Preparation Of Ferroferric Oxide Composite For Hybrid Capacitive Deionization

The increasing of energy consumption and the worsening of ecological environment have fueled severe water scarcity worldwide.In terms of growing freshwater demands,brackish or sea water desalination is believed to be promising technologies to remove these obstacles.Currently,all these desalination methodologies applied in industrial production,including multi-effect distillation,multistage flash distillation and reverse osmosis suffer from various shortcomings,such as excessive energy consumption and expensive cost.Capacitive deionization(CDI)has attracted considerable enthusiasm due to its low cost and nontoxicity to environment.Carbon materials are the most widely used materials for CDI electrodes,including graphene,mesoporous carbon,and metal-organic framework-derived carbons.However,the low desalination capacity of carbon materials largely limits the application of CDI on an industrial scale.To address this issue,a hybrid capacitive deionization(HCDI)system comprised of carbon and pseudocapacitive electrodes has been developed.Among the currently reported HCDI electrode materials,transition metal oxides(TMOs)are one of the ideal electrode materials.Recently,because of its excellent electrochemical performance,Fe₃O₄electrode material has been applied in the field of desalination to obtain high desalination capacity.In this thesis,we mainly focus on the preparation of Fe₃O₄ and its composite electrode materials,the HCDI system was constructed by using it as the negative electrode and activated carbon as the positive electrode.The electrical conductivity and cycle stability of electrode materials can be improved by designing reasonable nanostructures,thus promoting the high desalination and cycling stability during CDI Process.The main contents of this thesis are as follows:1.Fe₃O₄ nanoparticles were prepared by heat treatment using ferric citrate as precursor.The results show that the Fe₃O₄ nanoparticles obtained at 450°C(FO-450)heat treatment have the highest specific surface area and the best electrochemical performance.The specific capacitance of FO-450 electrode can reach 162.4 F g^-1 at a scan rate of 2 m V s^-1.FO-450 was used as the negative electrode of HCDI system and activated carbon as the positive electrode.The desalting capacity of FO-450 electrode is 18.5 mg g^-1 in 500 mg L^-1 Na Cl solution,and the capacity retention rate could reach85.8%after 20 cycles.2.In order to further improve the desalination capacity,we synthesis of iron-containing complex precursor under solvothermal conditions with the following pyrolysis process under N₂ atmosphere to obtain two-dimensional(2D)-Fe₃O₄/C composites.Due to the dispersion of amorphous carbon,the aggregation of Fe₃O₄nanoparticles is effectively prevented,and the conductivity is enhanced,thus achieving excellent electrochemical performance.The 2D-Fe₃O₄/C-450 material with the best electrochemical performance obtained by 450°C heat treatment has a specific capacitance of 207.5 F g^-1 at a scan rate of 2 m V s^-1.The HCDI system(2D-Fe₃O₄/C-450//AC)was constructed with 2D-Fe₃O₄/C-450 as negative electrode and activated carbon as positive electrode showed excellent desalination performance(28.5 mg g^-1)and good cycle stability in 1.2 V voltage and 500 mg L^-1 Na Cl solution.3.To further improve the desalination capacity and long cycle stability,we have successfully synthesized Fe₃O₄@Ti₃C₂ materials via one-step hydrothermal method.The synergistic effect of Fe₃O₄ and Ti₃C₂ MXene can greatly improves the charge transfer,thus improving the electrochemical performance.Moreover,Fe₃O₄nanoparticles tightly coated on the surface of Ti₃C₂ MXene could further the protect the self oxidization,thus improving the cycle stability of HCDI process.Compared with Ti₃C₂ and Fe₃O₄,Fe₃O₄@Ti₃C₂ shown the highest specific capacitance(207.5 F g^-1)at a scan rate of 2 m V s^-1.In HCDI(Fe₃O₄//AC,Ti₃C₂//AC and Fe₃O₄@Ti₃C₂//AC)system,when the applied voltage is 1.2 V and the concentration of Na Cl solution is 500 mg L^-1,the desalination capacities of Fe₃O₄,Ti₃C₂ and Fe₃O₄@Ti₃C₂ electrode materials were20 mg g^-1,28 mg g^-1 and 44 mg g^-1,respectively.Fe₃O₄@Ti₃C₂ shown high desalination capacity and after 40 cycles test,he retention rate of desalination capacity is still up to82.0%,indicating that it also has good cycle stability.