Tuning the RO membranes using the spin-assisted layer by layer assembly of polyelectrolytes

Abstract

Polyelectrolyte multilayer films are currently used to modify the permeation and rejection properties of thin-film composite membranes (TFC). In this paper, response surface methodology was used to study the effect and synergies between interactive parameters essential for modification of the TFC membrane. TFC membranes were prepared using m-phenylenediamine and trimesoyl chloride and modified by spin-assisted layer-by-layer (LbL) technique using polyethyleneimine (PEI) and polyallylamine hydrochloride as the deposition polyelectrolytes. The Box–Behnken design of experiment (DOE) was applied to investigate the effect of preparation conditions (number of deposited layers, pH, the concentration of the polyelectrolyte solutions) on the performance of the modified reverse osmosis (RO) membranes. It was found that under saline feed conditions, higher permeate flux favors higher pH and higher PEI concentration, while salt rejection favors a similar concentration of both polyelectrolytes. In addition, the PEI concentration was found to have a stronger effect on the permeate flux than that of the number of bilayers since it enhanced the hydrophilic functional groups on the membrane surface. Analysis of variance results indicated that the developed models adequately represent the relationship between the studied variables. Optimization of the preparation conditions revealed that both polyelectrolytes must be used at their maximum concentration at a pH of 7.8 with 50 bilayers of the coating. The confirmation run showed a close correlation between the prediction using the DOE and the actual experimental data. This study demonstrated the potential application of DOE to the optimization of LbL RO membrane preparation conditions.