Tubular ceramic-based multilayer separation membranes using spray layer-by-layer assembly

Abstract

An automatically controlled spray-layer-by-layer (LbL) assembly method was used to build multilayers onto a tubular ceramic macroporous substrate. Poly(ethyleneimine) (PEI) and poly(acrylic acid) (PAA) were alternately sprayed onto a rotating tubular ceramic substrate. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analyses of different locations on the substrate confirmed that a fine coating formed on both the top surface and in the pores of the macroporous ceramic substrate. The substrate pretreatment using water filling greatly influenced the self-assembly process, slowing the penetration of the polyelectrolyte into the substrate pores, resulting in different multilayer morphologies. The effects of the substrate pretreatment, number of bilayers, and the addition of salt into the polyelectrolyte solution on the dye rejection performance were investigated. We found that the substrate pretreatment and the addition of NaCl to the polyelectrolyte solution could change the multilayer structure, in turn affecting the separation performance of the composite membranes. The composite membrane consisting of 5 layers of PEI/PAA had a flux of ∼10.0 kg m⁻² h⁻¹ and a rejection of >99%. Moreover, spray-LbL assembly using different polymer pairs such as poly(diallyldimethylammonium chloride)/poly(styrenesulfonate) (PDDA/PSS) and PEI/TiBisLac/PAA on vertically held tubular Al₂O₃ substrates was also explored. Using these materials led to the formation of different types of polymeric multilayers and in situ nanohybrid multilayers. Our study demonstrates that a multilayer membrane can be successfully prepared on a 3D support by an automated spray system, and can easily be used to rapidly coat large areas.