Kinetics of interaction of gas phase oxygen with cerium-gadolinium oxide

The method of isotopic exchange with gas phase analysis was used to study the kinetics of oxygen interaction with the Ce_0.80Gd_0.20O_{1.90 ? ??} oxide at the oxygen pressure of 0.27?C1.33 kPa in the temperature range of 700?C800°C. The values of oxygen interphase exchange rate and diffusion coefficient, and also effective activation energies of the processes of oxygen exchange and diffusion were determined. The contributions of three exchange types and amounts of equivalent exchangeable oxygen were calculated. It was shown that the limiting exchange stage is the process of dissociative oxygen adsorption/desorption on the surface of the Ce_0.80Gd_0.20O_{1.90 - ??} oxide.     

ANIONIC SYNTHESIS OF A “CLICKABLE” MIDDLE-CHAIN AZIDE-FUNCTIONALIZED POLYSTYRENE AND ITS APPLICATION IN SHAPE AMPHIPHILES

"Click chemistry" is, by definition, a general functionalization methodology (GFM) and its marriage with living anionic polymerization is particularly powerful in precise macromolecular synthesis. This paper reports the synthesis of a "clickable" middle-chain azide-functionalized polystyrene (mPS-N3 ) by anionic polymerization and its application in the preparation of novel shape amphiphiles based on polyhedral oligomeric silsesquioxane (POSS). The mPS-N3 was synthesized by coupling living poly(styryl)lithium chains (PSLi) with 3-chloropropylmethyldichlorosilane and subsequent nucleophilic substitution of the chloro group in the presence of sodium azide. Excess PSLi was end-capped with ethylene oxide to facilitate its removal by flash chromatography. The mPS-N3 was then derived into a giant lipid-like shape amphiphile in two steps following a sequential "click" strategy. The copper(I)-catalyzed azide-alkyne cycloaddition between mPS-N3 and alkyne-functionalized vinyl-substituted POSS derivative (VPOSS-alkyne) ensured quantitative ligation to give polystyrene with VPOSS tethered at the middle of the chain (mPS-VPOSS). The thiol-ene reaction with 1-thioglycerol transforms the vinyl groups on the POSS periphery to hydroxyls, resulting in an amphiphilic shape amphiphile, mPS-DPOSS. This synthetic approach is highly efficient and modular. It demonstrates the "click" philosophy of facile complex molecule construction from a library of simple building blocks and also suggests that mPS-N3 can be used as a versatile "clickable" motif in polymer science for the precise synthesis of complex macromolecules.     

An XPS and STM study of the size effect in NO adsorption on gold nanoparticles

The effect of the gold particle size, temperature of the model gold catalyst, and NO pressure on the composition of the adsorption layer was studied by in situ XPS and STM methods. Adsorption of nitric oxide was carried out on gold nanoparticles with a mean size of 2?C7 nm prepared on the thin film surface of alumina. In high-vacuum conditions (P _NO ?? 10^?5 Pa), only atomically adsorbed nitrogen is formed on the surface of gold nanoparticles. At about 1 Pa pressure of NO and in the temperature range from 325 to 475 K, atomically adsorbed nitrogen coexists with the N₂O adsorption complex. The surface concentration of the adsorbed species changes with a change in both the mean gold particle size and adsorption temperature. The saturation coverage of the surface with the nitrogen-containing complexes is observed for the sample with a mean size of gold particles of 4 nm. The surface of these samples is mainly covered with atomically adsorbed nitrogen, the saturation coverage of adsorbed nitrogen of about ??0.6 monolayer is attained at T = 473 K. The change in the composition of the adsorption layer with temperature of the catalysts agrees with the literature data on the corresponding temperature dependence of the selectivity of N₂ formation observed in the catalytic reduction of NO with carbon monoxide on the Au/Al₂O₃ catalyst. The dependences of the composition of the adsorption layer on the mean size of Au nanoparticles (size effect) and temperature of the catalyst are explained by the sensitivity of NO adsorption to specific features of the gold surface.     

