Organic-inorganic Hybrid Assemblies Based On Ti- Substituded Polyoxometalates For Photocatalytic Dye Degradation

The design and synthesis of organic- inorganic hybrid materials based on polyoxometalates(POMs) and metal-organic units have been paid great attention in last two decades. The introduction of various POM units into the metal-organic coordination polymer systems have not only dramatically expanded the structural topologies of hybrid materials, but also endowed them new functionalities and potential applications in catalysis, adsorption, luminescent, electronic and magnetic materials. Recently, a concentrating research topic in this field is the exploration of new photocatalytic systems for the dye degradation. So far Keggin/Dawson-type POM-based hybrid complexes are one of the most developed catalyst systems for dye degradation. Thus, an ongoing challenging project in this research filed is chemically modulating the addenda atoms of POMs with different metal ions and setting them in a similar hybrid system so as to evaluate the photocatalytic activity of different POM species and select more active photocatalysts. Ti-substituted POMs(abbr. Ti-POMs) has ever been estimated as a potentially effective photocatalyst species based on the DFT calculation. Furthermore, H3PW12O40/Ti O2 composite materials have exhibited high photocatalytic activities in the degradation process. Therefore, the exploration of Ti-POM-based organic-inorganic hybrid compounds may suggest a new way to obtain active photocatalyst systems.Based on above consideration, we prepared three new organic- inorganic hybrid compounds, [N(CH3)4]6[CuIILo][(Ti2O)(PW11O39)2]·4H2O(1) [N(CH3)4]2[H2bpp]2[CuIILo][(Ti2O)(PW11O39)2]·1.5H2O(2) and [Cu(I)Lo]4[PW11Ti O40](3)(Lo = 1,2-bis(3-(2-pyridyl)pyrazole-1-ylmethyl)benzene, bpp = 1,3-bis(4-piperidyl)propane), based on Ti-substituted polyoxometalates(abbr. Ti-POMs) and the metal-organic linking units constructed by C uII or CuI ions and bichelate-bridging ligands(Lo), have been hydrothermally prepared. The three compounds were characterized by elemental analyses, IR spectra, TG analyses, XPS spectra, power X-ray diffraction and single-crystal X-ray diffraction analyses. Compound 1 and 2 contain a rare corner-sharing double-Keggin type POM architecture in the Ti-POM species. Compound 1-3 contain butterfly-type [C uIILo] units. In 1 and 2, the double-Keggin-type polyoxoanions connect with the butterfly- type [C uIILo] units to form a 1-D chain and a square plane, respectively. While in 3, the polyoxoanions act as template linking with butterfly- type [C uIILo] units to form a supermolecule. The photocatalytic properties of compounds 1-3 were investigated with the methylene blue(MB) degradation model under UV irradiation, indicating good photocatalytic activities. Furthermore, to compare the photocatalytic property of the Keggin-type Ti-POMs with those of traditional Keggin-type POMs, another compound [CuILo]4[PW12O40](4) was synthesized by combining typical Keggin- type polyoxoanio ns with the metal-organic [C uILo] units. A series of MB degradation experiments suggest that the Ti-POMs exhibit better photocatalytic activity than those of typical Keggin- type saturated POM species.