Design And Construction Of Polyoxometalate-based Metal-Organic Coordination Polymers For The Research On Hydrogen Peroxide Activation Performance

Hydrogen peroxide,H₂O₂,is an important inorganic compound.It has excellent redox activity and is widely used in medicine,environmental disinfection,sterilization,bleaching and so on.Especially in various physiological metabolic processes,it is one of the most important reactive oxygen species（ROS）.It is considered to be the messenger and marker of cellular signal transduction and pathological changes in a variety of cancers,Alzheimer’s disease and autoimmune diseases.Therefore,it is of great significance to establish and develop sensitive,rapid and accurate H₂O₂detection methods in the monitoring of human physiological data and the detection and diagnosis of diseases.In addition,H₂O₂is also a green and mild oxidant commonly used in chemical reactions.Its efficient and controllable activation is the key in catalytic oxidation.Aiming at the key scientific problems of efficient and rapid detection and activation of H₂O₂,in this paper we select polyoxometalate（POM）-metal-organic coordination polymers with rich,adjustable composition,redox and clear structure as the research object.Through hydrothermal synthesis,based on the self-assembly of classical Keggin,Dawson and preyssler POMs with different transition metals and nitrogen-containing organic ligands,four series of new POM-based metal-organic coordination polymers were designed and synthesized.Systematic research work was carried out from three aspects:horseradish peroxidase（HRP）immobilization,electrocatalytic H₂O₂detection and H₂O₂activated catalytic oxidation.The composition and structure of POMs,transition metals and organic ligands,as well as the structure-activity relationship of H₂O₂detection and activation were deeply explored.The main research contents and main research results are as follows:1.Using Dawson type tungstophosphate K₆[α-P₂W₁₈O₆₂]·14H₂O(abbreviated as K-{α-P₂W₁₈}),Zn SO₄·7H₂O and 2,2’-bisimidazole（H₂biim）as raw materials,two Dawson type POM-metal-organic coordination polymers were successfully synthesized under hydrothermal conditions in the pH range of 6.0-6.5:{[（Zn（H₂biim）₂）₃(P₂W₁₈O₆₂)]·6H₂O}_n（1）and[H₆（H₂biim）₆(P₂W₁₈O₆₂)]·8H₂O（2）.Compound 1 can be used as a carrier for the immobilization of horseradish peroxidase（HRP）by using the high electronegativity of Dawson type POM and the flexibility of metal organic complexes.Under the optimum loading conditions,it shows a high loading capacity for HRP(90.1 mg·g^-1).The POM-HRP composite has high oxidation catalytic activity in the model color reaction for the detection of H₂O₂,and its detection limit of H₂O₂is 3.11×10^-3mol·L^-1,and the enzyme has not been inactivated after 12 cycles.This work confirmed the feasibility of POM-metal-organic coordination polymer materials in the application of new enzyme carriers,and brought a new enlightenment for efficient and stable enzyme loading.2.Using Na-centered preyssler POM(abbreviated as{NaP₅W₃₀}),i.e.K_12.5Na_1.5[NaP₅W₃₀O₁₁₀]·15H₂O as a raw material,TM（TM=Mn,Co,Cu,Zn）cations and ligand 1,4-bis（1h-imidazol-1-yl）benzene（bimb）were introduced into the POM system