Accumulation of uranium, transuranium and fission products on stainless steel surfaces II. Sorption studies in a laboratory model system

Within the frame of a joint project, the accumulation of the uranium and transuranium (TRU) species on some structural materials used at Soviet made VVER-type pressurized water reactors (such as heat exchanger tube of steam generators and stainless steel canister material) has been studied. The experiments were carried out in a laboratory model system. During the sorption studies, boric acid coolants provided by the Paks Nuclear Power Plant (Paks NPP) were circulated for a period of 30 h. Solution and tube samples obtained in the course of above experiments were analyzed by independent methods (??- and ??-spectrometry, ICP-MS, SEM-EDX, voltammetry and XPS). The experimental results reveal that: (i) the surface excess of the TRU nuclides studied is extremely low (less than 1% of a monolayer coverage); (ii) the surface excess of uranium species measured on the SG tube surfaces is significantly higher, after 30 h sorption period (??_sample = 1.0 ??g cm^?2 U ? 3.7 × 10^?9 mol cm^?2 UO₂) exceeds a monolayer coverage; (iii) the mechanistic features of the contamination processes (specific or non-specific adsorption, deposition of colloidal and/or disperse particles) depend decisively upon the nature of the studied radionuclides and the chemical structure and composition of the oxide layer formed on stainless steel surfaces.     

Synthesis and characterization of ultrafine spinel ferrite obtained by precursor combustion technique

Nanoparticles of the spinel ferrite, Co_0.6Ni_0.4Fe₂O₄ have been synthesized by the precursor combustion technique. This synthetic route makes use of a novel precursor viz. metal fumarato hydrazinate which decomposes autocatalytically after ignition to yield nanosized spinel ferrite. The X-ray powder diffraction of the ??as prepared?? oxide confirms the formation of monophasic nanocrystalline cobalt nickel ferrite. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric and differential thermal analysis. The precursor has also been characterized by FTIR, and chemical analysis and its chemical composition has been fixed as Co_0.6Ni_0.4Fe₂(C₄H₂O₄)₃·6N₂H₄. The Curie temperature of the ??as prepared?? oxide was determined by ac susceptibility measurements.     

Density functional theory study on quasi-three-dimensional oxidized platinum surface: phase transition between ��-PtO2-like and ��-PtO2-like structures

We investigate the oxidation process of a platinum surface by using the density functional theory approach under the periodic boundary condition. This oxidation process has received much attention because it is an initial step in the dissolution of platinum catalysts in polymer electrolyte fuel cells. In this research, we determine the optimized structure of ?? -PtO₂-like and ??-PtO₂-like oxidized platinum surfaces, which have recently been proposed on the basis of in situ X-ray diffraction analysis, at the Kohn Sham density functional theory (KS-DFT) generalized gradient approximation (GGA) level of theory. We discuss the phase transition from the ??-PtO₂-like surface to the ??-PtO₂-like surface, including the place-exchange reaction between oxygen and platinum atoms. We propose an intermediate structure in the phase transition, and show that the ??-PtO₂-like structure can be formed directly from this intermediate structure.     

Oxygen dissolution in polycrystalline palladium at O2 pressures of 0.1 to 100 Pa

Oxygen dissolution in polycrystalline palladium Pd(poly) at O₂ pressures ( $P_{O_2 } $ ) of 0.1 to 100 Pa and a temperature of 600 K has been investigated by temperature-programmed desorption. The dissolution process under these conditions includes O₂ chemisorption on the oxide film surface, the insertion of Oads atoms under the oxide layer, and their diffusion into the subsurface layers of palladium. During chemisorption, a structure ensuring that the O_ads coverage of the surface increases with increasing $P_{O_2 } $ forms on the surface of the oxide film. This is favorable for O_ads penetration through the oxide film and increases the amount of absorbed oxygen. The O_ads coverage of the surface calculated via the Langmuir equation at an O₂ desorption activation energy of E _des = 125 kJ/mol correlates with the number of absorbed oxygen monolayers (n). At n ≥ 1, oxygen absorption by Pd(poly) is due to the diffusion of O atoms in the palladium lattice. After the accumulation of 14–18 oxygen monolayers in the subsurface layers of palladium, oxygen absorption practically stops depending on $P_{O_2 } $ . Thus, the acceleration of oxygen dissolution in palladium is due to the formation of the surface oxide film and the increase in the O_ads coverage of this film, which facilitates the insertion of O_ads atoms into the subsurface layers of palladium.     

