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We explore into the role of the organic ligands composition surrounding Au nanoparticles (NPs) toward internanoparticles distance changes and film structure during vapor sensing by the use of in situgrazing-incidence small-angle X-ray scattering (GISAXS) and other relevant techniques. We observed distinct changes in core-to-coredistance and film structure upon measured concentrations of polar ethanol (EtOH) and nonpolar toluene (Tol) vapors. As-formed tetraoctylammonium bromide (TOABr)-coated Au NPs (SNPs) film exhibited ∼0.4 nm core-to-core increase in distance and improved SNPs correlation upon 80% Tol. In the presence of EtOH, SNPs distance seems not to change and correlation critically diminishes, leading to an amorphous film. As-formed films were exchanged with nonanedithiol (NDT) and exposed to 100% Tol vapor. Interestingly, the incorporation of NDT increased distance between NPs and rendered film flexibility. It is determine that just a small number of S, from NDT ligands, binds to Au NPs, and those exchanged alkanedithiol chains adopted a loop conformation around the Au NPs as evidenced by X-ray absorption near-edge structure (XANES) and kink defects by Fourier transformed infrared (FT-IR) experiments, respectively. These findings may solve some fundamental questions about internanoparticle distance-dependent phenomena such as electron transport in chemiresistors and coupling effects in localized surface plasmon resonance (LSPR) solid-state sensors.

A reactive hydride composite (RHC) with initial composition 3CaH2+ 4MgB2+ CaF2was studied by in situ synchrotron radiation powder X-ray diffraction (SR-PXD) and X-ray absorption near edge structure (XANES) at the B K-edge and at the Ca K-edge. The hydrogenation reaction proceeds by an unknown intermediate. No evidence of intermediates was observed during the dehydrogenation reaction. B and Ca K-edge XANES results hint to a closed interaction of CaF2and Ca(BH4)2. The main function of CaF2in the 3CaH2+ 4MgB2+ CaF2RHC is as a dopant for the hydrogenation and dehydrogenation reactions.

Gold nanoparticle-(AuNP)-modified carbon graphite surfaces have been prepared by simple immersion of highly oriented pyrolytic graphite (HOPG) in hexane solutions containing 3 nm diameter butanethiol- or nonanethiol-capped nanoparticles. The AuNP adsorb on the HOPG surface free of unbounded thiols, remaining unchanged with time. The amount of adsorbed thiol-protected AuNP depends on concentration and time. The reductive desorption of thiols from the AuNP produces an efficient release of more than 90% of the AuNP from the carbon surface to the aqueous solution. The remaining thiol-free Au nanoparticles do not sinter on the HOPG, forming stable and electrochemically active islands. These results could open interesting possibilities for easy transfer of thiol-capped metallic NP from one environment to another, for controlled release of biomolecules from metallic NP, and for the preparation of catalytic or decontamination systems on large area C surfaces.

Molybdena-containing ultrastable (HY) zeolites, prepared using several Mo precursors and activation procedures, were characterized by X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS). Combined XANES Mo L-edge and XPS results revealed that the Mo 4d electronic level is not strongly influenced by the preparation procedures but that it is clearly modified by the presence of Pd. The splitting of 2.4−2.6 eV obtained in the white line at both Mo LII,III-edges clearly indicated that Mo was tetrahedrally coordinated in all dehydrated catalysts. The Mo oxidation state, evaluated by the energy shift in the absorption edge, was also independent of the synthesis process. The Mo LII-edge is discussed for the first time as a very sensitive probe to determine the nature of Mo species. Even the XANES LIII-edge relative intensity of the maximum at the split white line depends on the Mo coordination; at the LII-edge, intensities do not depend on Mo coordination alone. This aspect should be associated, consistent with the binding energy (BE) of 3d levels observed by XPS, with the presence of Al atoms at the second Mo-surrounding in Mo-exchanged sites in zeolites.

