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In this paper, structural features of the NiO-SiO2 nanocrystalline catalyst synthesized by the sol-gel method were studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (TEM), and differential dissolution (DD). The XRD pattern of NiO-SiO2 significantly differs from the "ideal" NiO pattern: the peaks of the NiO-like phase are asymmetric, especially the 111 diffraction peak. The NiO-SiO2 nanocrystalline catalyst was investigated by means of XRD simulations based on two approaches: conventional Rietveld analysis and statistical models of 1D disordered crystals. Through a direct simulation of XRD profiles, structural information is extracted from both the Bragg and diffuse scattering. XRD simulations showed that the asymmetry of all the diffraction peaks is due to the presence of two NiO-like oxides with different lattice constants and different average sizes: ~90 wt% of mixed Ni-Si oxide (Ni:Si = 0.14:0.86) with average crystallite sizes (D ~ 27.5 Å) and ~10 wt% of pure NiO (D ~ 50 Å). The high asymmetry of the 111 diffraction peak is due to the appearance of diffuse scattering caused by the inclusion of tetrahedral SiO2 layers between octahedral NiO layers. Such methods as TEM and DD were applied as independent criteria to prove the structural model, and the results obtained confirm the formation of mixed Ni-Si oxide. [ABSTRACT FROM AUTHOR]

In the recent decade, various potential applications of the luminescence of nanosized ZrO 2 :Eu3+ have been demonstrated. However, the particle size effect on the luminescence properties of ZrO 2 :Eu3+ still requires intensive investigation. To this end, a series of tetragonal ZrO 2 :Eu3+ nanopowders with the europium concentration of 4 wt% and particle size of 3.0 ± 0.7 to 12.0 ± 4.8 nm was synthesized by laser vaporization. It was shown that the dominant role in the optical properties of ZrO 2 :Eu3+ nanoparticles belongs to OH groups, oxygen vacancies, and Eu3+ ions. It was found that a decrease in the particle size is accompanied by a significant increase in the emission intensity in the region of ∼440 nm. Based on the results of thermal analysis, IR and UV–vis DR spectroscopies, it was concluded that this luminescence is due to the emission of adsorbed OH groups. At the same time, a decrease in the number of vacancies with a decrease in the particle size leads to a change in the absolute quantum yield QY from ∼7 to 3.5%. In addition, despite the overall decrease in the intensity of the red luminescence of Eu3+, a decrease in the particle size leads to the appearance and increase in the emission intensity of the surface Eu3+. Thus, changing the particle size from 12.0 to 3.0 nm leads to a twofold decrease in the luminescence efficiency of ZrO 2 :Eu3+ and a shift in the color of its emission from pink-red (0.36, 0.26) to blue (0.19, 0.10). The results obtained are expected to be useful for further optimization of the luminescence properties of nanosized ZrO 2 :Eu3+ in numerous applications. [ABSTRACT FROM AUTHOR]

X-ray diffraction (XRD) pattern of nanosized equimolar solid solution CoIr prepared by thermolysis of [Co(NH3)6][Ir(C2O4)3] contains peaks characteristic of both face-centered cubic (fcc) and hexagonal close-packed (hcp) structure. Moreover, 101 peak of hcp modification is substantially wider than 100 and 002 peaks, 102 and 103 are very broad and almost invisible. Peak 200 of fcc structure is wider than the other peaks of this modification and slightly shifted toward lower angles. It was shown by simulation of XRD patterns that particles of CoIr alloy are nanoheterogeneous and consist of lamellar domains having fcc and hcp structures. The best fit was obtained for the following model parameters: an average crystallites size is about 10 nm, average thicknesses of the fcc and hcp domains are 1.7 and 1.1 respectively. The presence of domain structure was confirmed by transmission electron microscopy data. [ABSTRACT FROM AUTHOR]

Laser vaporized xCr/Al 2 O 3 nanopowders with the particle size of ca. 15 nm were studied by XRF, EDX, HRTEM, XRD, DD, BET, TGA, UV–Vis DRS, Raman and PL spectroscopy methods as a catalytic system in dehydrogenation of isobutane. The nanopowders were found to contain not only the Cr6+ ions located on the surface of nanoparticles, but also two different types of Cr3+ sites as components of the γ-Al 2 O 3 solid solution. One type consists of the bulk Cr3+ b sites in a strong crystal field. Another type is represented by the Cr3+ s sites residing near the surface of xCr/Al 2 O 3 nanoparticles. Such sites are in a weak crystal field. It was shown that catalytic activity of the nanostructured xCr/Al 2 O 3 system is provided by the high content of surface Cr3+ s sites. The results obtained make it possible to propose the nanopowders obtained by laser synthesis as a promising catalytic system that can be used in the development of highly active catalysts for dehydrogenation of alkanes with the decreased chromium content. Unlabelled Image • Model CrO x /Al 2 O 3 nanoparticle catalysts were obtained by laser vaporization • Structure, morphology and optical properties of CrO x /Al 2 O 3 nanopowders were studied • Cr3+ s sites are located near the surface of CrO x /Al 2 O 3 nanoparticles • Cr3+ s sites play the key role in the isobutane dehydrogenation reaction • CrO x /Al 2 O 3 nanoparticles are highly active catalysts with the decreased Cr content [ABSTRACT FROM AUTHOR]

Nanosized Eu/γ- and/or η-Al 2 O 3 ([Eu 2 О 3 ] = 0.00, 0.02, 0.45 and 0.92 wt%) powders with the particle size from <10 nm to 21 nm synthesized by cw CO 2 laser vaporization were studied. It was shown that photoluminescence (PL) properties of the obtained samples are caused by luminescence of the Eu3+ and Eu2+ ions incorporated to the Al 2 O 3 matrix in crystallographic positions with the C 3v local symmetry. A scheme based on the formation of Eu2+ ions in the Al 2 O 3 lattice via the charge compensation by oxygen vacancies (F centers) located in the first coordination sphere of europium was proposed. The influence of size effects on PL of Eu/Al 2 O 3 nanoparticles consists first of all in shortening the lifetime of 4f – 4f transitions in Eu3+ ions as a result of increased probability of nonradiative relaxation owing to OH groups and various structural defects. It was found that the conditions of laser vaporization (gas composition and pressure) can change the structure of the resulting Eu/Al 2 O 3 nanoparticles. Image 1 • Nanoparticles of Eu/Al 2 O 3 with the particle size from <10 nm to 21 nm were synthesized by cw CO 2 laser vaporization. • Eu3+ and Eu2+ ions were detected by PL in Eu/Al 2 O 3 nanoparticles. • Eu3+ and Eu2+ ions incorporated to the Al 2 O 3 matrix in crystallographic positions with the C 3v local symmetry. • Size effects on lifetime of 4f – 4f transitions in Eu3+ ions were detected. [ABSTRACT FROM AUTHOR]