Hydrophilic nature and sorption-diffusion properties of nanocomposite hybrid polysulfone films

Hybrid nanocomposite films containing silica (??11.4 wt.%) or titania (??18.8 wt.%) in the polymer matrix were prepared by the sol-gel method using the hydrolytic polycondensation of tetraethoxysilane and tetrabutoxysilane in a THF solution of aromatic polymer, polysulfone (PSF). The influence of the oxide nature and the film composition on the structure, the interaction of the polymer with oxides, hydrophilicity, and sorption-diffusion properties of the hybrid films were studied by FTIR spectroscopy, atomic force microscopy, dynamic light scattering, and a complex of other physicochemical methods. The absence of chemical or intermolecular hydrogen bonds between the polymer and oxide particles in the PSF films was shown. The average size of the oxides (SiO₂, ??20 nm; TiO₂, ??90 nm) in the films and roughness of their surface (??0.2?C0.8 nm) were determined. The introduction of oxides into the polymer matrix increases the hydrophilic properties and the ability of the PSF films to swell in water; the diffusion coefficients of water and permeability of water vapor in the PSF films also increase. Titania also induces a more considerable change in the structure of the polymer matrix and more strongly affects the sorption-diffusion properties of the hybrid films in aqueous solutions of THF. All prepared nanocomposite films PSF/SiO₂ and PSF/TiO₂ are capable of extracting an organic component from aqueous solutions and can be used as sorbents and membrane films for the removal of organic substances from the aqueous medium.     

Investigation of thermal behaviour of hybrid nanostructures based on Fe2O3 and PAMAM dendrimers

Dendrimers or biofunctionalized dendrimers can be assembled onto magnetic iron oxide nanoparticles to stabilize or functionalize inorganic nanoparticles. Carboxylated poly(amidoamine) PAMAM dendrimers (generation 4.5) have been used for the synthesis of iron oxide nanoparticles, resulting nanocomposites with potential biomedical applications. The present paper aims to systematically investigate the thermal behaviour of nanostructured hybrids based on ferric oxide and PAMAM dendrimers, by differential scanning calorimetry (DSC) technique. The novelty consists both in synthesis procedure of hybrid nanostructures as well as in DSC approach of these nanocomposites. For the first time, we propose a new method to prepare Fe₂O₃??dendrimer nanocomposite, using soft chemical process at high pressure. Commercial PAMAM dendrimers with carboxylic groups on its surface were used. When high pressure is applied, polymeric structures suffer morphological changes leading to hybrid nanostructures' formation. In the same time, crystallinity of inorganic nanoparticles is provided. DSC results showed an increase in thermal stability of composites as compared to commercial dendrimers. This could be due to the formation of strong interactions between ferric oxide and carboxyl groups, as confirmed by Fourier transform infrared spectroscopy. Electron microscopy analysis (SEM/EDX) and size measurements were performed to demonstrate the existence of nanosized particles.     

