Accurate lattice parameters from 3D electron diffraction data. I. Optical distortions

Determination of lattice parameters from 3D electron diffraction (3D ED) data measured in a transmission electron microscope is hampered by a number of effects that seriously limit the achievable accuracy. The distortion of the diffraction patterns by the optical elements of the microscope is often the most severe problem. A thorough analysis of a number of experimental datasets shows that, in addition to the well known distortions, namely barrel-pincushion, spiral and elliptical, an additional distortion, dubbed parabolic, may be observed in the data. In precession electron diffraction data, the parabolic distortion leads to excitation-error-dependent shift and splitting of reflections. All distortions except for the elliptical distortion can be determined together with lattice parameters from a single 3D ED data set. However, the parameters of the elliptical distortion cannot be determined uniquely due to correlations with the lattice parameters. They can be determined and corrected either by making use of the known Laue class of the crystal or by combining data from two or more crystals. The 3D ED data can yield lattice parameter ratios with an accuracy of about 0.1% and angles with an accuracy better than 0.03◦

Preparation of silver-montmorillonite nanocomposites by reduction with formaldehyde and borohydride

Na-rich montmorillonite (MMT) was intercalated with silver cations, which were subsequently reduced with formaldehyde or sodium borohydride. The silver-montmorillonite nanocomposites were studied by UV-visible spectrometry, transmission electron microscopy (TEM) and X-ray diffractometry (XRD). The influence of different reducing agents on the dispersity and size of silver particles deposited on montmorillonite surface was investigated. The reduction with borohydride gives rise to uniformly dispersed silver particles with a narrow particle size distribution from 3 nm to 13 nm. Formaldehyde reduction forms unevenly dispersed particles with a much wider size distribution, ranging from 3 to 100 nm. In addition, some Ag2O particles were found among silver particles prepared with formaldehyde, likely as a result of incomplete reduction. Silver-montmorillonite composites prepared by reduction with borohydride and formaldehyde contain 2.4 wt% and 5.3 wt% of Ag, respectively

Morphology and structure of silicalite-1 crystals. Evidence of twinning by X-ray and electron diffraction

Silicalite-1 was grown hydrothermally ill two batches with crystals 2-3 and 200-250 mu m in length. Small crystals are penetrating overgrowths with a cruciform cross section, large crystals are typical columns known from the literature. X-ray and electron diffraction show the material to be orthorhombic, with the Pnma space group and unit Cell a = 20.0801(2) angstrom, b = 19.9239(2) angstrom, c = 13.41 67(1) angstrom. silicalite-1 is ubiquitously twinned on (110), and thus all four prominent vertical crystal faces oil the large columnar crystals belong to the form {100}. In early stages of their growth, the untwinned crystals are tabular on (010) and elongated along [001], with prominent crystal forms {010), {100}, and {101}. Etching of large crystals with diluted HF and optical examination of the material in polarized light offer all explanation Of the hourglass structure and provide new clues about the growth process

Preparation and characterization of ZnS nanoparticles deposited on montmorillonite

ZnS nanoparticles were prepared and deposited on montmorillonite (MMT) in the presence of cetyltrimethylammonium (CTA). UV spectrometry and transmission electron microscopy (TEM) proved the formation of nanoparticles with diameters ranging from 3 nm to 5 nm. Selected-area electron diffraction (SAED) patterns revealed the presence of romboedric ZnS. The band gap energy of nanosize ZnS was estimated at 3.89 ± 0.03 eV. Photoluminescence spectra exhibited a strong emission band between 300 nm and 600 nm explained by the vacant ZnS nanostructure. The prepared ZnS–montmorillonite nanocomposite (ZnS–MMT) was used for the photocatalytic reduction of CO2 providing a considerably high efficiency that exceeded 5–6-fold the results of commercial TiO2 Degussa P25. The main reaction products were hydrogen and methane. Methanol and carbon oxide were also observed in about 7-fold lower amounts. The stability of ZnS against oxidation was confirmed by the determination of sulphate using capillary isotachophoresis

Characterization of silver nanoparticles deposited on montmorillonite

Silver nanoparticles were prepared by reduction of silver ions intercalated into montmorillonite (MMT) with borohydride and formaldehyde. They were deposited on the external surface of the MMT particles. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and specific surface area (SSA) measurements revealed that borohydride produced very small particles with narrow size distribution (3–13 nm) evenly dispersed on the MMT surface. Silver ions reduced by formaldehyde formed both small particles and large aggregates. The Ag nanoparticles were composed of cubic and hexagonal and/or amorphous silver crystals. The Raman scattering (SERS) was significantly increased by montmorillonite covered with Ag nanoparticles, especially when prepared with borohydride

Influence of the Ti microstructure on anodic self-organized TiO2 nanotube layers produced in ethylene glycol electrolytes