The effect of reduction treatments in H2 at 500 °C in both wet and dry atmosphere on mono and bimetallic In−zeolite supported catalysts has been studied using the perturbed angular correlation technique. The relaxation in the observed hyperfine interaction has been associated with the formation of oxygen vacancies in the indium sesquioxide particles present on the external surface of the catalysts. The addition of Pt has consequences for the relaxation process. The effect of Pt atoms could be associated with the trapping of vacancies, thus slowing down their jump frequency. This particular and indirect In−Pt interaction does not seem to have any effect on the enhancement of the catalytic activity observed in the bimetallic sample. A new indium species with cubic symmetry for the In site, i.e., metallic indium and/or In2O3 nanosized crystallites, was detected in reduced In/ferrierite and InPt/ferrierite samples.

This paper presents a detailed discussion of the structure of tungsten phosphide and its relationship to simpler crystalline forms. The structure (space group Pbnm) is based on distorted hexagonal prisms with the phosphorus atoms forming P−P chains. Measurements by ³¹P magic angle spinning nuclear magnetic resonance show that there is only one type of phosphorus with a Knight shift of 255 ppm from 85% H3PO4, which is located in a highly anisotropic environment. Numerical simulations of extended X-ray absorption fine structure data at the W L3-edge give good agreement with crystallographic data. The W−P distance in WP was found to be 0.246 nm compared to the value of 0.247 nm obtained by X-ray diffraction. The catalytic activity of tungsten phosphide in the hydrotreating of a simulated petroleum feed is reported and compared to those of other tungsten compounds on an areal basis. Bulk (WP) and supported tungsten phosphide (WP/SiO2) are found to be more active in HDS and HDN than tungsten carbide (WC), tungsten nitride (W2N), tungsten sulfide (WS2), and more active in HDN than a commercial Ni−Mo−S/Al2O3 catalyst. The enhanced activity may be related to a considerably reduced white line area in the X-ray absorption edge of WP and WP/SiO2 compared to W metal, which makes their electronic structure resemble those of the highly active elements, Os and Ir, to the right in the periodic table.

K−ferrierite co-exchanged with Pt and In (PtIn(ferrierite)), with different pretreatments, is characterized by EXAFS (extended X-ray absorption fine structure), TDPAC (time differential perturbed angular correlation), TPR (temperature-programmed reduction), and hydrogen chemisorption. The presence of different In and Pt species is correlated with activity and selectivity during the NO selective reduction (SCR) with CH4 in the presence of excess oxygen. The reduction of PtIn(ferrierite) catalyst under controlled conditions (hydrogen at 350 or 500 °C) strongly promotes the activity of the said catalyst. The reduction at 350 °C results in the formation of small Pt° crystals, stable under wet reaction conditions, which probably favor both the oxidation of NO to NO2 and the adsorption of the said species, thus increasing the overall reaction rate. The reduction at 500 °C further increases the reaction rate because it promotes the formation of new (InO)⁺ active species from the reduction of In2O3 at the catalyst external surface. Small crystals of Pt° are also formed when the calcined catalyst is treated under wet reaction conditions, thus increasing the reaction rate to an extent similar to the one observed for the catalyst reduced at 350 °C.

Abstract: We report a new variation of the well-established experimental arteriovenous malformation (AVM) model in swine. To provide high flow through the rete mirabile (nidus, RM) and thereby to reduce the rate of spontaneous thrombosis of the AVM, we performed an end-to-end anastomosis of the left common carotid artery (CCA) and the external jugular vein (EJV) microsurgically in three micropigs. After 1 and 4 months the animals underwent angiograms of the CCA and vertebral artery (VA). In all cases the diversion of the blood through the RM was patent, up to the 4 months follow-up. We observed an arteriovenous fistula (arteriovenous pseudomalformation, pAVF) between the VA and the EJV in each case at both 1 and 4 months. This modification of the well-known AVM model in the micropig could be used to monitor long-term changes after embolisation, avoiding the naturally high rate of spontaneous thrombosis. This two-in-one model is thus well suited for preclinical testing of embolic materials.

