Ion selectivity in capacitive deionization with functionalized electrode: Theory and experimental validation

Journal Article · Mon Nov 05 00:00:00 EST 2018 · Water Research. X

DOI:https://doi.org/10.1016/j.wroa.2018.100008· OSTI ID:1512611

Oyarzun, Diego I. ^[1]; Hemmatifar, Ali  ^[1]; Palko, James W. ^[2]; Stadermann, Michael ^[3]; Santiago, Juan G. ^[1]

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1. Stanford Univ., CA (United States). Dept. of Mechanical Engineering
2. Univ. of California, Merced, CA (United States). Dept. of Mechanical Engineering
3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Capacitive deionization (CDI) is a promising technique for salt removal and may have potential for highly selective removal of ion species. In this work, we take advantage of functional groups usually used with ionic exchange resins and apply these to CDI. To this end, we functionalize activated carbon with a quaternary amines surfactant and use this surface to selectively and passively (no applied field) trap nitrate ions. We then set the cell voltage to a constant value to regenerate these electrodes, resulting in an inverted capacitive deionization (i-CDI) operation. Unlike resins, we avoid use of concentrated chemicals for regeneration. We measure the selectivity of nitrate versus chloride ions as a function of regeneration voltage and initial chloride concentration. We experimentally demonstrate up to about 6.5-fold (observable) selectivity in a cycle with a regeneration voltage of 0.4 V. We also demonstrate a novel multi-pass, air-flush i-CDI operation to selectively enrich nitrate with high water recovery. We further present a dynamic, multi-species electrosorption and equilibrium solution-to-surface chemical reaction model and validate the model with detailed measurements. Our i-CDI system exhibits higher nitrate selectivity at lower voltages; making it possible to reduce NaNO₃ concentrations from ~170 ppm to below the limit of maximum allowed values for nitrate in drinking water of about 50 ppm NaNO₃.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); CONICYT-BECAS CHILE
• Grant/Contract Number: AC52-07NA27344
• OSTI ID: 1512611
• Report Number(s): LLNL-JRNL-773303; 965471
• Journal Information: Water Research. X, Vol. 1, Issue C; ISSN 2589-9147
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY