Preparation Of Carbon-based Composite Electrode Materials For Capacitive Deionization

With the rapid population growth and the acceleration of urbanization,human demand for fresh water resources is increasing.At the same time,the rapid development of urbanization has also led to human beings facing the problem of fresh water resources shortage and the increasingly tense water pollution.Therefore,we need to effectively alleviate problems such as shortage of fresh water resources and water pollution.Capacitive deionization technology can not only desalinate seawater and brackish water,reuse of recycled water,but also remove heavy metals from waste water.It can achieve the purpose of increasing fresh water resources and purifying water,which is considered to be a water treatment technology with high efficiency,low cost,low energy consumption and pollution-free characteristics.Electrode materials play a key role in the capacitive deionization performance of this technology.At present,for the limited deionization capacity traditional carbon materials,containing activated carbon,porous carbon,carbon nanotubes,graphene and etc.,are restricted to large-scale practical applications.Aiming at the above-mentioned problems,this paper modified carbon-based composite materials through reasonable preparation route to obtain electrode materials with excellent capacitive deionization ability,and combined with relevant characterization to further explore the mechanism of removal of ions.The main research contents are as follows:(1)The zeolitic imidazolate skeleton-Zn Fe(ZIF-Zn Fe)precursor was synthesized through in-situ self-assembly,which was designing by zinc nitrate and ferrous sulfate as metal ligands,2-methylimidazole and polyvinylpyrrolidone(PVP)as an organic ligand and a dispersant with promoting the dispersion of Fe²⁺,respectively.And then after high-temperature calcination and pyrolysis treatment,a stable Fe₃C-N-C capacitive deionization electrode material was prepared.It was found that Fe ions doped into the carbon framework to form stable Fe-C bonds,which could change the electronegativity of carbon atoms near by Fe²⁺ions,locally regulate the distribution of electron density to form more active sites and enhance ion adsorption ability.N doping in the carbon framework could produce more defects and improve the hydrophilicity and electrical conductivity,which provided a guarantee for the rapid diffusion and transmission of ions in the solution through the polyhedral framework.The Fe₃C-N-C||N-C electrode displayed a deionization capacity of 30.08 mg g^-1 in a 500 mg L^-1 Na Cl solution at an applied voltage of 1.2 V with 40 m L min^-1 flow rate.In addition,the electrodes exhibited a good atability and regeneration performance.(2)By using zinc acetate and manganese acetate as metal ligands,trimesic acid as an organic ligand and PVP as a dispersing additive,the metal-organic skeleton-Zn Mn(MIL-Zn Mn)precursor was obtained.The nanoflower rod-like Zn Mn O/C(ZMOC)capacitive deionization electrode material was prepared after calcination at high temperature.By controlling the added amount of metal ligands and then regulating the structure of ZMOC,the ZMOC space structure could accommodate more ions.It was beneficial to provide more space location for ions adsorption.With the bimetal coordinating role played during the capacitive deionization process,it promoted to improve the hydrophilicity and electrical conductivity of the material,and shorten the electron transmission path and ion diffusion distance.In the capacitive deionization study,ZMOC-2||AC electrode performed the deionization capacity of 31.64 mg g^-1 in a 500 mg L^-1 Na Cl solution at40 m L min^-1 flow rate under 1.2 V applied voltage,indicating that excellent capacitive deionization ability.This was due to the fact that ZMOC-2 could not only adsorb ions on the surface of the material with the form of an electric double layer,but also reversibly embed the ions into the lattice gap of the material in the way of intercalation to achieve the purpose of removing/recovering ions.The electrodes displayed excellent capacity deionization ability and recycling ability.What's more,the process had great capacitive removal efficiency for Pb heavy metal ion in waste water.(3)By designing graphene oxide as a dispersing and conductive additive,using dopamine hydrochloride to coat the Si O₂ pellet template,the porous carbon(PC)precursor was acquired after high-temperature calcination and alkali etching treatment.The titanium dioxide/porous carbon(CTO-PC)capacitive deionization electrode material was prepared by the atomic deposition(ALD)strategy,which could control the Ti O₂ amount deposited uniformly and accurately on the PC surface.It has been demonstrated that the nanolayer of Ti O₂ was formed by reaction on the surface of porous carbon by using an ALD strategy,which could effectively build the Ti-C redox interfaces betwwen Ti O₂ and PC.The interfaces could efficiently enhance the electronic transmission of pseudo-capacitance reaction and greatly improve the kinetics of pseudo-capacitance reaction.And thus,the nanolayer of Ti O₂on porous carbon was beneficial to facilitate ions diffusion/transmission and adsorption/insertion.It was noted that the deionization capacity was as high as 38.54mg g^-1 in a 500 mg L^-1 Na Cl solution at 1.2 V with 40 m L min^-1.During this deionization process,the energy consumption for 20CTO-PC||PC was 84 J g^-1 with energy efficiency of 11.8%.Furthermore,the charge efficiency and water recovery of the electrode were 89%and 35%,respecitively.Additionally,this process had excellent removal efficiency to treat complicated water containing multiple metal ions.It processes broad development and application prospects in the environment.