电容去离子化

电容去离子化（英语：Capacitive de-ionization，简称CDI），是一项应运于去除水中盐分的新型技术。它可以被广泛运用于海水淡化、工农业用水除盐和生活用水除盐。

电容去离子的基本原理

电容去离子的基本思想是通过施加静电场强制离子向带有相反电荷的电极处移动，因此英文称之为capacitive deionization（CDI）。由于碳材料，如活性碳和碳气凝胶等制成的电极，不仅导电性能良好，而且具有很大的比表面积。若将两片活性碳材料分别作为电容器阴阳两级并在两电极之间施加一定的直流电压便会形成一个静电场。置于静电场中碳电极会在其与电解质溶液界面处产生很强的双电层。双电层能吸附并储存大量的电解质离子，并储存一定的能量。一旦除去电场，吸引的离子被释放到本体溶液中，溶液中的浓度升高。这一过程也称为“充电富集”。此种原理也被大量应用在超级电容器和电容盐度梯度发电（capacitive blue energy）中。
和传统的水溶液去离子方法相比，电容去离子具有几方面重要的优势。例如，离子交换是目前工业上从水溶液中去除阴阳离子，包括重金属和放射性同位素的主要手段，但这一过程产生大量的腐蚀性二次废水，必须经过再生装置处理。而电容去离子与离子交换不同，系统的再生不需要使用任何酸、碱和盐溶液，只是通过电极的放电完成，因此不会有额外的废物产生，也就没有污染；同蒸发这种热过程相比，电容去离子具有很高的能量利用率；和电渗析和反渗透相比，该方法还具有操作简便的优势。另外，从地下水中选择性去除Cr（VI）的初步实验表明，对水中某些微量杂质的选择性处理也是有可能实现的。
因为具有能量利用率高，污染小，易操作等优点，电容去离子可以应用在很多方面，包括家庭和工业用水软化、废水净化、海水脱盐、水溶性的放射性废物处理、核能电厂废水处理、半导体加工中高纯水的制备和农业灌溉用水的除盐等。为了尽可能的提高电容去离子化的除盐效率，我们还可以在碳电极表面附着上一层离子交换膜，也就是在阳极上加阴离子选择性渗透膜，在阴极上加阳离子选择性渗透膜，离子交换膜可以阻挡与之同性离子进入碳电极，由此改良双电层内的被吸附离子分布结构，从而吸附更多的离子（图1）。

参考文献

1. G.W. Murphy and D.D. Caudle (1967). “Mathematical theory of electrochemical demineralization in flowing systems,” Electrochim. Acta 12: 1655-1664.

2. A.M. Johnson and J. Newman (1971). “Desalting by means of porous carbon electrodes,” J. Electrochem. Soc. 118: 510-517.

3. Y. Oren and A. Soffer (1978). “Electrochemical Parametric Pumping,” J. Electrochem. Soc. 125: 869-875.

4. J.C. Farmer et al. (1996). “Capacitive Deionization of NaCI and NaNO3 Solutions with Carbon Aerogel Electrodes,” J. Electrochem. Soc. 143: 159-169.

5. C.J. Gabelich et al. (2002). “Electrosorption of Inorganic Salts from Aqueous Solution Using Carbon Aerogels,” Env. Sci. & Techn. 36: 3010-3019.

6. M.D. Andelman (2002). "Charge barrier flow-through capacitor," CA Patent 2444390.

7. T.J. Welgemoed and C.F. Schutte (2005). " Capacitive Deionization Technology: An alternative desalination solution," Desalination 183: 327-340.

8. J.-B. Lee et al. (2006). "Desalination of a thermal power plant wastewater by membrane capacitive deionization," Desalination 196: 125-134.

9. Y. Oren, (2008). "Capacitive deionization (CDI) for desalination and water treatment — past, present and future (a review)," Desalination 228: 10-29.

10. H. Li et al. (2008). "Electrosorptive desalination by carbon nanotubes and nanofibres electrodes and ion-exchange membranes," Water Research 42: 4923-4928.

11. P. Xu et al. (2008). “Treatment of brackish produced water using carbon aerogel-based capacitive deionization technology,” Water Research 42: 2605-2617.

12. P.M. Biesheuvel (2009). "Thermodynamic cycle analysis for capacitive deionization," J. Colloid Interface Sci. 332: 258-264.

13. P.M. Biesheuvel et al. (2009). “Dynamic adsorption/desorption process model for capacitive deionization," J. Phys. Chem. C 113: 5636-5640.

14. R. Zhao et al. (2010). "Charge efficiency: A functional tool to probe the double-layer structure inside of porous electrodes and application in the modeling of capacitive deionization," J. Phys. Chem. Lett. 1: 205-210.

15. Y. Bouhadana et al. (2010). “Several Basic and Practical Aspects Related to Electrochemical Deionization of Water,” AIChE J. 56: 779-789.

16. M.A. Anderson et al. (2010). “Capacitive deionization as an electrochemical means of saving energy and delivering clean water. Comparison to present desalination practices: Will it compete?,” Electrochim. Acta 55: 3845-3856.

17. P.M. Biesheuvel and A. van der Wal (2010). “Membrane capacitive deionization,” J. Membrane Sci. 346: 256-262.

18. Y.-J. Kim and J.-H. Choi (2010). “Improvement of desalination efficiency in capacitive deionization using a carbon electrode coated with an ion-exchange polymer,” Water Research 44: 990-996.