Studies On The Preparation And Properties Of Rare Metal Complexes/Titanate Compounds Based On Zirconium-containing Sandwich-type Heteropolytungstates

Polyoxometalates（POMs）are regarded as one of the excellent building blocks due to their nano-size,unique structural variety and interesting physicochemical properties,which have potential applications in the fields of photochemistry,electronic,magnetic and solid acid catalytic materials.As an important part of POMs,high-nuclearity heteropolytungstate clusters have received much attention in recent years.The introduction of transition metals（such as Fe,Co,Ni,Cu,and Zn）to obtain novel sandwich-type heteropolytungstate compounds with novel structures and excellent properties has attracted widespread attention from many scholars.Although zirconium-containing sandwich-type heteropolytungstates show excellent catalytic performance in the field of photochemistry and organic catalysis,there is no example of three-dimensional rare earth metal-organic framework based on zirconium-containing sandwich-type heteropolytungstates.At the same time,the composite material of zirconium-containing sandwich-type heteropolytungstates and titanate has not been reported,either.In this paper,eight POM-based rare earth metal-organic frameworks 1-8 and six titanate complexes based on POMs were synthesized by hydrothermal method and characterized by IR,UV spectroscopy,elemental analysis,XRPD and single-crystal X-ray diffraction analysis,where POM is the zirconium-containing sandwich-type heteropolytungstate and the organic ligand is pyridinedicarboxylate.The photocatalytic properties and organic catalytic properties of the related products were investigated.The contents of this paper are divided into three chapters:1 Eight new POM-based rare earth metal-organic frameworks 1-8 were synthesized by hydrothermal method with[(PW₉O₃₄)₂Zr₃]^9-as building blocks.According to the organic ligand,they are divided into the following two sections:（1）Four POM-based rare earth metal-organic frameworks 1-4 were synthesized from 3,5-pyridinedicarboxylic acid liangd and Na₉[(PW₉O₃₄)₂Zr₃]and Ln（NO₃）₃（Ln= La,Ce,Pr,Nd）.H{La₄（L¹）2（H₂O）₂₁[Zr₃（OH）₃(PW₉O₃₄)₂]}·15H₂O（1）H {Ce₄（L¹）₂（H₂O）₂₁[Zr₃（OH）₃(PW₉O₃₄)₂]} ·15H₂O（2）H{Pr₄（L¹）₂（H₂O）₂₁[Zr₃（OH）₃(PW₉O₃₄)₂]}·15H₂O（3）H {Nd₄（L¹）2（H₂O）₂₁[Zr₃（OH）₃(PW₉O₃₄)2]}·15H₂O（4）Singel-crystal X-ray diffraction analysis reveals that the structures of 1-4 exhibit novel 3D POM-based rare earth metal-organic frameworks constructed by the coordination interactions between the polyoxoanions[(PW₉O₃₄)₂Zr₃]^9-,as sexadentate ligands,and rare earth ions,and that of Ln-3,5-pydc species and rare earth ions.The Eg of compounds 1-4 is 3.44,3.44,3.49 and 3.58eV,respectively,indicating the broad band semiconductor properties of the compounds.Photocatalytic measurement shows that 1-4 can accelerate the photodegradation of RhB.In addition,compounds 1-4 have good performance on adsorption and photocatalytic degradation for MB.The adsorption capacity of compounds 3 and 4 reached to 177.7 mg·g^-1 and 188.1 mg·g^-1,respectively,and the photodegradation rate can achieve 94.7%and 85.1%.The catalytic experments showed that compounds 1-4 have good selective catalytic effects on o-methylbenzaldehyde and p-methylbenzaldehyde.The conversion rates of p-methylbenzaldehyde were 79.8%for 1 after 8 h,and the conversion rates of o-methylbenzaldehyde reached to 82.4%for 3 after 5 h.（2）Four POM-based rare earth metal-organic frameworks 5-8 were synthesized from 2,6-pyridinedicarboxylic acid liangd,Na₉[(PW₉O₃₄)₂Zr₃]and Ln（NO₃）₃（Ln= La,Ce,Pr,Nd）.Na{La₄（L²）₂（H₂O）₁₆[Zr₃（OH）)3(PW₉O₃₄))2]} · 19H)2O（5）Na{Ce)4（L²）2（H₂O）₁₆[Zr₃（OH）)₃(PW₉O₃₄))₂]} · 19H)₂O（6）Na{Pr₄（L²）₂（H₂O）₁₆[Zr₃（OH）₃(PW₉O₃₄)₂]} ·19H₂O（7）Na{Nd₄（L²）₂（H₂O）,6[Zr₃（OH）₃(PW₉O₃₄)₂]} · 19H₂O（8）Compounds 5-8 are basically isostructural and feature a 3D POM-based metal-organic framework,which formed through the coordination interaction of Ln,2,6-pyridinedicarboxylic acid and[(PW₉O₃₄)₂Zr₃]₉.The Eg of compounds 5-8 are 3.51,2.86,3.47 and 3.45eV,respectively.The results showed that compounds 5-8 have good adsorption properties for methylene blue.The adsorption rate of compounds 5-8 are 100%（5,20 min）,98.3%（6,25 min）,100%（7,10 min）and 98.9%（8,20 min）,respectively.The studies on catalytic reactions showed that the catalytic behaviors of compounds 5-8 are similar with compounds 1-4.The conversion rates of p-methylbenzaldehyde was 85.01%for 5 after 6 h,and the conversion rates of o-methylbenzaldehyde reached to 74.3%over for 7 after 2 h.2 Titanate complexes based on zirconium-containing sandwich-type heteropolytungstate 9-14 were synthesized.They are NTA-（PW₉）₂Zr₃-80（9）,NTA-（PW₉）₂Zr₃-100（10）,NTA-（PW₉）₂Zr₃-120（11）,NTA-(SiW₁₀)₂Zr₂-80（12）,NTA-(SiW₁₀)2Zr₂-100（13）and NTA-(SiW₁₀)₂Zr₂-120（14）.Photocatalytic measurement shows that 10 and 13 can effectively accelerate the photodegradation of RhB with the degradation rates of 80.6%（30 min）and 92.4%（60 min）,respectively.9 and 11 have obvious catalytic activities for photodegradation of methylene blue.The photocatalytic degradation rates were 84.8%and 85.9%,respectively.compound 13 has a catalytic activity on the oxidation of alkenes.In addition,the studies of cyclooctene epoxidation reaction catalyzed by 9-14 showed that the catalytic activities of 12-14 are better than the single NTA or polyoxometalate Cs10[(SiW₁₀O₃₆)₂Zr₂].The catalytic production rate reached 64.9%for 12 after 11 h.