Preparation Of Ordered Structural Materials Of Polyoxomolybdate {Mo₇₂Fe₃₀}/DODMA At The Air/Water Interface

Nanoscale polyoxomolybdates (POMs) not only own well-defined geometrical structures, but also have many potential applications in catalysis, electrochemistry, biomedicine, sensors and magnetism, etc. Many POMs are quite soluble in polar solvents including water, ethanol and acetone. It is known that in aqueous solution, the main parts of the POM clusters exist as macroanions, balanced by small cationssuch as Na⁺, NH₄⁺ or H⁺. According to electrostatic interaction, polyoxomolybdatescan be modified by cationic surfactants into surfactant-encapsulated clusters (SECs) which are novel polyoxomolybdate-based organic/inorganic hybrid materials. In this paper, we detailly studied the formation of the ordered self-assembled structures and phase behavior from three points as follows:1. At first, we synthesized two Keplerate-type spherical Polyoxomolybdates {Mo₁₃₂} and {Mo₇₂Fe₃₀} according to the literatures. And the experimental data are consistent with the reported ones of the literatures. We tested the conductivity and pH values of the two clusters in aqueous solution and explore their basic physiochemical properties. The results show that {Mo₁₃₂} and {Mo₇₂Fe₃₀} both are weak electrolytes, and {Mo₇₂Fe₃₀} behaves like a weak acid in solution due to the partial deprotonation of the H₂O ligands attached to the Fe centers.2. We obtained the unprecedented highly ordered, uniform, reproducible honeycomb architectures at the air/water interface by evaporating organic solvent. The solvent-cast architectures of {Mo₍72_Fe₃₀}/DODMA complexes in organic medium were prepared at the air/water interface are studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). We studied the interactions between {Mo₇₂Fe₃₀} and cationic surfactant D0DMAC1 by ¹H NMR experiments.3. The phase behavior between Polyoxomolybdate ({Mo₁₃₂}, {Mo₇₂Fe₃₀}) and cationic surfactant TTABr (tetradecyltimethylammoniumbromid) in aqueous solution was studied. We tested the structures and electrochemical properties of the aggregates in solution by TEM and Zeta potential experiments. The mechanism of the whole phase transition is offered.