Layer-by-layer self-assembly of polycation/GO/OCNTs nanofiltration membrane with enhanced stability and flux

The permeation flux of pure graphene oxide (GO) membrane is low because of its narrow and variable interlayer spacing. To overcome this drawback, a multilayer membrane with sandwich structure was assembled alternately by GO and oxidized carbon nanotubes (OCNTs) on a polyacrylonitrile substrate via a layer-by-layer self-assembly technology. The role of polydimethyl diallyl ammonium chloride (PDDA) was to connect GO and OCNTs. The PDDA/GO/OCNTs multilayers (M (n) ) consisting of 3, 5, 7 and 9 bilayers were deposited. The performance of nanofiltration membranes can be optimized by adjusting the number of sandwich layers. As the assembled layers increased, obvious fluctuation and fold forms of membrane increased, which was conducive to increase separation performance of composite membrane. Rejection rate for Alphaurine A and water flux of M (7) were 94.42% and 28.53 L m(-2) h(-1), respectively, at 3 bar. Meanwhile, M (7) had higher flux compared with the reported literature in which rejection also reached up to 90%. Rejection rate of M (3), M (5), M (7) and M (9) for Alphaurine A remained 50.45, 87.7, 94.5 and 97.1%, respectively, after the 12-h filtration test. Thus, we thought that composite membrane with sandwich structure via layer-by-layer self-assembly technology of GO and OCNTs under the effect of PDDA had excellent stability and high flux.