Prostate Cell Membrane Chromatography�CLC/MS Method for Screening ��1A-Adrenoceptor Antagonists from Lotus Plumule

The ??_1A-adrenoceptor (??_1A-AR) plays an important role in drug discovery and development. An online analytical method coupling prostate cell membrane chromatography (CMC) with high-performance liquid chromatography/mass spectrometry (LC/MS) was established to screen ??_1A-AR antagonists in traditional Chinese medicines (TCMs). The prostate cell membrane stationary phase (CMSP) was prepared by immobilizing the prostate cell membrane onto the surface of the silica carrier. The surface and chromatographic characteristics of the prostate CMSP were studied using tamsulosin as a model molecule. The retained fractions from the prostate CMC were analyzed by transferring them to an LC/MS system through a 10-port switch valve. The active component, which could act on the prostate cell membrane and receptor on it (such as ??_1A-AR), was determined using a displacement experiment. The results indicated that liensinine, isoliensine, and neferine from Lotus Plumule exhibited similar retention characteristics to the control drug tamsulosin when utilizing the prostate CMC model. This new prostate CMC?CLC/MS method is applicable for screening ??_1A-AR antagonists from TCMs such as Lotus Plumule and could be employed as a drug discovery tool for natural medicinal herbs.     

Theoretical DFT study of the structure and chemical activity of small indium(III) oxide clusters

The B3LYP/Lanl2dz and B3LYP/SDD levels of DFT have been used to describe the structural properties of small stoichiometric indium(III) oxide clusters. It was shown that the most stable structures for the monomer and dimer are linear and cubic, respectively, in origin. The most stable trimer is due to the formation of three eight-membered and two six-membered rings with alternation of In and O atoms. Among neutral and monocation tetrameric structures, formation of an ??arrowhead?? isomer is energetically less favorable than the global minimum structure that has eight six-membered and six four-membered rings. In the pentamer and octamer, a few centers of higher coordination number and a variety of In?CO bond lengths are observed. The other centers cannot be fitted to the characteristic bixbyite structure, however, so the larger octamer cannot be a good model for mimicking the properties of the In₂O₃ crystal structure. An H-terminated cluster model consisting of In₁₃O₂₇H₁₅ is proposed that well describes basic features of indium oxide and tin-doped indium oxide (ITO) structures.     

Distribution of zirconia nanoparticles in the matrix of poly(4,4′-oxydiphenylenepyromellitimide)

Poly(4,4??-oxydiphenylenepyromellitimide) is used as a polymer matrix for incorporation of zirconia nanoparticles with different compositions (ZrO₂ and Y_0.03Zr_0.97O_1.985), sizes (20 ± 5 and 10 ± 2 nm), and morphologies (spheres, hollow spheres, rods). The nanoparticles are incorporated during the synthesis of poly(amido acid), a prepolymer of polyimide, and ZrO₂ nanoparticles are pretreated with organosilicon compounds (tetraethoxysilane, ??-aminopropyltriethoxysilane, and 3-(trimethoxysilyl)propyl methacrylate). The effect of surface modification of ZrO₂ nanoparticles on their distribution in poly(4,4??-oxydiphenylenepyromellitimide), depending on the type of the organosilicon compound as well as on the dispersity, shape, and chemical composition of particles, is studied.     

Wettability conversion on the liquid flame spray generated superhydrophobic TiO2 nanoparticle coating on paper and board by photocatalytic decomposition of spontaneously accumulated carbonaceous overlayer

Titanium dioxide (TiO₂) is a photoactive material with various interesting and useful properties. One of those is the perfect wettability of TiO₂ surface after ultraviolet (UV) illumination. Wettability of a solid surface plays an important role in the field of printing, coating, and adhesion among others. Here we report on a superhydrophobic and photoactive liquid flame spray (LFS) generated TiO₂ nanoparticle coating that can be applied on web-like materials such as paper and board in one-step roll-to-roll process. The LFS TiO₂ nanoparticle coated paper and board were superhydrophobic instantly after the coating procedure because of spontaneously accumulated carbonaceous overlayer on TiO₂, and thus there was no need for any type of separate hydrophobization treatment. The highly photoactive LFS TiO₂ nanoparticle coating could be converted steplessly from superhydrophobic to superhydrophilic by UV-illumination, and the coating gave strong response to natural daylight illumination even in the shade. The superhydrophobic LFS TiO₂ coated surface can be used as an intelligent substrate, where photo-generated hydrophilic patterns guide the fluid setting and figure formation. Our study reveals that the wettability changes on the LFS TiO₂ surface were primarily caused by the photocatalytic removal of the carbonaceous material from TiO₂ during the UV-illumination and spontaneous accumulation of the carbonaceous material on the surface of the metal oxide during storage in the dark. The latter mechanism was found to be a temperature activated process which could be significantly speeded up by heat treatment. If other mechanisms such as surface oxidization, increment of hydroxyl groups, or charge separation played a role in the wetting phenomena on TiO₂, their effect was rather secondary as the removal and accumulation of the carbonaceous material dominated the wettability changes on the surface. Our study gives valuable information on the complex issue of photo-induced wettability changes on TiO₂.     

