Controllable Preparation Of ZIFs-Derived Polymorphic Carbon Materials And The Study On Capacitive Deionization Properties

Capacitive deionization(CDI)technology is a new desalination technology.The desalination performance of capacitive deionizing technology depends largely on the properties of electrode materials themselves.The currently used electrode materials mainly include:activated carbon,carbon aerogel,carbon nanotubes,graphene,intercalation materials,metal organic framework materials(MOFs),etc.Derived from metal-organic framework as template or precursor after carbonization at high temperature,MOFs derived carbon materials have attracted much attention in CDI technology due to their diverse structures,well-developed pores,high specific surface area,adjustable pore size and functionalized pore surface.In this paper,two typical MOFs materials,ZIF-67 and ZIF-8,were used as precursors.A series of ZIF-67 based porous carbon materials with different morphologies were prepared by changing the atmosphere,and ZIF-8 based hierarchical framework porous carbon materials were prepared by template method.The differences in properties caused by different morphologies and pore structures,and the effects of these properties on the performance of CDI were studied in detail.The main research contents are as follows:1)Three different forms of ZIF-67 derived carbon materials were successfully prepared by using different atmospheres and preparation parameters.The morphology,element distribution,porous properties,surface properties,electrochemical properties and capacitive deionization properties of these ZIF-67 derived carbon materials were characterized and tested in detail.The results show that the in-situ generation of carbon nanotubes induced by ZIF-67 Co element in reducing atmosphere can increase the degree of graphitization of the material and enhance the conductivity of the material,which is conducive to electron conduction and improve the adsorption rate of the material.However,the generation of carbon nanotubes reduces the specific surface area of the material,resulting in a decrease in specific capacitance,wettability and zeta potential,which are not conducive to the electrical absorption of the material.Although the ZCNB(ZIF-derived carbon nanobox)calcined in nitrogen atmosphere does not contain carbon nanotubes,it has the highest specific surface area,wettability and surface charge,and the pore size distribution is closer to the hydration radius of salt ions,showing the best electric adsorption performance(6 mg·g-1).2)Using polystyrene microspheres as self-sacrificial templates,ZIF-8 materials with hierarchical porous structure(Hierarchical porous-ZIF-8,HP-ZIF-8)was successfully synthesized using a double-solvent-induced heterogeneous nucleation approach,followed by high-temperature calcination to obtain ordered macroporous carbon framework(OMCF),which we used as a CDI electrode material,and compare with microporous carbon framework(MCF)which is directly carbonized by ZIF-8.The results show that compared with MCF,OMCF with unique pore structure has a high specific surface area,which provides more adsorption sites for adsorption and increases the specific capacitance of the material.At the same time,the penetrating macroporous structure can provide channels for ion transport,accelerate the penetration of solution ions,and reduce the contact angle of the material,thereby significantly increasing the adsorption rate and adsorption capacity.These properties enable OMCF to exhibit excellent performance as a CDI electrode material,with a high adsorption capacity of 12.17 mg·g-1 in a 500 mg·L-1 NaCl solution at a voltage of 1.2 V,a flow rate of 20 mL·min-1.Compared with MCF,it has a higher specific surface area utilization rate.It proves that the material with macroporous structure has broad application prospects in the field of CDI,and provides a new way for the application of CDI in large-scale seawater desalination in the future.