Catalytic Capacitive Deionization for Adsorption and Reduction of Aqueous Nitrate

Capacitive deionization (CDI) is an environmental remediation technology that can remove aqueous ionic contaminants, but a major drawback of this process is the production of concentrated waste streams that necessitate further processing. We report a novel approach termed catalytic capacitive deionization (CCDI) that combines selective heterogeneous catalysis with CDI to significantly reduce undesired waste products. In CCDI, porous electrodes containing catalytic nanoparticles are used to electrostatically adsorb and degrade ionic contaminants to less toxic byproducts. We demonstrate CCDI through the removal and reduction of nitrate in water toward innocuous nitrogen gas rather than thermodynamically favorable ammonium. A 50 mg-N/L nitrate was continuously fed to the CCDI reactor at 1 mL/min and adsorbed and treated through 20-min adsorption/catalytic cycles, resulting in an effluent containing 2 mg-N/L nitrate and trace amounts of byproducts, below maximum concentration levels defined for drinking purposes. At a cell potential of 1.5 V, the CCDI system removed 92% of the nitrate in the feed, and 91% of the adsorbed nitrate was selectively transformed to produce innocuous N-2. This work demonstrates that CCDI can potentially be used as a novel approach to treat a wide range of aqueous ionic contaminants, significantly advancing the next generation of CDI systems.