Ionic Transport Regimes for Nanoscale Transport towards the Development of Low Energy Water Desalination Membranes

Abstract

AbstractNew materials, methods, and membranes are being developed for applications in water purification. One of the model systems that can be used for fundamental studies in nanoscale transport phenomena for new membrane technologies are nanocapillary array membranes (NCAMs). Toward developing more efficient membranes for water desalination, parameters such as the concentration polarization region which are influenced by the unstirred layers, surface properties (e.g., surface charge and surface energy) of the nanocapillaries, and the electric double layer (EDL) which mediates transport across NCAMs must be better understood. In this paper, a series of parametric experiments that were conducted to better understand the relative importance of unstirred layers with respect to the transport across nanocapillaries are described. Bulk salt concentration and potential drop across the NCAMs, were varied in a systematic manner to determine the influence EDL thickness and electromigration on transport regimes for ionic permeation across NCAMs. Based on previously developed methodologies, the experiments reported here were conducted in a permeation cell with an NCAM separating two reservoirs containing potassium phosphate buffer with a concentration range from 200 μM-10 mM. Methylene blue (MB) is used as an organic marker and the transport is quantified by tracking MB concentration in each reservoir with UV/VIS spectroscopy.