A Comprehensive Study on the Dye Adsorption Behavior of Polyoxometalate-Complex Nano-Hybrids Containing Classic β-Octamolybdate and Biimidazole Units

Six new hybrids based on β-[Mo(8)O(26)](4−) polyoxometalates, [Ni(H(2)biim)(3)](2)[β-Mo(8)O(26)]•8DMF(1); (DMA)(2)[M(H(2)biim)(2)(H(2)O)(2)][β-Mo(8)O(26)]•4DMF (M = Ni (2), Co (3)), DMA = dimethyl-ammonium, H(2)biim=2,2′-biimidazole); [M(H(2)biim)(DMF)(3)](2)[β-Mo(8)O(26)]•2DMF (M = Zn (4), Cu (5)); [(DMA)(2)[Cu(DMF)(4)][β-Mo(8)O(26)]•2DMF](n) (6), have been successfully synthesized and characterized. Compounds 2–5 show favorable capacity to adsorb methylene blue (MB) at room temperature, and they can selectively capture MB molecules from binary-mixture solutions of MB/MO (MO = Methyl Orange), or MB/RhB (RhB = Rhodamine B). Compound 3 can uptake up to 521.7 mg g(−1) MB cationic dyes rapidly, which perform the maximum adsorption in an hour among the reported materials as far as we know. The compounds are stable and still work very efficiently after three cycles. For compound 3, the preliminary adsorption mechanism studies indicated that the adsorption is an ion exchange process and the adsorption behavior of polyoxometalate-complex can be benefited from additional exchangeable protons in the complex cations.