Development of new water resources and sustainable use of existing water sources are increasingly critical due to growing pressure on world water supplies. Highly efficient technologies, such as reverse osmosis exist for performing city-scale seawater desalination, but these require large plants, high applied pressures, and remove all dissolved species. Many other applications demand instead energy-efficient selective removal of hazardous ionic contaminants, a key challenge for next-generation water treatment processes. The emerging electrosorption technology of capacitive deionization (CDI) has been shown to selectively remove particular ions in a competitive ionic environment, a property that could be leveraged to remove harmful ions from water while retaining benign or beneficial species, like calcium and magnesium. The hydrated size of the competing ions, valence, shape, and mobility in solution have all been shown to affect their selective removal.

Despite this promise, intrinsic selectivities in CDI are relatively modest and are often unsuitable for practical use. To address this shortfall, we study the enhancement of ion-ion selectivity via the chemical addition of charged functional groups to electrode surfaces. Using a combined theoretical and experimental approach, we aim to determine the regimes of electrode surface charge and CDI operating parameters that allow for highly-selective removal of targeted ions for a variety of ionic compositions.