The relationship between the microstructure of Ti substrates and the anodic growth of self-organized TiO2 nanotube layers obtained upon their anodization in the ethylene glycol based electrolytes on these substrates is reported for the first time. Polished Ti sheets with mirror-like surface as well as unpolished Ti foils were considered in this work. Grains with a wide range of crystallographic orientations and sizes were revealed by Electron Backscatter Diffraction (EBSD) and correlated with nanotube growth on both types of substrates. A preferred grain orientation with [0 0 0 1] axis perpendicular to the surface was observed on all substrates. Surfaces of all substrates were anodized for 18 h in ethylene glycol electrolytes containing 88 mM NH4F and 1.5% water and thoroughly inspected by SEM. By a precise comparison of Ti substrates before and after anodization, the uniformity of produced self-organized TiO2 nanotube layers was evaluated in regard to the specific orientation of individual grains. Grains with [0 0 0 1] axis perpendicular to the surface turned out to be the most growth-promoting orientation on polished substrates. No orientation was found to be strictly growth-retarding, but sufficient anodization time (24 h) was needed to obtain uniform nanotube layers on all grains without remnant porous initial oxide. In contrast with polished Ti sheets, no specific orientation was found to significantly promote or retard the nanotube growth in the case of unpolished Ti foils. Finally, the difference between the average nanotube diameters of nanotubes grown on various grains was investigated showing non-negligible differences in the diameter for different grain orientations and substrates

Zelena logistika u kontekstu održivog razvitka u malim i srednjim pogonima

Forestry and wood-processing industry are sectors based on renewable ecological natural resources of wood raw material. Wood mass processing should be based on sustainable development, which involves the economic and social development based on environment preservation. Green logistics, which leads to change in creating the product value, characterizes different possibilities to measure and minimize the ecological impact of logistics activities and puts emphasis on sustainable ecological orientation, is closely related to sustainable development. The aim of this article is to investigate the issue of green logistics of forestry and wood processing in small and medium enterprises in Slovakia. To reach this goal, an empirical research was carried out, the objective of which was to determine the level of understanding, as well as the implementation of green logistics activities, and to identify its potential for future implementation in small and medium enterprises in selected branches. The research has revealed that as many as 28.8 % of enterprises claim not to have had any experience with green logistics within their enterprise. The greatest barrier for the implementation of green logistics appears to be the high input costs, which was confirmed by 62 % of the enterprises. On the basis of the research results, a model of implementation of green logistics concept in Slovak small and medium forestry and wood-processing enterprises has been proposed, as an element of sustainable development.Šumarstvo i drvoprerađivačka industrija u Slovačkoj sektori su koji se temelje na obnovljivim, ekološkim, prirodnim resursima, odnosno na drvu kao osnovnoj sirovini. Prerada drvne mase trebala bi biti osnova održivog razvoja, što podrazumijeva ekonomski i socijalni razvoj utemeljen na očuvanju okoliša. Zelenu logistiku, koja donosi promjene u određivanju vrijednosti proizvoda, karakteriziraju različite mogućnosti mjerenja i smanjenja utjecaja logističkih aktivnosti na ekološki sustav, pri čemu je naglasak na održivoj ekološkoj orijentaciji, tijesno povezanoj s održivim razvojem. Istraživanje opisano u radu odnosi se na aspekte zaštite okoliša u malim i srednjim poduzećima za šumarstvo i preradu drva u Slovačkoj u kontekstu održivog razvoja i zelene logistike. Kako bi se ostvario glavni cilj istraživanja, provedeno je iskustveno istraživanje radi određivanja razine razumijevanja i implementacije aktivnosti zelene logistike te mogućnosti njezine buduće implementacije. Istraživanje je pokazalo da 28,8 % poduzeća u svom dosadašnjem radu nije imalo nikakvih iskustava sa zelenom logistikom. Najveću prepreku uvođenju zelene logistike čine visoki troškovi implementacije, što je potvrdilo 62 % anketiranih poduzeća. Na osnovi rezultata istraživanja predložene su nove mogućnosti razvoja koncepta zelene logistike u slovačkim malim i srednjim pogonima u šumarstvu i drvoprerađivačkoj industriji kao dijela održivog razvoja poduzeća

Highly photoactive anatase foams prepared from lyophilized aqueouscolloids of peroxo-polytitanic acid

tPeroxo-polytitanic acid foams annealed at temperature above 500◦C lose volatile components and excessof oxygen providing anatase in the form of thin leaves consisting of intergrown nanocrystalline anataseparticles which transform at temperatures above 850◦C to rutile. The size and shape of the initialleaflets forming the foam is preserved up to ∼900◦C. We observed that the annealed material is highlyphotoactive, owing to highly anisotropic shape of anatase aggregates and their perfect crystallinity. Out-standing photocatalytic activity determined by measuring the kinetics of degradation of Methylene Blue(MB) and 4-chlorphenol (4-CP) as well as measuring the formation of hydroxyl radical spin adductsby EPR spectroscopy was observed. All three methods demonstrated significantly higher activity incomparison with the Degussa P25 photocatalyst. Both methods used for photoactivity tests providedsimilar results, the activity increased with increasing annealing temperature in order 500◦C < DegussaP25 < 600◦C < 850–950◦C. Results of measurement of formation of •OH radicals by EPR also confirmedthe unusually high activity of our materials. In comparison with the Degussa P25, the sample annealedat 950◦C showed significantly higher production of•OH radicals