Developing Ion Electroadsorption Stereoselectivity, by Pore Size Adjustment with Chemical Vapor Deposition onto Active Carbon Fiber Electrodes. Case of Ca2+/Na+ Separation in Wat

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• 作者：Eran Avraham ; Bouhadana Yaniv ; Abraham Soffer ; Doron Aurbach
• 刊名：Journal of Physical Chemistry C
• 出版年：2008
• 出版时间：May 15, 2008
• 年：2008
• 卷：112
• 期：19
• 页码：7385 - 7389
• 全文大小：150K
• 年卷期：v.112,no.19(May 15, 2008)
• ISSN：1932-7455

文摘

By using carbon chemical vapor deposition (CVD) onto active porous carbon fibers, we were able to reducethe pore size of the active carbon to obtain selective carbon molecular sieves (CMS) of variable properties.The pore size of these carbons was characterized by the adsorption of molecules of different dimensions(molecular probe adsorption) from the gas phase. By manipulating the several experimental parameters ofthe CVD process, the pore size of the CMS could be finely tuned to fall between sizes of alkaline earthcations (Ca²⁺; Mg²⁺, 6-7 Å in diameter), and the much smaller size of hydrated monovalent cations (4 Å indiameter). This was proven by voltammetric measurements of the pore-tailored carbon electrodes in thecorresponding salt solutions, which also provided a measure of the differential capacity of the electrical doublelayer (EDL) vs the potential (e.g., at potentials negative to the potential of the zero charge, the EDL capacitywas very small for CaCl₂ and MgCl₂ solutions, while it was high for NaCl solutions). The CVD processapplied herein did not significantly reduce the specific surface area and the pore volume of the carbons. Thisimplies that the carbon deposits are only superficial and that the pore blocking effect takes place only at thepore mouth. Hence, the adsorption processes related to these carbons involve surface barrier mechanisms.The importance of the selectivity thus obtained relates to a possible use of these carbon electrodes inelectrochemical water desalination processes. By using these carbons as electrodes in capacitive waterdeionization processes, it is possible to selectively remove Na⁺ cations, leaving Ca²⁺ and Mg²⁺ ions (whichare important nutrients) in the treated water.