| Polyoxometalates(POMs)are a class of compounds formed by condensation and dehydration of simple oxometalates under certain pH conditions.POMs have the advantages of high stability,rich structure and strong electron transport capacity.They are widely used in photocatalysis,sensing and energy storage.[P2W18O62]6-is one of the important members of Dawson type POMs.Its unique chemical structure makes it have more complex coordination mode and better redox performance.However,this kind of structure has larger steric hindrance,and the traditional hydrothermal synthesis method is more difficult because of its low efficiency.Therefore,it is still a great challenge to explore efficient and simple synthetic methodsIn this paper,K6[P2W18O62]was used as the precursor,and two compounds were synthesized by hydrothermal method,which using imidazole and 4,4'-bipyridine as ligands and adjusting pH.The chemical formulas(H2imi)3[P2W18O62](1)and(4,4'-H2bipy)2(4,4'-Hbipy)2[P2W18O62](2)were determined by elemental analysis and TG analysis.Single crystal diffraction analysis indicates that both compounds are supramolecular compounds,which form 1D-3D structures through?-?stacking and supramolecular interaction.The supercapacitor performance was tested for compounds1 and 2 as electrode materials and foam nickel as the collector.When the current density is 1A/g,the specific capacitance of the three electrode system is 246.7F/g and 249.1F/g respectively.The energy density and power density of the symmetrical supercapacitor are 6.8Wh/kg,6.4Wh/kg and 394.1W/kg,312.1Wh/kg respectively.In addition,the photocatalytic degradation properties and H2O2sensing properties of compounds 1 and2 were also studied.The photocatalytic degradation rates of methylene blue(MB),Rhodamine B(Rh B)and methyl orange(MO)were 91.2%,90.5%,77%and 90.1%,87.8%,72%respectively.As a sensing material,the detection limits were 3.85×10-9mol/L(S/N=3)and 4.67×10-9mol/L(S/N=3),and the detection ranges were5?M-0.22m M,7.5?M-0.19m M,respectively.Four nanohybrids Mn[P2W18O62]m-M-BTC(M=Ag(3),Cu(4),Co(5),Ni(6))and their corresponding polyoxometalates Mn[P2W18O62]mand metal organic framework M-BTC were synthesized by grinding method.The compounds were characterized by IR,XRD,SEM,TEM and XPS,the supercapacitor and sensing properties were studied.In the three electrode system,the specific capacitance of compounds 3-6 were 381.4F/g,260F/g,269.7F/g,465.2F/g at the current density of 1A/g,and the resistance were3.09?,2.71?,3.29?and 3.16?respectively.The capacitance retention are 90.3%,92.4%,90.6%,93.3%after 5000 cycle,respectively.These results are superior to the corresponding polyoxometalate monomers and metal organic frameworks,indicating that the combination of metal organic frameworks can increase the dispersion and stability of polyoxometalates,thus improving the electron transport rate and lifetime of compounds.The energy densities of compounds 3-6 were 7.6 Wh/kg,3.2 Wh/kg,6.5Wh/kg and 20.9 Wh/kg,respectively,and the power densities were 494.7 W/kg,397.2W/kg,451.6 W/kg and 838.1 W/kg,respectively.In addition,in order to further explore the application of the hybrid compounds,the sensing properties of compounds 3-6 for hydrogen peroxide were tested.The detection limits were 4.23×10-9mol/L(S/N=3)?4.34×10-9mol/L(S/N=3)?4.62×10-9mol/L(S/N=3)?4.52×10-9mol/L(S/N=3)respectively in the linear range of 5?M-0.25m M.After 1000 CV cycles,the CV curves of compounds 3-6 did not change significantly,indicating that compounds 3-6 have excellent sensitivity and stability,indicating that compounds 3-6 have great potential in electrochemical sensing. |
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