Layer-by-Layer Assembly of Inorganic Nanosheets and Polyelectrolytes for Reverse Osmosis Composite Membranes

In this study, we introduce a layer-by-layer (LbL) assembly method to prepare a reverse osmosis (RO) desalination membrane that consists of a hybrid combination of [polyelectrolyte (PE)/montmorillonite (MTM)](n) layers. First, adopting poly(allylamine hydrochloride) (PAH) for a PE layer, an RO test showed that the permeate flux of water through (PAH/MTM)(n) multilayer-coated membranes decreased from similar to 25.5 to similar to 8.3 L.m(-2).h(-1) with the increased bilayer number from n = 9 to n = 18. At the same time, the corresponding ion rejection with respect to NaCl is increased from similar to 30 to similar to 81%. Despite the increased ion rejection performance, (PAH/MTM)(n) membranes exhibit a poor chlorine resistance, as frequently observed in commercial polyamide-based RO membranes. In our previous study, it was noted that the RO membranes, prepared just from the PE multilayers (i.e., [PAH/poly(acrylic acid) (PAA)](n) layers), showed a marked chlorine tolerance, but concomitantly very low permeate flux (similar to 4-5 L.m(-2).h(-1)). Considering the significant drawback in each case (poor chlorine tolerance for (PAH/MTM)(n) layers and low permeate flux for (PAH/PAA)(n) layers), we proposed to combine the layer constituents primarily by inserting PAH/PAA layers between two adjacent PAH/MTM layers. Indeed, the flux is maintained at similar to 7.5 +/- 0.5 L.m(-2).h(-1), comparable to commercial membranes, while the salt rejection ability is as high as similar to 75 +/- 2.5% and the stability against the chlorine attack is well preserved with similar to 74 +/- 5.0% ion rejection after the NaOCl treatment.