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Study and Preparation of the Modified Nanostructure Carbon Electrode for Capacitive Deionization (CDI) Process

Talebi, Majid | 2021

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 54516 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Ahadian, Mohammad Mahdi; Shahrokhian, Saeed
  7. Abstract:
  8. Nowadays capacitive deionization (CDI) has attracted a lot of attention for water treatment. CDI is an emerging water treatment technology that uses electrophoretic driving forces for desalination of water. During the CDI process, ions are adsorbed onto the surface of electrodes by applying a low voltage electric field (DC<2V). In addition, the regeneration of the electrodes contains desorption of the electrosorbed ions from the surface of the electrodes to the water in the absence of the applied electric field. In the mechanism of CDI, separation and accumulation of ions in the electric field are the main processes and no additional chemicals are required in this technology. Therein, variety of electrode materials, electric field program, cell configurations and integrated structure with other techniques of water treatment were proposed to enhance the CDI performance. Materials with high electrical conductivity, high specific surface area, ion accessible porous structure, and good wettability are the proper electrode materials in order to increase the mass sorption capacity of the electrodes because it is the most important drawback of CDI technology. Therein, wide variety of materials including carbon-based nanostructures are used as electrode materials. Introducing a new method for preparation of modified nanostructured porous carbon-metal composite for increasing of water remediation rate and the capacity of ion sorption in CDI is the main novelty of this thesis. At the first step of this project, graphene oxide was synthesized via modified Hummer's method. Then, it was functionalized by hydrophilic functional groups such as phosphate group for preparation of modified electrodes. The functionalized graphene materials were characterized by a variety of methods; including: Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, powder x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analytical x-ray spectroscopy (EDAX), diffuse reflectance spectra (DRS), Brunauer¬−¬Emmett−-Teller, (BET) and Barrett−Joyner−Halenda (BJH) isotherms, four-point probe conductivity test (FPP), thermogravimetric analysis (TGA), and differential thermogravimetric analysis (DTG). Next, the graphene sponges were made in a freeze drier with the as-synthesized functionalized graphene samples. Then the materials were put in a furnace to make the reduced graphene containing samples. Metal foams have proper electrical and mechanical properties, thus those are valuable substrates for preparation of porous metal-carbon mixed composites. There in, the metal (Ni) foams were immersed in the same graphene containing slurries. Freeze-drying process were done on the functionalized graphene electrodes. After that, they were kept in tubular furnace for thermal treatments. In this way the binder free electrodes such as Ni/PPOGr-CNT/PoPy were made. So, the electrochemical characterization of the mixed carbon-metal composite electrodes were evaluated using CV, GCD and EIS methods. The modified electrode revealed high specific capacitance of 159 F/g in scan rate of 5 mV s-1 in 1 M NaCl. Also, the electrochemical stability of the electrode was evaluated by GCD analysis for 3250 cycles in the 1 M NaCl. Next, the binder free modified electrodes were applied for CDI studies. The modified electrodes revealed specific ion separation performance of 9 mg/g from 500 ppm of NaCl in aqueous media in a batch mode condition. Using the modified electrodes, a CDI prototype cell with water circulation was designed and its desalination performances were validated in operational water circulation condition. Finally, the parameters of electrosorption process such as concentration of salt, applied voltage, water flow rate, durability, and etc. were surveyed
  9. Keywords:
  10. Functionalized Graphene ; Graphene Oxide ; Water Treatment ; Desalination ; Capacitive Deionization ; Demineralizing ; Poly Phosphate-Graphene Composite ; Carbon Nanostructures

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