Study of Graphene and Its Composite as Electrodes for Capacitive Deionization
|School||East China Normal University|
|Keywords||graphene electrosorption capacitive deionization (CDI) doublelayer capacity|
Capacitive deionization (CDI), also called electrosorption, are attracting more and more attentions with the development of carbon materials due to its promising properties, such as high desalination efficiency, low energy consuming and environmental-friendliness. In the21st century, with the increase of world’s population and the development of modern industry, energy and environment crisis, especially the portable water crisis have influenced the economy and people’s life. However, the traditional desalination technologies, such as reverse osmosis, electro-dialysis and ion-exchange, have their own disadvantages, such as high energy and capital intensity. Currently, the CDI is thought to be a good alternative which can achieve the desalination with low cost and high efficiency. Thus, from a point view of basic theory and practical applications, it is necessary to develop and spread this new desalination technology.In this thesis, the graphene, GNFs and their composite were prepared by a facile chemical approach and they were then proposed as electrode for capacitive removal of NaCl. The electrosorption performance of as-prepared electrodes was investigated. Besides, we proposed and developed a novel membrane capacitive deionization (MCDI) technology. The main contents in this thesis are summarized as below:1. The graphene and GNFs were prepared by chemical method. The morphology, micro-structure, electrochemical property and CDI performance of graphene and GNFs were investigated, respectively. It is found that the electrosorption of ions onto graphene and GNFs electrode follows the Freundlich and Langmuir isotherm, respectively, and they both obey the pseudo-first-equation. In addition, a comparative study was carried out to explore the electrosorption behavior of SWCNTs, DWCNTs, AC and GNFs from a point view of adsorption kinetics. Finally, a possible mechanism was proposed to clarify the difference between the GNFs and AC electrode on electrosorption performance.2. The graphene and activated carbon (GAC) nanocomposite was prepared by chemical method and it was then proposed as CDI electrode. It is found that the GAC with20wt%graphene (GAC-20) has the best capacitive behavior and electrochemical peoperty. Furthermore, the desalination experimental result implies that the electrosorpive capacity of GAC-20is higher than that of either pure graphene or pure AC electrode. Meanwhile, it is found that the graphene serves as a flexible bridge to form a "plane-to-point"(graphene to AC) conducting network, which is beneficial to decrease the aggregation of AC particles, resulting in an improved electrosorption performance. In addition, the GAC electrode could be regenerated very well.3. A MCDI was proposed. Regardless of the solution concentration, the removal efficiency of MCDI. is proportional to its cell voltage and higher than corresponding CDI device. The kinetics analysis presents that the ion-exchange membrane is beneficial to enhance the ions transfer speed in solutions. Meanwhile, the electrosorption behavior of MCDI follows the Langmuir isotherm, indicating the monolayer adsorption and no change in adsorption behavior when ion-exchange membranes are introduced into CDI system. Besides, the charge efficiency of MCDI is higher than that of CDI due to the minimized co-ions impaction. In addition, the MCDI device has a good regeneration property which is critical to its commercialization.