Keggin-Type Polyoxometalate-Based Metal-Organic Networks for Photocatalytic Dye Degradation

• Published in: Chemistry, an Asian journal Vol. 10; no. 8; pp. 1676 - 1683
• Main Authors: Hao, Hong-Fang, Zhou, Wen-Zhe, Zang, Hong-Ying, Tan, Hua-Qiao, Qi, Yan-Fei, Wang, Yong-Hui, Li, Yang-Guang
• Format: Journal Article
• Language: English
• Published: Germany Blackwell Publishing Ltd 01.08.2015; Wiley Subscription Services, Inc
• Subjects: Benzene Derivatives - chemistry; Catalysis; Chemistry; Crystallography, X-Ray; Diffraction; Imidazoles - chemistry; metal-organic frameworks; Metals - chemistry; Methylene Blue - chemistry; Models, Molecular; Organometallic Compounds - chemistry; photocatalysis; Photolysis; polyoxometalates; rigid ligands; Tungsten Compounds - chemistry; X-rays; rigid ligands; photocatalysis; polyoxometalates; metal-organic frameworks
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201500424

The reaction of Keggin‐type polyoxometalate (POM) units, transition‐metal (TM) ions, and a rigid bis(imidazole) ligand (1,4‐bis(1‐imidazolyl)benzene (bimb)) in a hydrothermal environment led to the isolation of four new POM‐based metal–organic networks, [H2L][CuL][SiW12O40]⋅2 H2O (1), [H2L]2[Co(H2O)3L][SiW11CoO39]⋅6 H2O (2), KH[CuL]2[SiW11CoO39(H2O)]⋅2 H2O (3), and [CuL]4[GeW12O40]⋅H2O (4; L=bimb). All four compounds were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X‐ray diffraction, and single‐crystal X‐ray diffraction. Compounds 1 and 3 are new 3D networks with 1D channels. Compounds 2 and 4 contain 2D networks, which further stack into 3D supramolecular networks. The contributions of pH value, the negative charge of the POM, and the TM coordination modes to the construction of 3D networks were elucidated by comparing the synthetic conditions and structures of compounds 1–4. The photocatalytic properties of compounds 1–4 were investigated using methylene blue (MB) degradation under UV light. All compounds showed good catalytic activity and structural stability. The possible catalytic mechanism was discussed on the basis of active‐species trapping experiments. The different photocatalytic activities of compounds 1–4 were explained by comparison of the band gaps of different POM species and different packing modes of POM units in these hybrid compounds. POMs pack a punch: New polyoxometalate (POM)‐based metal–organic networks (see picture) were explored as active photocatalyts for dye degradation. Their catalytic properties are related to the band‐gap structures of POM species and the packing arrangements of POM units in the networks.