrenesulfonate)(PDDA/PSS) and PEI/TiBisLac/PAA solutions ontovertically held tubular Al2O3substrates leads to the formation of nanometer-sizedfilms. The composite membranes were evaluated in dye purification of dye/water system. SEM images and EDX analysis indicate that the atomization process producesa fine coating on the macroporous ceramic substrate, dramatically changed themorphology of the membrane surface and top alumina layer. The effects of dry andwater filled ceramic substrates, number of layer pairs, additive salt in polyelectrolytesolution, in-suit growth of nanoparticles and membrane stability were investigated. Itwas found that the addition of NaCl in polyelectrolyte solution and pre-treatment ofsubstrate can change film structure and affect the separation performance of thecomposite membranes. The rejection increased largely with the layer pairs, while theflux dropped down step by step. The composite membrane deposited by5layer pairsof PEI/PAA showed a fux of about10.0kg/h·m2and a rejection over99%. Therefore,it is a versatile and highly efficient system for manufacturing composite multilayermembranes for many separation applications.