The Preparation And Research On Dichlorination Performance Of Carbon-based Electroactive Materials Based On Confined Sub-nanometer Pores

Water shortage and pollution have become a major challenge in China due to the rapid growth of the global population and climate change,especially the discharge of industrial wastewater.As a common anion in waste water,chloride ion is widely found in waste water discharged from landfill,paper making,canned seafood and tanning industries.However,high concentrations of chloride ions often pollute drinking water,cause soil salinization,harm crop growth and corrode industrial equipment.The main traditional techniques for chloride removal are chemical precipitation,ion exchange and membrane separation,but these methods still suffer from the disadvantages of being prone to secondary contamination and low separation efficiency.Thus,it is increasingly urgent to develop an efficient and clean chlorine ion removal technology.Electrically controlled ion exchange（ESIX）technology,as a new ion separation method,has attracted extensive attention of researchers in recent years because of its high selectivity and no secondary pollution.In the ESIX process,the external electric field is the main driving force for ion separation,which can reversibly place and release ions from solution during the transition between oxidation and reduction states.As the core of ESIX systems,the development of new EIXMs is still our current focus.In this paper,a kind of EIXMs with sub-nano channels is synthesized,which is realized by the pore size effect of nanomaterials.On this basis,EIXMs with selective separation function for chloride ions were synthesized by chemical oxidation method combined with ion imprinting technology.In recent years,metal-organic frameworks（MOFs）have been regarded as one of the materials for constructing high performance ion separation due to their adjustable pore size,high specific surface area and good structure at nanometer scale.However,most MOFs have poor electrical conductivity and water stability,making them difficult to apply directly to ESIX.The carbonization of MOFs makes up for this shortcoming to some extent.In this work,zeolitic imidazolate framework（ZIF-8）derived nano-porous carbon（NC-X-A）with confined sub-nanometer pores was synthesized by acid leaching and alkali activation after the carbonization of ZIF-8 precursor for the selective electrochemical separation of chloride ions（Cl^-）.Here,the uptake capacity and selectivity of Cl^-were improved by changing the carbonization temperature to tune the specific surface area and pore size.Based on the size confinement effect and the difference in free energies of dehydration,the obtained optimum carbon film,i.e.,NC-1000-A coated electrode,exhibited separation factors of 1.384,1.952and 2.970 for Cl^-/Br^-,Cl^-/F^-and Cl^-/SO₄^2-,respectively.It also showed fast uptake/release ability with an uptake equilibrium time less than 90 min.The Cl^-uptake capacity reached to64.06 mg·g^-1 and retained 99.7%of its initial value even after 1000 uptake/release cycles due to its porous structure with high specific surface area,good electrical conductivity and extra electric driving force during the ESIX process.Thus,it is expected that this kind of carbon film would be applied as a promising electroactive material for the selective separation of Cl^-from wastewater.ZIF-8 derived carbon material has the characteristics of large specific surface area and large micropore volume,which is a promising electroactive material used in ESIX.However,some serious problems such as low conductivity and large aperture size still exist,which limit its ESIX performance.To solve the above problems,the conductive polymer polypyrrole（PPy）with imprinted chloride ions was in-situ polymerized in the nanocrystal channel of NC-1000-A to obtain NC-1000-A@PPy composite materials.ESIX performance of NC-1000-A@PPy composites were tested and analyzed.The highly selective separation of chloride ions was realized by the synergy of ion imprinting effect of PPyand size screening effect of NC-1000-A.The adsorption capacity of the newly prepared NC-1000-A@PPy is as high as 74.16 mg·g^-1,and the selectivity of the membrane electrode is significantly improved.The Separation coefficient of Cl^-/SO4^2-is 5.31.Therefore,NC-1000-A@PPy is expected to be a highly efficient ESIX electrode material.