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Development of Capacitive Deionisation Electrodes: Optimization of Fabrication Methods and Composition

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Development of Capacitive Deionisation Electrodes: Optimization of Fabrication Methods and Composition Title Page Development of capacitive deionisation electrodes: optimization of fabrication methods and composition By Shonny Nkuna A thesis submitted in fulfilment of the requirements for the degree of Magister Scientiae in the Department of Chemistry, South African Institute for Advanced Material Chemistry, University of Western Cape. Supervisor: Prof Bernard Bladergroen Co-Supervisor: Mr Bongibethu Hlabano-Moyo November 2017 i Declaration I declare that Development of capacitive deionisation electrodes: optimization of fabrication methods and composition is my own work, that it has not been submitted for any degree or examination in any other university, and that all sources I have used or quoted have been indicated and acknowledged by means of complete references. Shonny Nkuna November 2017 Signed…………………………………………………….. ii http://etd.uwc.ac.za Acknowledgements My sincere and utmost gratitude goes to the almighty God for his grace, the strength and wisdom that he has granted me. To my Supervisors Prof Bernard Bladergroen and Mr Bongibethu Hlabano-Moyo thank you very much for the opportunity you gave me and the excellent supervision, support and encouragement during the course of this work. To all the staff members and postgraduate students at South African Institute for Advanced Material Chemistry (SAIAMC) thank you for all the support, assistance and guidance. My greatest gratitude to the National Research Foundation (NRF) and Water Research Commission (WRC) for funding my studies. Thank you to Mr Earl McDonald for Electron Microscope Unit (EMU) University of the Western Cape for assistance with Scanning Electron Microscope (SEM). To Ms Hanlie Botha from Stellenbosch University chemical engineering department for all her assistance with BET analysis. To my mother Ms Johannah Mayimele thank you for all your love, support and the encouragement that kept me going. To the rest of my family and friends thank you so much for the support, love, encouragement and prayers throughout my studies. iii http://etd.uwc.ac.za Keywords Membrane Capacitive Deionisation Desalination Reverse Osmosis Nanofiltration Electrodialysis Multi-Effect Distillation Ion Exchange Activated Carbon Conductivity Electrode Binder Maximum Salt Adsorption Capacitance Scanning Electron Microscope Cyclic Voltammetry Brunauer-Emmett-Teller Porosity Surface Area Adsorption Desorption iv http://etd.uwc.ac.za Abbreviations AEM Anion Exchange Material ASAR Average Salt Adsorption Rate BET Brunauer Emmet Teller BM Batch Mode CB Carbon Black CC Constant Current CDI Capacitive Deionisation CEM Cation Exchange Material CNTs Carbon Nanotubes CV Cyclic Voltammetry N,N-DMAC N,N-Dimethylacetamide ED Electrodialysis EDLC Electric Double Layer Capacitor HDPE High Density Polyethylene IEM Ion Exchange Material IEX Ion Exchange MCDI Membrane Capacitive Deionisation MED Multi-Effect Distillation mSAC Maximum Salt Adsorption Capacity NF Nanofiltration PVDF Polyvinylidene Fluoride RO Reverse Osmosis SSA Specific Surface Area SAIAMC South African Institute of Advanced Material Chemistry SAC Salt Adsorption Capacity SEM Scanning Electron Microscope SP Single Pass TDS Total Dissolved Solids v http://etd.uwc.ac.za Abstract The objective of this research was to optimize the fabrication methods for and compositions of electrodes for the Membrane Capacitive Deionisation (MCDI) system. Two electrode fabrication methods were developed, namely a spray coating- and a casting method. The compositions of the electrodes were varied yielding a total of 14 different electrode in an attempt to optimize the fabrication methods and compositions of the electrodes. Three activated carbons were utilized in this study, TOB, YP50F and YP80F, these activated carbons have different surface areas and porosity therefore were affected different by the materials added in the ink. Carbon black and carbon nanotubes were used as conductivity additives to enhance the conductivity of the electrodes. Lastly a polymer binder was added to increase the mechanical integrity of the electrode, this polymer was typically PVDF. For some electrodes, PVDF was replaced with ion exchange polymers in an attempt to provide ion conductive properties to the electrodes. To establish the charge capacity of the electrodes Cyclic Voltammetry was used, BET analysis evaluated the surface area and porosity of the raw materials and fabricated electrodes. Scanning Electron Microscopy was used to verify surface morphology and uniformity. Ion adsorption capacity measurements were performed using a specially designed MCDI cell. The objectives of this study were achieved, the fabrication methods were optimized with the casting method producing superior electrodes. Apart from fulfilling the research objectives, the current research work generated significant scientific value by revealing how the production method impacts the electrode’s surface area and electrode adsorption capacity. vi http://etd.uwc.ac.za Table of Contents Title Page ................................................................................................................................................................ i Declaration ............................................................................................................................................................ ii Acknowledgements .............................................................................................................................................. iii Keywords .............................................................................................................................................................. iv Abbreviations ........................................................................................................................................................ v Abstract ................................................................................................................................................................ vi List of figures ........................................................................................................................................................ x Chapter 1 ............................................................................................................................................................... 1 1.1 Desalination Technologies ......................................................................................................................... 1 1.1.1 Reverse Osmosis .................................................................................................................................. 1 1.1.2 Nanofiltration ...................................................................................................................................... 2 1.1.3 Electrodialysis ..................................................................................................................................... 3 1.1.4 Multi-Effect Distillation ...................................................................................................................... 4 1.1.5 Ion Exchange ....................................................................................................................................... 5 1.1.6 Capacitive Deionization ...................................................................................................................... 7 1.2 Research Purpose Statement ..................................................................................................................... 8 1.3 Aims and Objectives ................................................................................................................................... 8 1.4 Conceptual Diagram .................................................................................................................................. 9 1.5 Thesis Outline ........................................................................................................................................... 10 Chapter 2 ............................................................................................................................................................. 11 2.1 Capacitive Deionization ........................................................................................................................... 11 2.1.1 Historical Perspective and Timeline of CDI ................................................................................... 12 2.1.2 Commercial Applications of CDI .................................................................................................... 14 2.1.3 Fundamentals of CDI: The Electric Double Layer Theory ........................................................... 15 2.2 Detailed Outline of CDI ........................................................................................................................... 16 2.2.1 CDI Flow Modes ............................................................................................................................... 16 2.2.3 Materials for Electrode Development and Design.......................................................................... 19 2.3 State of the Art CDI ................................................................................................................................. 21 2.3.1 Significance of CDI ........................................................................................................................... 21 2.3.2 Shortcomings of CDI .......................................................................................................................
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