Calixarenes grafted with Bu2P(O)CH2O binding groups at the narrow rim: synthesis, structure and extraction of heterometallic Ru/Zn complexes

Calix[n]arenes (n?=?4, 6) existing in the cone, 1,3-alternate or 1,3,5-alternate conformations and functionalized by two, four or six Bu₂P(O)CH₂O groups have been synthesized by the alkylation of hydroxycalix[4,6]arenes with tosylate of dibutylhydroxymethylphosphine oxide. Their molecular and crystal structures as well as binding properties towards of heterometallic Ru/Zn complexes were investigated. Due to the ??calixarene effect?? the phosphine oxides are effective extractants for the Ru/Zn complexes.     

Reversibility of electrosurface transfer through eutectic interfaces of MeWO4|WO3 (Me ? Ca, Sr, Ba)

It is found that electrosurface transition (EST) through eutectic interfaces of (?/+)WO₃|MeWO₄(+/?) induced by electric field is a reversible process. In the case of the (?/+) polarity, nominally, in the ??direct experiment??, macro amounts of WO₃ from a W ₃ ^(?) brick are drawn in the (+) direction onto the inner surface of MeWO₄ forming a two-phase {ie1070-1} composite. Simultaneously, nonequivalent countertransport of Me ²⁺ within the W ₃ ^(?) brick occurs, which changes the color of W ₃ ^(?) from the natural hue to dark-green. Intercalation of Me ²⁺ into W ₃ ^(?) is proved by several spectroscopic methods. The key role in the EST phenomenon belongs to a nonautonomous electrolytic phase of MeW-s formed on the contact interface with WO₃|MeWO₄. The composition of MeW-s is close to W/Me ?? 2. As a result of EST, the cell acquires a more complicated structure: {fx1070-1} where |///| are interface regions occupied by the MeW-s phase. At the cathodic boundary of subcell {fx1070-2} the following process occurs: {fx1070-3}, The process at the anodic boundary is: {fx1070-4}. Ultimately, WO₃ is transported in the (+) direction (into the composite) and Me ²⁺ penetrates under the effect of the gradient in chemical potential into W ₃ ^(?) forming a dark-green Me _x WO₃ phase with its front reaching the (?) Pt electrode. After the end of the ??direct experiment??, the cell polarity was changed to (+/?) and the ??reverse experiment?? was carried out. Now, on the cathodic boundary | ₄ of subcell {fx1070-5} anions (WO₄)^2? are generated that are discharged on boundary ₃ | to oxide WO₃ that is intercalated into the right boundary of MeWO_{4 ? (3)}, where the rightmost composite region {ie1070-2} is formed. Thus, the mass of W ₃ ^(?) decreases; it becomes dark-green (see above) and the mass of the MeWO₄ disk continues growing and now its structure is as follows {ie1070-3}. It is important that the left W ₃ ⁽⁺⁾ disk that was dark-green after the ??direct experiment?? gradually becomes lighter in the ??reverse experiment?? up to its natural pale green color, i.e., Me ²⁺ is deintercalated from it: Me ²⁺: Me _x WO₃ + 1/2O₂ ?? xMe ²⁺ + 2e + WO₃. It is found that dependences of variations of disk masses ??m(Q) practically coincide for the ??direct?? and ??reverse?? experiments.     

