Investigation of the formation process of zeolite-like 3D frameworks constructed with ε-Keggin-type polyoxovanadomolybdates with binding bismuth ions and preparation of a nano-crystal

Reaction conditions for the synthesis of an epsilon-Keggin-type polyoxometalate-based 3D framework, (NH4)(2.8)H-0.9[epsilon-VMo9.4V2.6O40Bi2]center dot 7.2H(2)O (denoted as Mo-V-Bi oxide), are studied. It is found that the reaction time, temperature, pH of the solution, and starting compounds affect the production of Mo-V-Bi oxide. The crystal size of Mo-V-Bi oxide is controllable by changing bismuth compounds. Nanometer-sized Mo-V-Bi oxide is produced using a water-soluble bismuth compound, Bi(NO3)(3)center dot 5H(2)O, whereas micrometer to submicrometer-sized Mo-V-Bi oxide is produced using Bi(OH)(3), which is less soluble in water. The particle size of the material affects the properties of the material, such as surface area and catalysis. The investigation of the formation process of the material is carried out with Raman spectroscopy, which indicates that mixing (NH4)(6)Mo7O24 center dot 4H(2)O, VOSO4 center dot 5H(2)O, and bismuth ions in water produces the epsilon-Keggin polyoxovanadomolybdate together with a ball-shaped polyoxovanadomolybdate, [Mo72V30O282(H2O)(56)(SO4)(12)](36-) (denoted as {Mo72V30}). By heating the reaction mixture, the epsilon-Keggin polyoxovanadomolybdate assembles with bismuth ions to form Mo-V-Bi oxide, whereas {Mo72V3O} assembles with other vanadium and molybdenum ions to form orthorhombic Mo-V oxide.