(458g) Electrokinetic Modeling of Salt Transport and Rejection in Graphene Oxide Nanofiltration Membranes

Graphene oxide (GO)-based membranes have gained tremendous interest in nanofiltration (NF) and reverse osmosis (RO) applications. A major challenge in GO membrane science is to improve their salt rejection in NF and RO processes. Previous researchers have proved that the interlayer spacing between the GO layers as well as the charge density of the GO layers can strongly influence salt rejections from ideal/dilute solutions. However, many practical desalination and dewatering processes operate at much higher concentrations. In this work, our goal is to systematically understand and predict the effect of salts concentration on GO membrane properties by electrokinetic modeling supported by experimental measurements. The correlations between feed concentration, interlayer spacing, and charge density of these GO membranes were determined by single-component salt permeation experiments and ion adsorption models. The modified Donnan steric pore model was then used to model, fit, and predict the salts rejections at different conditions. We then use the transport model investigate in detail the contributions of convection, diffusion, and electro-migration as a function of feed conditions. Finally, the combined effects of initial charge density and interlayer distances on salts rejection are evaluated through the plotting of 2D heat maps. Our study indicates that for neutral pH, under low salt concentrations (~ 0.01 M), modifying the charge density of GO will be more helpful for increasing salt rejections. On the other hand, under high concentrations (above 0.1 M), decreasing the interlayer distance of the GO membranes (i.e., reduction of effective pore size) would be a better strategy. Finally, we show the accurate prediction of binary/multicomponent salt mixture permeation behavior using the model. Overall, this study provides mechanistic insight into salt transport and rejection in GO membranes, and useful guidance for modification of GO membranes in a number of desalination processes.