Phase equilibria in the Tl2Te-PbTe-Bi2Te3 system

Phase equilibria in the Tl₂Te-PbTe-Bi₂Te₃ system were studied by differential thermal analysis, X-ray powder diffraction, and microhardness measurements. Some polythermal sections and isothermal (at 600 and 800 K) sections of the phase diagram and a projection of the liquidus surface were constructed. It was shown that the system is characterized by the formation of solid solutions with the Tl₅Te₃ structure (??) and solid solutions based on PbTe (??₁), Tl₂Te (??), Bi₂Te₃ (??), and two TlBiTe₂ (??₂ and ?á?₂) phases. Their homogeneity regions were determined. The liquidus surface consists of the primary crystallization fields of the ??-, ??₁-, ?á?₂-, and ??-phases and the compounds PbBi₂Te₄ and PbBi₄Te₇. The liquidus of the ?? phase is degenerate. The primary crystallization fields of the phases were determined, and the types and coordinates of in- and monovariant equilibria were found.     

Isotope effect of proton and deuteron adsorption site on zeolite-templated carbon using path integral molecular dynamics

To analyze the proton/deuteron (H/D) isotope effect on the stable adsorption sites on zeolite-templated carbon (ZTC), we have performed path integral molecular dynamics simulations including thermal and nuclear quantum effects with the semi-empirical PM3 potential at 300?K. Here, for the adsorption sites of additional proton (H*) and deuteron (D*), we chose different five carbon atoms labeled as ??-, ??₁-, ??₂-, ??-, and ??-carbons from edge to bottom for inside of buckybowl (C₃₆H₁₂ and C₃₆D₁₂). The stable adsorption sites of D* are observed on all carbon atoms, while those of H* are not observed on ??-carbon atom, but only on ??-, ??₁-, ??₂-, and ??-carbon atoms. This result is explained by the fact that H* can easily go over the barrier height for hydrogen transferring from ??- to ??₂-carbons at 300?K, since the zero-point energy of H* is greater than that of D*.     

Synthesis and thermal studies of the cobalt zinc ferrous fumarato-hydrazinate

Nanosize Co_1?x Zn _x Fe₂O₄ (x?=?0, 0.1, 0.3, and 0.4) have been synthesized by the precursor combustion technique via autocatalytic combustion of the mixed-metal fumarato-hydrazinate precursors. A key feature of these precursors is that they decompose autocatalytically once ignited to give the monophasic nanocrystalline ferrite. This fact is confirmed by X-ray powder diffraction analysis. The thermal decomposition pattern of the precursors has been studied by thermogravimetric and differential thermal analysis. The precursors have also been characterized by FTIR and chemical analysis to fix the chemical composition. The Curie temperature (T _c) of the ??as-prepared?? oxide was determined by alternating current susceptibility measurements.     

Simultaneous determination of levodopa and carbidopa by a novel nanostructure modified carbon paste electrode

The electrochemical behavior of levodopa (LD) was investigated on the surface of a carbon paste electrode modified with TiO₂ nanoparticles and 2,2??-(1,2 butanediylbis(nitriloethylidyne))-bis-hydroquinone (BNH). The prepared modified electrode showed an efficient catalytic role in the electrochemical oxidation of LD, leading to a remarkable decrease in oxidation overpotential and enhancement of the kinetics of the electrode reaction. The mechanism of the electrocatalytic process on the surface of the modified electrode was analyzed by obtaining the cyclic voltammograms in various potential sweep rates. This modified electrode exhibited well-separated oxidation peaks for LD and carbidopa (CD). The differential pulse voltammetry was applied as a very sensitive analytical method for the determination of LD and CD. A linear dynamic range of 2.0?C600.0 and 20.0?C400.0???M with a detection limit of 0.2???M (with sensitivity of 0.199 ??A ??M^?1) and 10???M (with sensitivity of 0.024???A???M^?1) was obtained for LD and CD, respectively. The modified electrode was prepared quite easily and renewed on the surface by simple polishing.