under hydrothermal conditions.Four hybrid compounds（compounds 3-6）with extended structure based on Na-core preyssler{NaP₅W₃₀}were synthesized:（H₂bimb）₆H₄[（Mn（H₂O）₃）₂（μ-bimb）(Mn（H₂O）₄（Mn（H₂O）₅）_0.75（Mn（H₂O）₄）_0.25(Na（H₂O）P₅W₃₀O₁₁₀))₂]·30.5H₂O（3）,（H₂bimb）₃H₄[（Co（H₂O）₄）₂（μ-bimb）(Na（H₂O）P₅W₃₀O₁₁₀)]·10H₂O（4）,{[（Cu（Hbimb）（H₂O）（μ-bimb）Cu（Hbimb）（H₂O））（Cu（H₂O）₂（μ-bimb）Cu（H₂O）₂）(（Cu（H₂O）₂）_0.5（μ-bimb）（Cu（H₂O）₃）_0.5)H₂(Na（H₂O）P₅W₃₀O₁₁₀)]·12H₂O}_n（5）and（H₂bimb）₂[(（Zn（Hbimb）（H₂O）₂）_0.5)₂（Zn（Hbimb）（H₂O）₄）₂H(Na（H₂O）P₅W₃₀O₁₁₀)]·8H₂O（6）.When compounds 3-6 used as a non-enzymatic H₂O₂electrochemical sensors,they showed good electrocatalytic activity with high sensitivity and low detection limit.The minimum detection limit of compound 4 was 0.13 mmol·L^-1and the sensitivity was 4.35μA/(mmol·L^-1),the response time is 1 s.In addition,compound 4 shows a good electrochemical operation stability and anti-interference ability.This work provides a new choice for developing a promising electrochemical non enzymatic H₂O₂sensor using preyssler{NaP₅W₃₀}-based materials.3.Taking advantage of the particularity of{P₅W₃₀}crown-like ether structure,four new organic-inorganic metal-organic complexes with a Ag-core{Ag P₅W₃₀}were designed and synthesized by hydrothermal reaction with different metal salts and organic ligands bimb,using Ag⁺ions with electrocatalytic H₂O₂sensing activity instead of central Na⁺ions:（H₂bimb）₆H₈[(（Mn（H₂O）₃（μ-bimb））_0.5（Mn（H₂O）₄）（Mn（H₂O）₅）_0.5(Ag P₅W₃₀O₁₁₀))₂]·29H₂O（7）,[（Cu（Hbimb）（H₂O）₂（μ-bimb）Cu（Hbimb）（H₂O））（Cu（H₂O）₂（μ-bimb）Cu（H₂O）₃）(（Cu（H₂O）₂）_0.5（μ-bimb）（Cu（H₂O）₃）_0.5)H₂(Ag P₅W₃₀O₁₁₀)]·12.5H₂O（8）,（H₂bimb）₂H[（Zn（Hbimb）（H₂O）₄（Zn（Hbimb））（H₂O）₂）_0.5]₂(Ag P₅W₃₀O₁₁₀)]·12H₂O（9）and（H₂bimb）₃H₂[（Ag（H₂O）₂）_0.5(Ag（Hbimb）Ag（Hbimb）（μ-bimb）Ag（Ag（H₂O）₂）_0.5(Ag P₅W₃₀O₁₁₀))·7H₂O（10）.Compounds 7-10 also have excellent electrocatalytic H₂O₂-detection activity.Compound 10 shows the best H₂O₂detection activity,with a minimum detection limit of 0.30 mmol·L^-1and a sensitivity of 13.81μA/(mmol·L^-1),the response time is less than 1 s.This work further reveals the effects of POM and transition metals on the non-enzymatic H₂O₂electrocatalytic detection activity of POM-metal-organic complexes,which provides an important reference basis for the rational design and construction of POM-based non enzymatic H₂O₂sensing materials.4.A supramolecular compound{[（Co（μ-ttb）（H₂O）₃）₂][HBW₁₂O₄₀]·2H₂O}_n（11）based on Keggin-type[HBW₁₂O₄₀]^4-POM units,metal Co²⁺ions and organic coordination ligand 1,3,5-tri（1,2,4-triazol-1-ylmethyl）-2,4,6-trimethylbenzene（ttb）was successfully synthesized by the hydrothermal synthesis.Compound 11 showed the excellent catalytic activity for the selective oxidation of styrene with H₂O₂as an oxidant.Within 4 hours,the conversion of styrene was up to 98%,and the selectivity of the product benzaldehyde was 99%.The catalytic activity of compound 11 was 5 times higher than that of single POMs or transition metal ion Co²⁺.A series of comparative experimental studies show that the synergistic catalytic activation of H₂O₂by POMs and[Co（H₂O）₃]²⁺cation is the key to its high catalytic activity.This work brings a new hope for the design of POM-based H₂O₂heterogeneous oxidation catalyst.