Preparation And Capacitive Desalination Performance Of FeOCl Based Ion Deintercalation Electrode

Water is an indispensable resource for human survival and social development.With the continuous industrial and agricultural water consumption and more and more serious water pollution in recent years,the shortage of fresh water resources has become increasingly critical issue of human society.The traditional desalination technologies such as reverse osmosis,electrodialysis and distillation have been widely used.In recent years,compared to those conventional desalination technologies,a promising technology called Capacitive Deionization(CDI)has emerged as a robust,energy efficient,and cost effective technology for desalination of water with a low or moderate salt content.It has found their application in water desalination,waste water remediation and harvest valuable ions or remove harmful ion form a solution.Although many efforts have been made to explore the cation ion(Na+)storage electrode materials,anion(Cl-)ion storage electrodes are rarely investigated.This thesis focuses on the preparation of FeOCl based deintercalation electrode materials and their desalination performance.Firstly,FeOCl material was prepared by high temperature calcination method,and subsequent FeOCl/polypyrrole(PPy)composite electrode material was prepared by Vapor Deposition Polymerization(VDP)method.The as-prepared material and activated carbon(AC)are used as electrode materials,combined with ion exchange membranes with different configurations to construct a capacitive deionization device.The influence of voltage and electrolyte concentration on the desalination performance was studied,and the influence of the configuration of anion and cation exchange membranes on the desalination performance was also investigated.This study will offer a new idea and method to the solution of water scarcity and to develop more efficient and economic desalination system,and can contribute significantly to water treatment in the future.The main research contents are as follows:1?Iron oxychloride(FeOCl)was prepared by a one-step high-temperature calcination method.After X-ray diffraction(XRD)and scanning electron microscopy(SEM)analysis,the as-obtained FeOCl sample is pure phase crystal structure with fibrous morphology.Electrochemical tests show that the specific capacitance of FeOCl in 1M NaCl solution is 94.08Fg^-1 when the scanning speed is 1mVs^-1.Hybrid desalination(HCDI)devices with the FeOCl and Active Carbon(AC)assembled as the positive and negative electrode to adsorb Cl-and Na+,respectively.The desalination capacity is 53.27mgg^-1 when the working voltage is 1.2V and the initial conductivity is 2000 ?S cm^-1,which indicating that the FeOCl material can adsorb Cl-.The effect of ion exchange membrane with different configuration on the desalination performance of the HCDI was studied.The desalination capacity,the charge efficiency and energy consumption of the FeOCl(positive)//AC(negative)HCDI device without membrane is only 5.41mgg^-1,6.1%,and 2.49 kWh kg^-1,respectively.The M-HCDI(using Anion and Cation Exchange Membrane)device has a desalination capacity of 53.27mgg^-1,highest charge efficiency(88.9%)and the lowest energy loss(0.17 kWhkg^-1).The FeOCl//AEM-HCDI(Anion Exchange Membrane)device has a retention rate of 88%after 25 cycles of testing,indicating excellent cycle stability.By symmetrically assembled FeOCl(positive)//FeOCl(negative)capacitive desalination device and introducing different configurations of ion exchange membrane,The research results show that CDI(no membrane),CEM-CDI(cation exchange membrane),AEM-CDI and M-CDI exhibited 2.99mgg^-1,54.47mgg^-1,68.86mgg^-1 and 54.11mgg^-1 when the initial conductivity of feed solution is 2000?Scm^-1 and the working voltage is 1.2V,respectively.The result shows that whether an anion and cation exchange membrane is used at a single electrode or both electrodes,the desalination capacity and charge efficiency are greatly improved.2?The oxychloride/polypyrrole(FeOCl@PPy)composite material was prepared by VDP.SEM results show that PPy is uniformly polymerized on the surface of FeOCl.According to the BET test,the specific surface area of FeOCl@PPy is 17.67 m² g^-1,and the average pore diameter is 13.95nm.Electrochemical tests show that the composite with polypyrrole greatly increases the conductivity of FeOCl.The specific capacitance(213.37Fg^-1)of the composite is 2.27 times that of FeOCl when the scan rate is 1mVs^-1.A hybrid desalination device was constructed with FeOCl@PPy as the positive electrode and activated carbon(AC)as the negative electrode.At the same time,an asymmetric ion exchange membrane was introduced to test its desalination performance.The experimental results show that the introduction of a cation exchange membrane on the side of the carbon electrode can greatly alleviate the common ion effect on the negative electrode,effectively improve the overall performance of CDI to the level of M-HCDI(86.91mgg^-1),and the desalination capacity and the charge efficiencys can reach 86.44mgg^-1,94.7%,respectively.At the same time,the FeOCl@PPy composite material has a desalination retention rate of 88%after 15 adsorption-desorption tests.It shows that Faraday electrode materials can achieve higher charge efficiency without adding ion exchange membranes,and have good cycle stability.