Construction Of {P₂W₁₈} And {VW₁₂} Type Polyoxometalates And Its Photocatalytic,Electrocatalytic,and Sensing Propertie

Among the classical types of polyacids,the earliest developed and most widely used are Dawson and Keggin type compounds.The{P₂W₁₈}series in the Dawson family have stable structures and strong coordination activities,resulting in their rich structures and more excellent redox capabilities.The 1:12 Keggin structure has a small spatial resistance,making it easier to combine complex metal complexes to form various hybrid assemblies.{VW₁₂}is a relatively undeveloped Keggin system with few types and is difficult to synthesize,and its applications in various fields are also limited.Therefore,it is necessary to design and synthesize{P₂W₁₈}and{VW₁₂}hybrids,and to further study the properties in terms of photocatalytic,electrocatalysis and sensing.Therefore,this article relies on hydrothermal methods to select ligands that are more easily coordinated and suitable transition metals.Through parallel experiments,by adjusting the reactant ratio,environmental p H,and reaction temperature,three Dawson type phosphorus tungstate salts and four Keggin type vanadium tungstate salts were ultimately synthesized,and their photocatalytic,electrocatalytic,and sensing properties were carefully studied.Based on the structural testing of the compound and a series of structural characterization,the molecular formula of 1-7 was determined,and the results are as follows:[{Ag（bipy）}₈{Ag（Hbipy）（bipy）(HP₂W₁₈O₆₂)₂}]·3H₂O（1）[{Cu（bipy）}₂{H₂P₂W₁₈O₆₂}]·8H₂O（2）（pz）{Cu（pz）₂（H₂O）₄}[{Cu（bipy）}₂{P₂W₁₈O₆₂}]（3）[{Cu^I（bipy）}₄{VW^VW₁₁^VIO₄₀}]·3H₂O（4）[{Cu^I（bipy）₂}₂{Cu^I（bipy）}{VW₁₂O₄₀}]₂·H₂O（5）（tymp）[{Na（Typ）（H₂O）}{(V^IVO)₂V^VW₁₀^VIW₂^VO₄₀}]·H₂O（6）{Hbipy}₃[VW₁₂O₄₀]·6H₂O（7）（bipy=2,2’-Bipyridyl,bipy=4,4’-Bipyridyl,Typ=4-（2,4,5-tripyridin-4-ylphenyl）pyri dine,tymp=4-（2,4,5-tripyridin-4-ylphenyl）（1,4-methyl）pyridine）After analyzing the crystal structure,the crystal structures of the seven compounds were finally determined.Compounds 1-3 are all{P₂W₁₈}bridged{Ag（bipy）₂}n chains that form a 3D network with vacancies or 1D channels.The difference is that compounds 1 and 3 are dimers and monomer clusters modified by two complexes,respectively;Compound 2 is a complex modified double supported Dawson cluster.Compound 4 is a 3D network structure formed by a pair of{VW₁₂}clusters wrapped in a rich{Cu（bipy）}_n metal organic ligand chain;Compound 5 is a 3D supramolecular network formed by bridging a triple supported{VW₁₂}with Cu（bipy）₂;Compound 6 is a 3D structure with a large tunnel formed by{Na（Typ）（H₂O）}bridged double vanadium cap{VW₁₂};Compound 7 is a 3D supramolecular network structure modified by bipy.The cyclic voltammetric characteristics,electrocatalytic oxidation reduction,and sensing properties of seven compound glassy carbon electrodes（1-7-GCE）were studied.The test results show that 1-7-GCEs have very obvious reversible redox peaks,indicating that they have good multi-electron transfer capabilities.Both 1-7-GCE exhibited high catalytic activity for the oxidation of AA and reduction of H₂O₂,indicating that compounds 1-7 were excellent bifunctional electrocatalysts.The corresponding sensor tests show that 1-7-GCE exhibits wide linear range,low detection limit,high sensitivity,and selectivity in the detection of H₂O₂（AA）at different voltages,making it a promising dual functional sensing material.Comparing the electrocatalytic and sensing properties,compounds 1 and 2 were found to be superior to other compounds,indicating that metal organic chain modified 3D hole or pore structures exhibit greater advantages in electron transport.The photocatalytic study results of compounds 1-7 show that the seven compounds have high degradation efficiency,good cycle stability,and service life for common organic dyes MB,Rh B,MO,and AP.Studies on the photocatalytic mechanism show that the different degradation efficiency of compound 4 for different dyes is caused by different reaction paths.Compounds 1 and 2 have the highest photocatalytic degradation efficiency,which can be attributed to the rich metal organic ligand chains,increasing the active sites,and promoting ion/electron transport.On the other hand,a large number of holes and channels in the spatial structure increase the specific surface area of the material,allowing more redox active centers to participate in the photocatalytic reaction,thereby promoting the improvement of catalytic efficiency.