The possibilities of mechanochemical activation as a successful route for direct synthesis of NiWO4 have been studied. A stoichiometric mixture of NiO and WO3 in a 1:1 molar ratio was subjected to intense mechanical treatment in air using a planetary ball mill for different periods of time. The phase and structural transformations were monitored by X-ray diffraction (XRD), infrared spectroscopy (IR), and X-ray photoelectron spectroscopy (XPS). It was found that 7.5 h of milling of the reagents leads to complete crystallization of single nanostructured phase NiWO4 at room temperature.

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Mechanochemistry H 3000Mechanochemical Synthesis of Nanocrystalline Nickel Molybdates. -NiMoO4 catalysts are prepared from 1:1 mixtures of NiO and MoO3 by intense mechanical treatment in air using a planetary ball mill for different periods of time ranging from 2.5 to 5 h. The samples are characterized by XRD, IR, and XPS. Single-phase α-NiMoO4 is obtained after 5 h milling at room temperature. Mechanochemical activation for 2.5 h results in the high-temperature β-NiMoO 4 phase. -(KLISSURSKI, D.; MANCHEVA*, M.; IORDANOVA, R.; TYULIEV, G.; KUNEV, B.; J. Alloys

Metastable orthorhombic (γ) ZrW2O8 was obtained by fast cooling of the melt of a stoichiometric mixture of ZrO2 and WO3. Heating of the as-quenched sample at 600 °C for 15 h led to the full transition of the orthorhombic (γ) to the cubic (α) ZrW2O8 polymorph. The average crystallite sizes of the obtained ZrW2O8 phases were in the range of 50−80 nm. The morphology of the powdery products was characterized by scanning electron microscopy.

ZrMo2O7(OH)2·2H2O was obtained from ZrOCl2·2H2O and Na2MoO4·2H2O by a coprecipitation method. The phase and structural changes occurred during the heat-treatment of ZrMo2O7(OH)2·2H2O were investigated by XRD, IR and XPS analysis. The sequence of phase transformation can be divided into three stages: (1) transformation of ZrMo2O7(OH)2·2H2O to orthorhombic LT-ZrMo2O8 up to 300°C; (2) obtaining of mixture of both polymorphs of ZrMo2O8: cubic and trigonal at 400°C; (3) conversion to single trigonal (α) ZrMo2O8 above 450°C. The microstructure of the obtained trigonal (α) ZrMo2O8 was observed by scanning electron microscopy (SEM). The particle sizes were below 0.5 µm. The specific surface area was measured by modified BET method. The photocatalytic activity of the obtained trigonal (α) ZrMo2O8 powders was investigated by degradation of a model aqueous solution of Malachite Green (MG) upon UV-light irradiation.

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