Synthesis And Photoelectric Properties Of Flexible Ligand-imduced Basket-based Phosphomolybdate

As an important branch of non-classical polyacids,basket molybdate phosphomolybdate is a hybrid heteropoly blue composed of MO? and MO?.It shows good mixed valence delocalization phenomenon and its band gap is between 2.7-3.2.It has good semiconductor properties and is an ideal photocatalytic material.In addition,the unique cage structure and more molybdenum atoms of the basket compound make it have stronger reversible multi-electron redox ability,which is a potential pseudocapacitive material.However,the synthesis of basket compounds is difficult due to the instability of the intermediates that form basket compounds and the large steric hindrance of basket itself,which limits the research on the properties of these compounds.In this paper,eight basket-type compounds were synthesized by one-step hydrothermal method,by changing the pH value of the mixed solution and the type of transition metal,by taking full advantage of the activation of the inert oxygen atoms in the basket position by the flexible ligand and combining the coordination advantages of the rigid ligand.The structure and molecular formula of compound 1-8 were determined by means of elemental analysis,infrared absorption spectroscopy,thermal stability and single crystal X-ray diffraction.(Hbimi)4(H2bimi)2{Sr(?)P6Mo18O73}·4.5H2O(1)(EDA)8[{Mn(H2O)2}2{Sr(?)P6Mo18O73}2]2·34H2O(2)(H2bimb)6[{Cd(H2O)4.5}2{Sr(?)P6Mo?2Mo?16O73}2]·5H2O(3)(H2bimb)(H2bpy)4[{Ni(H2O)2} {Sr(?)P6Mo18O73}2]·4H2O(4)[{Na(H2O)2.5}2{Ni(bipy)(H2O)}4{Sr(?)P6Mo?4Mo?14O73}]·4H2O(5)(H2bib)3[{Cu(H2O)4} {Sr(?)P6Mo?2Mo?16O73}]·2H2O(6)(H2bpp)4[{Na(H2O)2}2{Co(H2O)2}{Sr(?)P6Mo18O73}2]·3H2O(7)(bih)2[{Na(H2O)2}3{Mn(H2O)2}4{Sr(?)P6Mo18O73}2](8)(bimi=Benzimidazole,EDA=Ethylenediamine,bimb=1,4-Bis(imidazol-1-ylmethyl)benzene,bpp=1,3-Di(4-pyridyl)propane,bpy=4,4-bipy,bipy=2,2-bipy,bib=1,4-Bis(Imidaz ol-1-yl)butane,bih=1,6-bis(imidazol-1-yl)hexane)The crystal structure analysis showed that compound 1 was a 3-D supramolecular split-layer network structure formed by benzimidazole ligand as the linkage unit.The basic structural units of compound 2-4 are dimer clusters connected by {Mn(H2O)2},{Cd(H2O)4.5} and {Ni(H2O)2},respectively.The difference is that compound 2 is a three-dimensional supramolecular network with channels formed by one-dimensional chains and two-dimensional surfaces extended in the ABAB way,while compound 3 and 4 are connected in order with regular 1-D channels.Compound 5 is a one-dimensional chain-like basket structure modified by {Ni(Bipy)(H2O)} complex and{Na(H2O)2.5} complex.Compound 6 is a basket-shaped one-dimensional chain structure modified by {Cu(H2O)4} complex.Compound 7 is a one-dimensional chain-like basket structure modified by {Na(H2O)2} complex and {Co(H2O)2} complex.Compound 8 is a novel two-dimensional layered structure formed by {Na(H2O)2} linkage structure and{Mn(H2O)2} linkage structure.The glassy carbon electrode was prepared by using compounds 1-8 as active substances.Cyclic voltammetry,galvanostatic charge-discharge,impedance,cyclic stability and electrocatalysis were tested respectively.Test results show that the high dimension of compounds than capacitance and cycle stability are higher than zero dimensional compound,transition metal in the dimer of key higher than simple zero dimensional compound,the main reason is that the introduction of transition metals can not only provide more redox center,can also be induced to form the structure of the different channel,with the basket itself cage structure,increase the electronic transmission under the condition of dual space,promotes the transfer of electrons and ions.The results of electrocatalytic test showed that compounds 1-8 could both catalyze the oxidation of AA and the reduction of H2O2,which were potential bifunctional catalytic materials.Of compound photocatalytic test results show that the eight compounds have MB,RhB,MO in sewage and other common organic dyes,has good degradation effect,compared to many other structure of the compounds in the acid degradation efficiency,basket type compound is more outstanding,the performance of the catalytic effect is better,the degradation efficiency is lower,this is because the basket cage structure of itself,to accelerate the separation of the electron hole rate.Including 8 compounds degradation effect is best,it is because the compound 8 has more {Mn(H2O)} unit,its has a channel layer structure and special interlayer space,increases the contact area of the substrate and the active material,per unit volume for the catalytic reaction to provide more redox active center,used the shortest possible time,therefore the degradation effect is best,but overall,basket type compound is relatively excellent photocatalyst.