NSF-BSF Application: Selective Transport of Divalent Cations through Polymeric Membranes Using Host-Guest Chemistry

Project Details


In recent decades, membrane filtration processes have emerged as a leading technology in the water sector, mainly for desalination of seawater and brackish water. The most widely used membranes unselectively remove almost all dissolved constituents, including salt. Developing membranes that can selectively separate different dissolved molecules could have great benefits in applications related to water, energy, biotechnology, and chemical processing. For example, in recent years, there has been a growing need for highly selective water treatment processes to recover valuable resources or selectively remove target contaminants. One class of problematic species in brackish water, industrial water, and seawater desalination applications are ions, such as calcium and sulfate that can precipitate as minerals and form scaling layes that block and clog the membrane. Source waters with high concentrations of these ions exhibit high propensity for this hindering phenomenon called inorganic membrane scaling. As more desalinated water are extracted the source water, the salt concentration in the remaining brine rises and the problem is aggravated. Effective strategies for mitigating scaling on membrane surfaces would greatly improve the economics of desalination processes.

The main approach to reduce scale-forming potential mainly include adding chemicals that inhibit the formation of most crystalline scales. However, prolonged addition of chemicals is unsustainable. Other selective processes that could be used to extract scale-forming ions include are often chemical and energy intensive. One of the most common sources of membrane scaling in desalination is calcium sulfate dihydrate (gypsum). The divalent calcium ion have double the electric charge of the monovalent ion sodium, the abundant table salt ion that is the main target of desalination. Therefore, to reduce the potential for gypsum scaling, there is a need for a sustainable technology for selective removal of calcium in the presence of sodium, as well as other smaller ions. The proposed research will overcome the inefficiency and low selectivity of existing processes for scale-forming ion removal by developing a novel membrane with sufficiently high selectivity. Development efforts the will be inspired by the working principles of biological channels, which only permit specific ions to pass through them.

Utilizing the new membrane prior to a conventional desalination process, will allow to extract more freshwater from the saline source and minimize the environmental hazardous brine. This technology would be the first continuous, chemical-free approach for high-precision separation of divalent ions from monovalent ions. This study will also advance our fundamental understanding of selective transport processes by applying a new theoretical approach, which is based on energetics of chemical bonds and rates of chemical reactions between the membrane material and the ions. The insights and design principles established in this study will be relevant for other challenging separations such as the extraction of valuable resources from various waters and wastes.

Effective start/end date1/01/20 → …


  • United States-Israel Binational Science Foundation (BSF)


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