Investigation of desalination performance of capacitive deionization technology

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2019
Özkul, Selin
Capacitive deionization (CDI) is one of the emerging technologies developed with the purpose of water desalination. CDI technology is based on ion electrosorption at the surface of electrically charged electrode couples that are commonly comprised of porous carbon materials. Along with the continuous increase in the global fresh water demand, CDI technology becomes more prominent as an energy efficient and cost-effective water purification process. In this study, ion removal capacity of the CDI process was investigated under various operational conditions using different carbon based electrodes. For this purpose, carbonaceous supercapacitor electrodes were developed from commercially available, cost-effective activated carbon and graphene materials, and the use of these materials for deionization was explored in detail. The porosity, morphology and chemical nature of the carbonaceous materials were analysed, and it has been found that both materials are porous with different structural properties. Electrochemical properties of the fabricated electrodes were also investigated, and both electrodes showed good electrochemical reaction kinetics and follow electric double layer mechanism during electrosorption process. Furthermore, deionization performances of the fabricated carbonaceous electrodes were evaluated in a laboratory scale CDI unit. The electrosorption behavior of carbonaceous electrodes was analyzed at different electrical potentials and water flow rates, and impact of operating parameters on the sorption capacity was investigated. At a flow rate of 20 ml/min and at a potential of 2.0 V, the maximum electrosorptive capacities of 8.9 μmol/g and 10.7 μmol/g were obtained from activated carbon and graphene electrodes, respectively. In addition, monovalent and divalent ion removal capacities of the fabricated electrodes were determined using solutions with different initial salt concentrations. Graphene-like material with high mesoporosity showed better deionization performance at high concentrations considering removal of both monovalent and divalent ions, yet microporous structured activated carbon reached higher ion removal capacity for monovalent ions at lower salt concentrations.