Nano-enhanced membranes for desalination and water reuse

Abstract

Membrane technology has promising applications to address the water-energy nexus. Pressure-driven membrane processes, e.g., reverse osmosis and nanofiltration, are widely used for desalination and water reuse in countries and regions threatened by water scarcity. Other membrane processes, such as fuel cells and reverse electrodialysis, have been used for clean energy applications. Nanotechnology and biotechnology can play an important role to enhance membrane performance, leading to better membrane permeance, selectivity, and/or antifouling performance. This presentation highlights some of the recent developments in nano- and bio-enhanced membranes. The first part of the presentation focuses on the origin and control of nanoscale surface roughness of reverse osmosis membranes. The polyamide rejection layer of reverse osmosis membranes has a ridge-and-valley morphology that contains numerous encapsulated nanovoids of several tens to hundreds of nanometers.1 We show that these nanovoids are caused by the interfacial degassing of CO2 nanobubbles during the polymerization of polyamide at an interface of aqueous and organic solutions.1 This mechanistic understanding led to various strategies for the control of membrane surface morphology, which provides useful tools for membrane performance optimization.1,2 The second part of the presentation focuses on the development of novel nanocomposite membranes. We report the use of aquaporins, i.e., water channel proteins, for enhancing membrane permeance and selectivity. In addition, the inclusion of interlayers of nanomaterials in composite membranes were shown to achieve an order of magnitude enhancement in water permeance, accompanied with improved selectivity against a wide range of contaminants.3 The potential of these next generation membranes will be evaluated in the context of desalination and water reuse.