Development of conventional water treatment and desalination technologies are becoming in full swing. Additionally, searching on alternatives desalination methodologies attracted great attentions to avoid the disadvantages of the traditional desalination methods. Capacitive deionization (CDI) is a s...
Development of conventional water treatment and desalination technologies are becoming in full swing. Additionally, searching on alternatives desalination methodologies attracted great attentions to avoid the disadvantages of the traditional desalination methods. Capacitive deionization (CDI) is a second generation of electrosorption technique for removing the salt ions from the brackish water. CDI is a promising perspective for water purification technologies as a robust, energy efficient, friendly environmental and economic technology for desalinating of brackish water. The electrode materials play an important role in electrosorption performance. According vast literature review, it was found that carbon is the best candidate to be exploited as electrode in the CDI units due to the good electrical conductivity, high corrosion resistance, and non-toxicity characteristic. However, up to date, the invoked carbon nanostructures in the CDI technology suffer from low specific surface area (e.g. carbon nanofibers) or low wettability or low specific capacitance (e.g. graphene). This thesis highlights the current research status of development carbon nanostructured based CDI electrode materials. This present thesis details the study of desalination performance of capacitive deionization using engineered pours carbon nanostructured or through carbon doped metal oxide to achieve the requirement of CDI electrode. Creating pores and increase the specific surface area, enhance surface wettability, different morphologies and optimized metal oxide loading content are studied as promising electrode materials for capacitive deionization. Their synthesis, physical characterization and electrochemical properties are discussed in detail. In the present study, two effective approaches of modified carbon nanofibers (NFs) and their performances as CDI electrode are introduced. Multi-channel carbon nanofibers were synthesized by using low cost, high yield and facile method; single-nozzle electrospinning technique. Stabilization and graphitization of electrospun nanofiber mats composed of polyacrylonitrile (PAN) and poly(methyl methacrylate) (PMMA) leads to form multi channels CNFs due to the difference in the physicochemical characteristics of the two polymers and complete thermal decomposition of the PMMA during the graphitization step. Typically, according to PMMA content, three formulations were prepared 0, 25 and 50 wt% PMMA with respect to PAN. Furthermore, to properly evaluate the introduced modified CNFs, graphene was prepared using the chemical rout. In the second approach, hollow carbon nanofibers (HCNFs) as highly efficient electrodes for capacitive deionization were prepared using co-axial electrospinning. Briefly, synthesis of electrospun poly(methyl methacrylate) (core) and poly(acrylonitrile) (shell) polymer solutions via co-axial nozzle followed by oxidative stabilization then carbonization. The morphology, pore structure and electrochemical performance were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), Nitrogen adsorption/desorption isotherms, and cyclic voltammetry, respectively. All the introduced solid CNFs have been synthesized using facile, simple, high yield, low cost, and effective technique; electrospinning. Furthermore, incorporating of metal oxides such as (MnO2, TiO2 and SnO2) in carbon electrodes to improve the electrochemical performance and wettability behaviour of the electrode materials was performed in the present thesis. Novel strategy for rapid transformation of graphite into graphene intercalated with nanostructured MnO2 with morphology control was introduced by one pot reaction, low-time consuming, eco-environmentally method. Herein, a rapid conversion of graphite into graphene structure was suggested through vigorous oxidation using ammonium peroxysulphate and hydrogen peroxide in presence of manganese sulfate followed by reduction step using piperidine under a microwave irradiation. It was demonstrated that formation of MnO2 nanostructures during the exfoliation process has a great impact to separate the graphene sheets as the metallic nanostructures wedged among the sheets. Interestingly, morphology control could be performed; MnO2-nanorods and MnO2-nanparticles@graphene could be prepared. Graphene/tin dioxide nanoparticles composites (Gr/SnO2) with different proportions were successfully synthesized via microwave irradiation; their electrosorption performances in CDI unit were investigated. The morphology, crystal structure and electrochemical performance were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and cyclic voltammetry. The obtained results indicated that incorporation of SnO2 into graphene has a great impact for enhancing the electrosorption capacity. Intercalating of TiO2 nanorods between graphene nanosheets were successfully synthesized by hydrothermal technique to exploit the superior advantages of graphene and simultaneously improve the overall electrochemical characteristics. The phase morphology, crystal structure and elemental analysis were confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Electrochemical properties were evaluated by a cyclic voltammetry (CV) test. Moreover, the desalination efficiency was investigated in a prototype MCDI unit. Furthermore, the influence of TiO2 loading was studied. Commercially, activated carbon is the most widely used carbon materials in CDI electrodes. To overcome its known low wetability, titanium dioxide nanofibers (TNFs) were anchored on activated carbon as hybrid networks electrode for capacitive deionization. The incorporation of TiO2 nanoparticles into activated carbon showed effective approach to enhance the desalination performance. Compared to nanoparticulate morphology, nanofibers have large axial ratio which provides better electrosorption performance. Herein, for the first time, electrospun TiO2 nanofibers (TNFs) were exploited with activated carbon to form hybrid networks electrode for CDI technology. The phase morphology and crystal structure were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Electrochemical behaviour was evaluated by a cyclic voltammetry (CV). Furthermore, the desalination performances under different voltages and concentrations during CDI cell were investigated as well as the TiO2 nanofibers content was optimized. Keywords: Water desalination; Capacitive deionization; Membrane capacitive deionization; Carbon nanofibers; Electrospinning; Graphene/metal oxide nanocomposite.
