A Keggin-type polyoxomolybdate-based crystalline material formed by hydrothermal transformation: photo/electro-catalytic properties and mechanism study

Abstract

A Keggin-type polyoxometalate-based crystalline complex, [(SiMo₁₂O₄₀)Cu₆(2,2′-bipy)₆(Mo₆O₂₂)] (complex 1), has been prepared by using a Waugh-type polyoxometalate building block [MnMo₉O₃₂]⁶⁻, and for the first time, Waugh-type polyoxometalate was converted to a Keggin-type structure under hydrothermal conditions by using a Teflon-lined reactor with glass vials. The synthesized complex was characterized by single-crystal and powder X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, and elemental analysis. Structural characterization results show that complex 1 comprises Keggin-type [SiMo₁₂O₄₀]⁴⁻ anions and [Cu₆(2,2′-bipy)₆(Mo₆O₂₂)]⁴⁺ cation moieties composed of isopolymolybdates with 2,2′-bipy-coordinated copper ions, leading to a three-dimensional (3D) supramolecular network. This polyoxometalate assembly exhibits excellent photocatalytic properties and good cyclic stability for the photodegradation of methylene blue (MB) dye. In addition, the experimental results demonstrate that complex 1 also possesses outstanding electrocatalytic activity for nitrite reduction.