Nanocomposites and nanomaterials

Structural and morphological properties of ultrasonic-modified NiMoO4 hydrate 
Khemii M.M., Budzulyak I.M., Popovych O.M., Spodarenko R.H.
Vasyl Stefanyk Precarpathian National University, 57 Shevchenko St. Ivano-Frankivsk-76018, Ukraine
E-mail: maryahemiy@gmail.com

Ultrasonic modification is a promising method of controlled change in the particle size and the surface area of nanomaterials. We analyzed the crystal structure and morphology of nickel molybdate (NiMoO4) hydrate  obtained by hydrothermal method and modified by ultrasound (the operating frequency is 22 kHz) for 15, 60 and 90 minutes. 
According to the results of X-ray diffraction analysis, the average crystallites size, calculated by the Scherrer equation, was 17 nm for the initial nickel molybdate and for all modified samples. The morphological properties were investigated by the low-temperature nitrogen absorption / desorption porosimetry. IV hysteresis is observed for all materials (according to UIРАС classification) in the range P/P0 0.5–1.0. The specific surface area of the initial nickel molybdate was 31 m2/g and does not change for the modified materials (28-31 m2/g). The pore size distribution spectra determined by the Barrett – Joyner – Halenda method indicate the mesoporous structure of nickel molybdates and an increase in the average pore diameter from 17 nm for the initial nickel molybdate to 28.8 nm for material modified by ultrasound for 90 min. DFT (density functional theory) histograms indicate a wide pore size distribution in the range of 2-26 nm and an increase in total mesopores volume from 0.135 cm3/g to 0.223 cm3/g with prolonged ultrasonic dispersion. 
Thus, ultrasonic modification does not change the crystallite size of NiMoO4 hydrate, however, in modified materials there is a redistribution of pores in size, namely, the volume of mesopores with a diameter of 20-28 nm increases. This is due to the fact that at ultrasonic frequencies from 20 kHz to 50 kHz, the most common are physical effects, including shock waves, which accelerate solid particles suspended in the liquid, causing changes in the morphology of materials.