Preparation And Properties Of Nickel Vanadate-based Metal-organic Framework Materials And Their Derivatives

Metal-organic framework compounds(MOFs)have attracted much attention in the field of electrode modification and catalysis because of their high specific surface area,adjustable pore size and abundant redox and catalytic active sites.Polyoxometalates(POMs)have excellent physical and chemical properties,such as reversible ability to accept electrons and protons,adjustable size and high chemical stability.Polyoxometalate-based metal-organic framework compounds(POMOFs)have the structural advantages of both POMs and MOFs,and those are a kind of functional materials with great application prospects.This thesis aims at the application of micro-nano structured nickel vanadate-based metal-organic framework compounds and their derivatives in the application of electrochemistry and catalysis.The as-prepared materials were characterized and their properties on electrode modified materials(supercapacitors and electrocatalytic decomposition of water)and catalytic reduction of organic(inorganic)pollutants were then studied.The main research contents and conclusions are as follows:(1)Nickel vanadate-based metal-organic framework materials POMOF(V,Ni)Three kinds of POMOFs materials have been prepared through hydrothermal method using ammonium metavanadate(NH4VO3),nickel acetate tetrahydrate(Ni(CH3COO)2·4H2O)and different ligands(such as 1,10-phenanthroline,1,1'-(1,4-butanediyl)bis(imidazole)and2,2'-bipyridine)as main raw materials,in which those are named as POMOF(V,Ni_phen)(I),POMOF(V,Ni_bbi)(II),and POMOF(V,Ni_bipy)(III),respectively.The experimental results show that POMOF(V,Ni)nanomaterials can be prepared by mixed-solvents(anhydrous ethanol and water).The morphology,particle size,specific surface area and pore size distribution of POMOF(V,Ni)materials are varies obviously with the different ratios of anhydrous ethanol and water,which indicates that the solvent effect is significant in the preparation of the compounds POMOF(V,Ni).The structures of the above three compounds were then characterized by various methods and their properties in electrode modification materials and catalytic reduction were also studied.The results show that the POMOF(V,Ni_bbi)₄0 has excellent performance as electrode modification material for supercapacitor,and its specific capacitance can reach493.3 F/g at 1 A/g current density.And the compound(II)presents the best electrocatalytic hydrolysis performance,the voltage required to drive 10 m A/cm2 current density is only 139.9mV in HER test(POMOF(V,Ni_bbi)₆0),and the voltage required to drive the current density of 10 m A/cm2 is 353.0 m V in OER test(POMOF(V,Ni_bbi)₃0).The POMOF(V,Ni_bipy)₂0has the largest specific surface area,up to 761.98 m2/g.The material has excellent catalytic reduction activity,in which the catalytic reduction rate is 1.19 min-1 in 3 min for complete catalytic reduction of 4-nitrophenol,and the reaction rate of catalytic reduction of Cr(VI)to Cr(III)is 0.277 min-1 in 6 min.(2)Thermal decomposition derivatives of the POMOF(V,Ni)Two kinds of nanocomposites,V2O3@Ni(IV)and VO2@Ni O(V),have been prepared at different temperature in N2 protected atmosphere by calcining compound(I)and compound(II)as precursors,respectively.The experimental results show that the calcination temperature has a significant effect on the micromorphology and phase structure of the as-prepared composites,and further affects those electrochemical and catalytic properties.The structural characterization and properties of the above two materials were also studied.The experimetnal results of the composite(IV)of V2O3@Ni₆00 show that its specific capacitance can reach 237.2 F/g at current density 1A/g when it is used as electrode modification material of supercapacitor,and a current density of 10 m A/cm2 at a voltage of only 75.3 m V can be obtained when it used as an efficient electrocatalyst for hydrogen evolution.The V2O3@Ni₆00 presents an excellent reduced catalyst,in which it can almostly reduce Cr(VI)to Cr(III)with the reaction rate of 0.129 min-1within 16 min.The performances of the composite material(V)of VO2@Ni O₃50 indicate that its specific capacitance can reach 377.7 F/g at current density of 1 A/g when it served as a supercapacitor electrode modification material,and the current density of 10 m A/cm2 with a voltage of 35.6 m V can be obtained when it used as an efficient electrocatalyst for hydrogen evolution.The compound(V)of VO2@Ni O₃50 presents excellent catalytic reduction activity,in which it can completely catalyze the reduction of Cr(VI)to Cr(III)in 5 min with the reaction rate of 0.398min-1.The exploration and study of this thesis provides a reliable theoretical and experimental basis for the preparation of POMs-based nano-porous metal-organic framework compounds in electrochemistry and catalysis.