Ion rejection properties of NF membranes with inhomogeneous fixed charge distributions are investigated theoretically. It is shown that the occurrence of spatial inhomogeneities in the fixed charge concentration may lead to an enhancement of the salt rejection with respect to a homogeneously charged membrane. Moreover, membranes with appropriate bipolar charge distributions can lead to similar rejections for both 2-1 and 1-2 asymmetric electrolytes. These performances cannot be achieved with homogeneously charged membranes since the Donnan theory predicts that the membrane strongly rejects electrolytes with divalent coions but is much more permeable to electrolytes with divalent counterions. These findings suggest that designing advanced membranes with controlled distribution of surface groups could be of great interest for desalination and water treatment.
Journal: TechConnect Briefs
Volume: Technical Proceedings of the 2010 Clean Technology Conference and Trade Show
Published: June 21, 2010
Pages: 346 - 349
Industry sector: Energy & Sustainability
Topic: Water Technologies