Study Of Carbon Nanotubes And Its Composite As Electrodes For Capacitive Deionization

Due to the growing population on the earth and rapid development of modern industry, water crisis has been one of the challenges that the world is facing. Therefore, desalination of seawater and brackish water and treatment of wastewater has been one of the approaches to overcome the problem. However, the traditional water treatment technologies involving distillation, reverse osmosis, electrodialysis and ion-exchange have some intrinsic disadvantages, such as high maintenance cost, high energy consumption and secondary pollution. As a novel purification technology, capacitive deionization (CDI), also called as electrosorption, has aroused the attentions of many researchers because of its energy-saving, low cost and environment-friendliness. At present, more and more research institutes and companies are paying effort to promote its commercialization.As known, the desalination efficiency of a CDI unit is greatly dependent on the properties of electrode materials. Carbon nanotubes (CNTs) with high surface area, suitable pore structure and excellent electrical conductivity has been regarded as the promising candidate for CDI electrode material and widely used in water treatment. In this thesis, we focused on the fabrication methods of CNTs film electrodes for CDI. Two kinds of methods have been proposed and the comparison of electrosorptive performances between the electrodes prepared by the two methods has been made. Moreover, to enhance the electrosorptive capacity of CNTs film electrode, we manufactured CNTs-based composite film electrodes through the two methods. The main contents in this thesis are listed as below:1. CNTs film electrode and CNTs/RGO composite electrodes with various RGO content were fabricated via compression method and their electrosorption capacity were investigated. It was found that CDI performances of the CNTs/RGO composite electrodes were enhanced due to the "plane-to-wire"(Reduced graphene oxide (RGO) to CNTs) conducting network formed by RGO and CNTs which could improve the electron transfer and facilitate rapid transport of electrolyte ions within the electrodes. Among all electrodes, CNTs/RGO composite electrode with90:10weight ratio of CNTs to RGO exhibited best desalination performance.2. CNTs film electrode was prepared through electrophoretic deposition method. The electrophoretic conditions during deposition process were optimized and the electrosorptive behaviors of as-deposited CNTs film electrodes were investigated. The experimental results demonstrated that the CNTs film electrode in this work exhibited a comparable electrosorptive capacity in NaCl solution to other conventional carbon electrodes.3. Carbon nanotubes-polyacrylic acid (CNTs-PAA) composite film electrode was prepared by electrophoretic deposition method. The cation selectivity of CNTs-PAA composite film electrode was studied. It was found that the CDI unit cell based on CNTs-PAA composite film electrode showed higher desalination efficiency than that of the cell based on pure CNTs electrode due to the existence of PAA which served as the cation-exchange polymer.