Chemical vapor infiltration method for deposition of gold nanoparticles on porous alumina supports

Knudsen’s effusion method with mass spectral analysis of the composition of the gas phase was used to measure the temperature dependence of the saturated vapor of several (CH₃)₂AuL chelate complexes and to determine the thermodynamic parameters of their sublimation. Based on the results of this study, conditions for chemical vapor deposition of gold using dimethylgold(III) chelates were chosen. Gold nanoparticles were synthesized by chemical vapor deposition (infiltration) of (CH₃)₂Au(acac) on porous granules of γ-Al₂O₃ with subsequent calcination in air at 325°C. Particle size and the chemical state of gold in Au/γ-Al₂O₃ systems were evaluated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). A vapor infiltration procedure is suggested to prepare metallic gold particles ≤5 nm in diameter from Au/γ-Al₂O₃. It is shown that Au/γ-Al₂O₃ systems obtained by chemical vapor infiltration and containing small gold crystallites possess high catalytic activity in CO oxidation reactions at 40°C.     

Numerical Characteristics of a Random Variable Related to the Engel Expansions of Real Numbers

Ukrainian Mathematical Journal - It is known that any number x ∈ (0; 1] ≡ Ω has a unique Engel expansion $$ x=\sum \limits_{n=1}^{\infty}\frac{1}{\left({p}_1(x)+1\right)\dots...     

Structure and spectroscopy of NaNd(SP)<Subscript>4</Subscript> chelate: a new type of lanthanide luminophore

Lanthanide β-diketones and their derivatives are extensively studied coordination compounds, due to their luminescent properties and many possible applications. The tetrakisNd(III) complex with phosphorylated sulfonylamides derivatives of β-diketones was synthesized. The X-ray diffraction showed that the compound of formula {[Na[Ln(SP)₄]} _n (SP = C₆H₅S(O)2NP(O)(OCH₃)₂; Ln = Nd(III) crystallize in the monoclinic P2₁/c space group with the following unit-cell parameters: a = 22.006(4)A, b = 11.075(2)A, c = 22.334(5)A, and β = 118.71(3)°. The molecular structure of the investigated compound is polymeric. The lanthanide ions as well as the sodium ions are coordinated by sulfonyl and phosphoryl groups of the ligand, and because of the bridging behavior, link different units of the polymer. High-resolution absorption, emission, and excitation spectra of neodymium crystals were measured at 298, 77, and 4K temperatures. The sensitized emission of [Na[Nd(III)(L)₄]} _n chelate in the IR range of the spectrum was recorded. This kind of the compounds can be used in organic light emitting diodes in compact display technology. The spectral characteristic of the compound is controlled by donor–acceptor properties and electron-hole transporting chemical groups. Those factors affect the energy level location, energy transfer (ET), electron–phonon coupling, and finally the luminescence quantum yield. The optical behavior of the title compound was characterised by crystal field (CF), correlation crystal field (CCF), and electron transition probability calculations. X-ray structural data and the nephelauxetic effect check the role of the character of the bonding. The IR spectra were used to analyze the vibronic components in electronic transitions. The role of ligands, singlet and triplet states in energy transfer, are discussed. The ET mechanism and emission quenching pathways are proposed. Some spectroscopic parameters will be compared with earlier reported NaNdWo₄ × H₂O (Wo = CCl₃ CONPO(OCH₃)₂).     

Features of the real structure of pseudoboehmites: Violations of the structure and layer packing caused by crystallization water

Rietveld structure refinement and simulation of the diffraction patterns of partially disordered materials are used to study the real structure of nanoscale pseudoboehmite samples obtained by different technologies. The effect of various violations in the structure of these nanomaterials on diffraction patterns is analyzed. The introduction of corrections for the Lorentz and polarization factors in the determination of the cell parameter b by the position of the 020 diffraction peak in the pattern is shown to be important. A model for the atomic structure of pseudoboehmite is proposed. The model involves additional water molecules as compared to the structure of boehmite. The water molecules in the interlayer space of the layered boehmite structure are found to violate its regularity, which results in a decrease in the size of crystallites.     

