ARTICLE pubs.acs.org/est
Mesoporous Carbon for Capacitive Deionization of Saline Water C. Tsouris,†,* R. Mayes,† J. Kiggans,† K. Sharma,‡ S. Yiacoumi,‡ D. DePaoli,† and S. Dai† † ‡
Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6181, United States Georgia Institute of Technology, Atlanta, Georgia 30332-0373, United States
bS Supporting Information ABSTRACT: Self-assembled mesoporous carbon (MC) materials have been synthesized and tested for application in capacitive deionization (CDI) of saline water. MC was prepared by self-assembly of a triblock copolymer with hydrogen-bonded chains via a phenolic resin, such as resorcinol or phloroglucinol in acidic conditions, followed by carbonization and, in some cases, activation by KOH. Carbon synthesized in this way was ground into powder, from which activated MC sheets were produced. In a variation of this process, after the reaction of triblock copolymer with resorcinol or phloroglucinol, the gel that was formed was used to coat a graphite plate and then carbonized. The coated graphite plate in this case was not activated and was tested to serve as current collector during the CDI process. The performance of these MC materials was compared to that of carbon aerogel for salt concentrations ranging between 1000 ppm and 35,000 ppm. Resorcinol-based MC removed up to 15.2 mg salt per gram of carbon, while carbon aerogel removed 5.8 mg salt per gram of carbon. Phloroglucinol-based MC-coated graphite exhibited the highest ion removal capacity at 21 mg of salt per gram of carbon for 35,000 ppm salt concentration.
’ INTRODUCTION Capacitive deionization (CDI) is being developed as a potential method for removing salts from aqueous solutions. The mechanism of CDI is similar to that of energy storage in supercapacitors. It involves application of an electric field between two electrodes to force ionic species toward oppositely charged electrodes. The ions are held within the electrical double layer (EDL) formed near the electrode surfaces. Electrodes of low electrical resistivity and high surface area contribute to a higher ion removal capacity. This process has several potential advantages over conventional desalination methods including reversibility, operation at low voltages, potential for low energy requirements, and reduction of secondary wastes. CDI has been investigated for the removal of sodium, chloride, and heavy metal ions using carbon aerogels.1 5 The potential for commercial application of CDI as an energy efficient technology for water treatment has been discussed in recent literature.6,7 Because of their high conductivity and high surface area per unit mass, porous, nanostructured carbon aerogels are acceptable materials for CDI. Carbon aerogel has a low electrical resistivity (
