The Study On The Synthesis And Capacitive Deionization Behavior Of Metal Organic Frameworks-derived Hierarchical Porous Carbon

Capacitive deionization（CDI）owning great potential in desalination,illustrates advantages including low energy consumption,low cost,no secondary pollution and wide application ranges.High efficient desalination electrode materials as the core element in the development of CDI have been studied widely.In this work,the fabrication method of metal organic framework（MOF）derived porous carbon as well as the structure-activity relationship between the properties of electrode materials and their desalination performance was investigated.Briefly,the research covers following four parts:1 Mesoporous carbon nanospheres（MCs）was prepared by pyrolysis ZIF-8 powder with Ar+4%H2 at 1000 ℃ directly.The formation of metal oxides was inhibited successfully due to the introduction of reductive gas,and therefore chemical pollution caused by acid pickling was avoided efficiently.Electrochemical result shows that MCs electrode has high specific capacitance of 215.72 F/g at 5 mV/s.Moreover,CDI result exhibits that MCs electrodes achieved desalination capacity of 12.03 mg/g with good regeneration.2 Nirogen-doped grahpitic carbon polyhedrons（NGCPs）with high degree sp-2 hybridization was synthesized by pyrolysis ZIF-8 under low pressure and nitrogen atmosphere directly.Low pressure was employed to accelerate the.overflow rate of Zn steam and avoid the structural damage.Therefore,a typical dodecahedron structure was maintained and a hollow porous structure was achieved.Further,NGCPs exhibit a high specific surface area of 1134 m²/g,N content of 3.73%and a high degree of graphitization crystallinity.Additionally,profit from its structural characteristics,the NGCPs electrode shows a high specific capacitance of 307.4 F/g at scan rate of 10 mV/s.The maximum salt removal capacity of NGCPs is obtained as 17.73 mg/g with an ultra-high salt adsorption rate of 4.14 mg/（g·min）and good regeneration performance.3 The mixed powder of ZIF-8/Ti（SO₄）₂ was pyrolysis in low pressure and nitrogen atmosphere,in which condition,O and S decomposed from titanium salts modify the derived carbon structure by doping and etching.Significantly,the obtained open hollow porous carbon（OHPCs）exhibits a specific surface area of 1025.9 m²/g and abundant pore structure which contains micropore,mesopore and macroporoe.Further,it has been confirmed that the enhancement in conductivity and hydrophilicity were profited from the doping of N,O and S elements.Remarkably,OHPCs electrode illustrate ultra-high specific capacitance of 344 F/g at scan rate of 10 mV/s and maximum desalination capacity of 16.4 mg/g with enhanced salt adsorption rate of 5.17 mg/（g·min）.4 Hybrid carbon nanoclusters（HCNs）of carbon polyhedron and carbon nanotubes（CNTs）was synthesized in a chemical vapor deposition（CVD）furnace through self-catalytic-assembling of ZIF-67.The cross-linking of cobalt catalyzed CNTs and carbon polyhedrons promotes the long-range conductivity and regulates the pore structure of the electrode.It has been proved that HCN at 650 ℃（HCN-650）illustrate the largest specific surface area（171.6 m²/g）,the best mesoporous network structure as well as mesopore characteristics among all HCNs samples.A fast electron transport path provided by CNTs was confirmed by electrochemical measurements.In terms of capacitive deionization test,salt removal capacity of HCN-650 electrode is 7.08 mg/g and the adsorption behaviour could be simulated by modified Doona modeling.In summary,reductive atmosphere（Ar+4%H2）as well as the cooperation of N2 and low pressure atmosphere can avoid metal residues in derived carbon and maintain the structure effectively.As an activator,Ti（SO₄）₂ has the effects of pore/morphology regulation and atomic doping.Additionally,the self-assembled of CNTs modified the conductivity and pore structure of the desalination electrode remarkably.Therefore,desalination electrodes obtained in this paper have been enhanced in corresponding properties.