(731a) Understanding the Salt Transport Properties of Graphene Oxide Membranes: Permeation Measurements and Electrokinetic Modeling

Graphene oxide (GO)-based membranes have gained tremendous interest in nanofiltration (NF) and reverse osmosis (RO) applications. A major challenge in GO membranes is to improve their salt rejection in NF and RO processes. Previous researchers 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 and extreme pH conditions. In this work, our goal is twofold: to systematically measure the effect of salts concentration (0.01 – 0.5 M) and pH (3-13) on GO membrane properties particularly in extreme conditions, and to understand and predict these properties by electrokinetic modeling. The correlations between feed concentration/pH, interlayer spacing, and charge density of these GO membranes were determined by tracer 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 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 “heatmaps”. Our study indicates 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 examine the possibility of accurate prediction of multicomponent salt behavior using single-component data. 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.