Development of conventional water treatment and desalination technologies are becoming in full swing. Additionally, searching on alternatives desalination methodologies attracted great attentions to avoid the disadvantages of the traditional desalination methods. Capacitive deionization (CDI) is a second generation of electrosorption technique for removing the salt ions from the brackish water. CDI is a promising perspective for water purification technologies as a robust, energy efficient, friendly environmental and economic technology for desalinating of brackish water. The electrode materials play an important role in electrosorption performance. According vast literature review, it was found that carbon is the best candidate to be exploited as electrode in the CDI units due to the good electrical conductivity, high corrosion resistance, and non-toxicity characteristic. However, up to date, the invoked carbon nanostructures in the CDI technology suffer from low specific surface area (e.g. carbon nanofibers) or low wettability or low specific capacitance (e.g. graphene). This thesis highlights the current research status of development carbon nanostructured based CDI electrode materials. This present thesis details the study of desalination performance of capacitive deionization using engineered pours carbon nanostructured or through carbon doped metal oxide to achieve the requirement of CDI electrode. Creating pores and increase the specific surface area, enhance surface wettability, different morphologies and optimized metal oxide loading content are studied as promising electrode materials for capacitive deionization. Their synthesis, physical characterization and electrochemical properties are discussed in detail. In the present study, two effective approaches of modified carbon nanofibers (NFs) and their performances as CDI electrode are introduced. Multi-channel carbon nanofibers were synthesized by using low cost, high yield and facile method; single-nozzle electrospinning technique. Stabilization and graphitization of electrospun nanofiber mats composed of polyacrylonitrile (PAN) and poly(methyl methacrylate) (PMMA) leads to form multi channels CNFs due to the difference in the physicochemical characteristics of the two polymers and complete thermal decomposition of the PMMA during the graphitization step. Typically, according to PMMA content, three formulations were prepared 0, 25 and 50 wt% PMMA with respect to PAN. Furthermore, to properly evaluate the introduced modified CNFs, graphene was prepared using the chemical rout. In the second approach, hollow carbon nanofibers (HCNFs) as highly efficient electrodes for capacitive deionization were prepared using co-axial electrospinning. Briefly, synthesis of electrospun poly(methyl methacrylate) (core) and poly(acrylonitrile) (shell) polymer solutions via co-axial nozzle followed by oxidative stabilization then carbonization. The morphology, pore structure and electrochemical performance were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), Nitrogen adsorption/desorption isotherms, and cyclic voltammetry, respectively. All the introduced solid CNFs have been synthesized using facile, simple, high yield, low cost, and effective technique; electrospinning. Furthermore, incorporating of metal oxides such as (MnO2, TiO2 and SnO2) in carbon electrodes to improve the electrochemical performance and wettability behaviour of the electrode materials was performed in the present thesis. Novel strategy for rapid transformation of graphite into graphene intercalated with nanostructured MnO2 with morphology control was introduced by one pot reaction, low-time consuming, eco-environmentally method. Herein, a rapid conversion of graphite into graphene structure was suggested through vigorous oxidation using ammonium peroxysulphate and hydrogen peroxide in presence of manganese sulfate followed by reduction step using piperidine under a microwave irradiation. It was demonstrated that formation of MnO2 nanostructures during the exfoliation process has a great impact to separate the graphene sheets as the metallic nanostructures wedged among the sheets. Interestingly, morphology control could be performed; MnO2-nanorods and MnO2-nanparticles@graphene could be prepared. Graphene/tin dioxide nanoparticles composites (Gr/SnO2) with different proportions were successfully synthesized via microwave irradiation; their electrosorption performances in CDI unit were investigated. The morphology, crystal structure and electrochemical performance were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and cyclic voltammetry. The obtained results indicated that incorporation of SnO2 into graphene has a great impact for enhancing the electrosorption capacity. Intercalating of TiO2 nanorods between graphene nanosheets were successfully synthesized by hydrothermal technique to exploit the superior advantages of graphene and simultaneously improve the overall electrochemical characteristics. The phase morphology, crystal structure and elemental analysis were confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Electrochemical properties were evaluated by a cyclic voltammetry (CV) test. Moreover, the desalination efficiency was investigated in a prototype MCDI unit. Furthermore, the influence of TiO2 loading was studied. Commercially, activated carbon is the most widely used carbon materials in CDI electrodes. To overcome its known low wetability, titanium dioxide nanofibers (TNFs) were anchored on activated carbon as hybrid networks electrode for capacitive deionization. The incorporation of TiO2 nanoparticles into activated carbon showed effective approach to enhance the desalination performance. Compared to nanoparticulate morphology, nanofibers have large axial ratio which provides better electrosorption performance. Herein, for the first time, electrospun TiO2 nanofibers (TNFs) were exploited with activated carbon to form hybrid networks electrode for CDI technology. The phase morphology and crystal structure were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Electrochemical behaviour was evaluated by a cyclic voltammetry (CV). Furthermore, the desalination performances under different voltages and concentrations during CDI cell were investigated as well as the TiO2 nanofibers content was optimized. Keywords: Water desalination; Capacitive deionization; Membrane capacitive deionization; Carbon nanofibers; Electrospinning; Graphene/metal oxide nanocomposite.
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