Ionic Self-Assembly of Polyoxometalate–Dopamine Hybrid Nanoflowers with Excellent Catalytic Activity for Dyes

In this paper, new inorganic–organic hybrid nanoflowers consisting of a Weakley-type polyoxometalate Na9[EuW10O36]·32H2O (denoted as EuW10) and biomolecule dopamine (DA) were fabricated through a simple ionic self-assembly (ISA) method. The hybrid nanoflowers were fully characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy, Raman spectra, X-ray diffraction (XRD), and fluorescence spectra. We found that the electrostatic interaction and hydrogen-bonding interaction between EuW10 and DA favored the formation of the hierarchical flowerlike structure with hundreds of nanopetals and their morphologies could be controlled simply by tuning the ratio and respective concentrations of the components. Once forming EuW10/DA vesicles or nanoflowers, the fluorescence of EuW10 was quenched due to the hydrogen bonding between the ammonium group of DA and the oxygen atom of EuW10 that blocked the hopping of the d1 electron in EuW10. Interestingly, the calcinated nanoflower showed excellent decomposition efficiency toward the organic pollutants such as the dyes of methyl orange (MO) and rhodamine B (RhB). Moreover, the catalyst for MO can be reused at least 6 cycles with only a slight dropping of catalytic efficiency, suggesting their promising applications in the treatment of wastewater.