Preparation And Properties Of Keggin Type Cluster-Based Functional Materials

Polyoxometalates（POMs）are generally polynuclear clusters with unique structures and sizes composed of group VB and VIB transition metals(e.g.,V⁵⁺,Nb⁵⁺,Mo⁵⁺and W⁵⁺)and oxygen atoms,which occupy a very important position in metal-oxygen cluster science.As one of important branch of cluster science,Keggin type cluster-based functional materials exhibit excellent performance and wide applications in catalysis,medicine and sensing and so on due to their unique topology,photosensitivity,good thermal and chemical stability,and the ability of reversible multielectron redox ability.In this paper,oxides or salts of cluster-forming elements（W,V and Sb）,nitrogen-containing organic ligands and transition metal salts were selected for reaction under hydrothermal conditions,and five Keggin-type cluster-based functional materials with novel structures and excellent properties were obtained by controlling the reaction conditions.The crystal structures were determined by X-ray single-crystal diffraction and characterized by elemental analysis,IR,XRD,XPS,TG,etc.The structural formulae of the five Keggin-type cluster-based functional materials are as follows:1.[Cu₂（2,2’-H₂bpy）₄Cl]{[Cu（2,2’-H₂bpy）₂][BW₁₂O₄₀]}·2H₂O（1）2.[Cu（Amitrole）]₆[PW₁₂O₄₀]₂·H₂O（2）3.{[Ni（2,2’-bpy）₂（H₂O）]₂[H₃W₁₂O₄₀]}[Ni（2,2’-bpy）₃]_0.5·H₂O（3）4.{[Cu（2,2’-bpy）₂]₂[BW₁₂O₄₀]}[Cu（2,2’-bpy）]_0.5·H₂O（4）5.H₁₆[Si V₁₂O₄₀]·H₂O（5）（2,2’-bpy=2,2’-bipyridine,Amitrole=3-amino-1,2,4-triazole）.Compound 1 is a three-dimensional supramolecular compound composed of a transition metal complex cation mono-supported cluster anion{[Cu（2,2’-H₂bpy）₂]-[BW₁₂O₄₀]}³⁺,a halogen cluster[Cu₂（2,2’-H₂bpy）₄Cl]³⁺and a water molecule.Compound 2 is a novel POM-TMCs-POM type dimer consisting of a cyclic[Cu₆（Amitrole）₆]⁶⁺complex cation covalently linked to two cluster anions[PW₁₂O₄₀]^3-.Compound 3 is composed of[Ni（2,2’-bpy）（H₂O）]²⁺andα-Keggin cluster anion[H₃W₁₂O₄₀]^5-forming a mono-supported structure[H₃W₁₂O₄₀][Ni（2,2’-bpy）₂（H₂O）]^3-.Compound 4 is a bi-supported structure of{[Cu（2,2’-bpy）₂]₂[BW₁₂O₄₀]}^2-formed by two Cu²⁺-2,2’-bpy complex cations with cluster anion[BW₁₂O₄₀]^5-.Compound 5 is an inorganic acid with high symmetry consisting of a Keggin-type cluster[Si V₁₂O₄₀]^16-and a water molecule,and the crystals exhibit a body-centered cubic stacking mode.The synthesis law of cluster-based hybrid materials was preliminarily explored,and the effects of the selection and proportioning of raw materials,reaction system p H,reaction time and temperature on the formation and structure of the materials were investigated.The photocatalytic properties of cluster-based materials 1-5 were investigated by using rhodamine B（Rh B）and methylene blue（MB）to simulate organic pollutants in industrial wastewater.After 120 minutes of reaction,using compounds 1-4 as catalysts,the degradation rates of pure MB solution were 99%,83.8%,98.5%,and 82.5%,respectively;The degradation rates of pure Rh B solution were 51%,60.7%,64.8%,and 43.3%,respectively;In the mixed solution of Rh B+MB,the lowest photodegradation rate of MB is 82.5%,the highest is 99%,and the lowest photodegradation rate of Rh B is 32.2%,the highest is 80%.The results show that compounds 1-4 are good photocatalysts,and their photodegradation rate of MB is better than Rh B;Compared with the photocatalytic experimental results of compound 5,its catalytic effect on Rh B is relatively poor,with the highest catalytic efficiency of only 20.2%.The chemical catalytic properties of compounds 1-5 were verified using styrene epoxidation reactions,with compound 4 exhibiting a conversion rate of 93.94%for styrene,demonstrating good chemical catalytic performance.In addition,preliminary studies on the fluorescence properties of DMSO solutions of compounds 1-4 were carried out.