Composition, structure, and properties of iron-rich nontronites of different origins

The composition, structure, and properties of smectites of different origins have been studied by X-ray diffraction, IR spectroscopy, scanning electron microscopy, and microprobe analysis. The results showed that nontronites of different origins differ in composition, properties, morphology, and IR spectroscopic characteristics. Depending on the degree of structural order and the negative charge of iron-silicate layers in nontronites, the shift of the 001 reflection to smaller angles as a result of impregnation with ethylene glycol (this shift is characteristic of the smectite group) occurs differently. The calculated values of the parameter b (from 9.11 to 9.14Å) are valid for the extreme terms of dioctahedral smectite representatives: nontronites.     

Structural features of finely dispersed pseudoboehmite obtained by a sol-gel method

Simulation of diffraction patterns, radial distribution function analysis, and electron microscopy are applied to study the features of the structure of nanosized pseudoboehmite obtained by the sol-gel method. It is found to consist of plate-like particles with a thickness of one lattice constant in the [010] direction. Such a structure of the pseudoboehmite particles results in the absence of the 020 diffraction peak in the diffraction pattern.     

NMR study of localization and mobility of 1‐phenylethanol enantiomers in homochiral metal‐organic sorbent Zn2(bdc)(S‐lac)(dmf)

Structural features of localization of chiral isomers of 1‐phenylethanol (R‐PhEtOH and S‐PhEtOH) and their mobility activation in homochiral metal‐organic [Zn₂(bdc)(S‐lac)(dmf)] sorbent were studied with ¹H and ¹³C NMR methods. ¹³C NMR chemical shifts do not show obvious advantage of selective interaction of molecule guests. But activation molecular mobility of S‐PhEtOH and R‐PhEtOH clearly indicates that stabilization of [Zn₂(bdc)(S‐lac)(dmf)]·S‐PhEtOH structure is more preferable than stabilization of [Zn₂(bdc)(S‐lac)(dmf)]·R‐PhEtOH structure. Copyright © 2015 John Wiley & Sons, Ltd.     

Scaled unscented transform Gaussian sum filter: Theory and application

In this work we consider the state estimation problem in nonlinear/non-Gaussian systems. We introduce a framework, called the scaled unscented transform Gaussian sum filter (SUT-GSF), which combines two ideas: the scaled unscented Kalman filter (SUKF) based on the concept of scaled unscented transform (SUT) (Julier and Uhlmann (2004) [16]), and the Gaussian mixture model (GMM). The SUT is used to approximate the mean and covariance of a Gaussian random variable which is transformed by a nonlinear function, while the GMM is adopted to approximate the probability density function (pdf) of a random variable through a set of Gaussian distributions. With these two tools, a framework can be set up to assimilate nonlinear systems in a recursive way. Within this framework, one can treat a nonlinear stochastic system as a mixture model of a set of sub-systems, each of which takes the form of a nonlinear system driven by a known Gaussian random process. Then, for each sub-system, one applies the SUKF to estimate the mean and covariance of the underlying Gaussian random variable transformed by the nonlinear governing equations of the sub-system. Incorporating the estimations of the sub-systems into the GMM gives an explicit (approximate) form of the pdf, which can be regarded as a “complete” solution to the state estimation problem, as all of the statistical information of interest can be obtained from the explicit form of the pdf (Arulampalam et al. (2002) [7]).In applications, a potential problem of a Gaussian sum filter is that the number of Gaussian distributions may increase very rapidly. To this end, we also propose an auxiliary algorithm to conduct pdf re-approximation so that the number of Gaussian distributions can be reduced. With the auxiliary algorithm, in principle the SUT-GSF can achieve almost the same computational speed as the SUKF if the SUT-GSF is implemented in parallel.As an example, we will use the SUT-GSF to assimilate a 40-dimensional system due to Lorenz and Emanuel (1998) [27]. We will present the details of implementing the SUT-GSF and examine the effects of filter parameters on the performance of the SUT-GSF.