Nanocomposites Containing Keggin Anions Anchored on Pyrazine-Based Frameworks for Use as Supercapacitors and Photocatalysts

Designing highly active Keggin-anion anchored on pz-based frameworks is desirable but still a huge challenge. Herein, three new POM-based inorganic-organic hybrid compounds [{Ag-5(pz)(7)}(BW12O40)] (1), [{Ag-5(pz)(7)} (SiW12O40)]-(OH).H2O (2), (Hpyr)[{Ag(pz)}(2)(PMo12O40)] (3) (pz = pyrazine, pyr = pyrrole) have been fabricated via a hydrothermal synthesis method. All compounds were characterized by elemental analyses, infrared spectroscopy (IR), powder X-ray diffraction (PXRD), thermogravimetric (TG), scanning electron micrographs (SEM), and transmission electron microscope (TEM). Single-crystal X-ray diffraction displays that the configurations of compounds 1 and 2 are parallel. In compound 1, the [BW12O40](5-) is as 8-connected node incorporated into the orifice of the Ag-pz framework forming the glamorous POM-based metal-organic frameworks (POMOFs). And the 3D POMOFs possess a kind of novel topology {4(2)-5(4)}(2){4(4).5(12).68(.)7(3).9}{4(4).5(3).}. 6(3)}{4(4).5(8).6.74(.)9}{7(3)} There is a metal-organic nanotube structure constructed by four Ag-pz chains in compound 3. Then, the opened POMOFs consist of [PMo12O40](3-) clusters encircled in metal-organic nanotubes with the topology {3(4).4(6).5(4).6}(2){3(4).4(8). 5(8).6(4)-7(4)}. When used as electrode materials, as-prepared compounds 1, 2, and 3 have high specific capacitance of 1058, 986, and 1611 F g(-1) at a current density of 2.16A g(-1) and favorable cycling stability; after 1000 cycles, the retention rates of the capacitance are 90.3%, 94.5%, and 84.8% at 15.12 A g(-1) in supercapacitors, respectively. Moreover, the ability of compounds 1-3 to degrade dyes is excellent under UV irradiation. The degradation rates of RhB are 94.89% for 1, 93.06% for 2, and 96.88% for 3 after 150 min, and the degradation rates of MB are 96.48% for 1, 94.28% for 2, and 98.58% for 3 after 90 min. These results illustrate that compounds 1-3 have potential applications in energy functional materials and organic pollutant degradation.