Synthesis Of Polyoxometalates-based Compounds And Their Electrochemical Detection For Uric Acid And Dopamine

Objective:Shortcoming of polyoxometalates,such as weak electrical conductivity and low specific surface area,greatly limited the improvement of electrocatalytic activity,so new polyoxometalates-based crystalline compounds and polyoxometalates-based multicomplexes were synthesized by self-assembly of polyoxometalates,metal ions,rigid organic ligands,or ferrocene and graphene oxide.It is expected that novel polyoxometalates based compounds with convenience,low cost,high sensitivity and high selectivity can be obtained by systematic electrochemical detection of uric acid and dopamine.Methods:Crystalline polyoxometalates-based compound and ferrocene/graphene/polyoxometalates based ternary composites were synthesized by hydrothermal synthesis and characterized by X-ray single crystal diffraction,X-ray powder diffraction,X-ray photoelectron spectroscopy,Raman spectroscopy,scanning electron microscopy,elemental analysis,infrared spectroscopy and nitrogen adsorption.To evaluate the electrochemical activities of crystalline polyoxometalates-based compound and ferrocene/graphene/polyoxometalates based ternary composites to uric acid and dopamine,respectively.Electrochemical properties were studied by employing three-electrode system（glassy carbon electrode as the working electrode,platinum wire as the counter electrode and Ag/Ag Cl as the reference electrode）,and were performed by cyclic voltammetry,differential pulse voltammetry,alternating current impedance method and amperometric methods.Results:Five new polyoxometalates based compounds were successfully synthesized and molecular formulas follows as:Compound（1）:H₁₀[Cu（bix）₂(P₂W₁₈O₆₂)₂]（bix）₆·16H₂O(Cubix P₂W₁₈)Compound（2）:（H₂bix）₃(P₂W₁₈O₆₂)·H₂O(bix P₂W₁₈)Compound（3）:Fc（100mg）-r GO-PMo₁₂（r GFP-1）Compound（4）:Fc（50 mg）-r GO-PMo₁₂（r GFP-2）Compound（5）:Fc（150 mg）-r GO-PMo₁₂（r GFP-3）.The performances of the above five compounds were evaluated by electrochemical detection of biological small molecules.It was found that compounds 1 and 2 show excellent detection activities for uric acid molecules,and the detection range was2.5×10^-7～6.79×10^-4 M and 2.5×10^-7～6.99×10^-4 M,and the detection limits can reach4.97×10^-7 M and 2.56×10^-6 M,respectively.The compounds 3,4 and 5 showed excellent detection activity for dopamine molecules,among compound 3 had the largest current response,so compound 3 was selected for subsequent experiments,the detection range was 1.0×10^-7～9.3×10^-5 M,and the detection limit can reach 3.75×10^-7 M.Conclusion:In this work,five polyoxometalates-based compounds were successfully synthesized by hydrothermal synthesis.For the reason that the faster electron transfer and the more active centers provided by synergistic effects of P2W18、Cu-bix/bix subunits and the helical structure,the fabricated compound 1 and 2 exhibited better electrocatalytic activity toward the oxidation of UA.And hydrogen bonds and short interactions between protonated bix ligand and POM make a nonignorable contribution to the electrochemical response toward UA.By comparing the catalytic performance of the composites 3,4,5,we found that the electrocatalytic performance of the ternary composites is stronger than that of the binary composites and the simple substance because of the fast electron transfer rate of Fc,the larger surface area of r GO and the multi-electron redox of POM,the maximal synergy of Fc-r GO-PMo₁₂ and mass ratio of simple substance in one system contribute to the overall catalytic performance.