Alumina-supported molybdenum phosphide (MoP/Al2O3) catalysts were prepared by temperature-programmed reduction of supported phosphate precursors in H2 at 0.083 K s^-1 to 1123 K. The catalysts had excellent activity in the simultaneous hydrodenitrogenation (HDN) of quinoline and hydrodesulfurization (HDS) of dibenzothiophene at realistic conditions [P = 3.1 MPa (450 psig) and T = 643 K (370 °C)]. The catalysts surpassed the performance of a sulfided commercial Ni−Mo−S/Al2O3 catalyst in both HDN and HDS. X-ray absorption fine structure (XAFS) analysis of the supported samples indicated the presence of dispersed species retaining metallic bonding with a characteristic Mo−P distance of 0.243 nm but showing considerable attenuation in Mo−Mo linkages.

The well-known porcine arteriovenous malformation (AVM) model introduced by Massoud et al has been widely used as an acute-phase model. However, there are no data available on the patency rate in long-term follow-up. Therefore this study is dedicated to the natural history of porcine AVM model after creation.Three piglets (Yucatan micropigs, aged 12 to 14 months) were used in this study. The model was created by microsurgical anastomosis in an end-to-end fashion between the common carotid artery (CCA) and external jugular vein (EJV) on the left side, and by direct ligation of the left external carotid artery (ECA). Angiography was performed before and immediately after model creation, as well as at 44, 103, 188 and 245 days in all animals.A successful high-flow brain AVM model was established in all animals. The fistula created by end-to-end anastomosis remained intact and thus the successful AVM model maintained in all models over a follow-up period as long as more than eight months.The AVM-model in swine could be used as a chronic model to test the neurointerventional techniques of AVM treatment. We re-created the well known AVM-model by a terminal anastomosis between CCA and EJV and we hypothesize that the good long-term patency of the model is related to the type of anastomosis performed between CCA and EJV.

Time Differential Perturbed Angular Correlation (TDPAC) experiments using 111In as probe were performed in order to determine the nature of In-sites in In-ferrierite (In/FER), before and after the incorporation of Pt through the hyperfine interaction between the nuclear quadrupole moment of the probe's nucleus and the extranuclear electric field gradient (EFG). Extended X-ray Absorption Fine Structure (EXAFS) measurements were performed to measure the absorbance above the Pt's LIIIabsorption edge in the transmission mode in order to determine the local environment of Pt atoms in Pt/FER and In Pt/FER catalysts. TDPAC spectra of 111In in In/FER and InPt/FER taken at 500°C in air indicated that there are no changes in the indium surroundings after the incorporation of Pt. Three sites were found for indium in both samples. Two of them correspond to the two sites of indium in ln2O3and the third one is attributed to In in exchange sites of the zeolites. Their population, quadrupole frequencies and asymmetry parameters didn't change with the incorporation of Pt. EXAFS experiments showed similar near neighborhood Pt-0 distances and Pt coordination number in Pt/FER and In Pt/FER samples. There is no evidence of the presence of any In-Pt bimetallic entity in In Pt/FER catalyst.

We present Perturbed Angular Correlation (PAC) results of the electric-nuclear quadrupole interaction at lxl Ta located at the nonequivalent cation sites of cubic C-Sm2O3and monoclinic B-Sm2O3 free of defects. The application of the empirical Cd/Ta correlation found in binary oxides allowed us to correlate the interactions with each site and to identify the single Sm site populated in 111In-implanted B-Sm2O3experiments. The preferential site occupation of Cd and Ta in B-Samaria is discussed in terms of the “chemistry” of the probe-atoms.

Silicalite-supportedindium catalysts (In/H-ZSM5) were characterized by time differential perturbed angular correlation (PAC) and temperature-programmed reduction (TPR). The presence of different indium species was correlated with activity and selectivity during the NO selective catalytic reduction (SCR) with CH4 in the presence of excess oxygen. The main species identified on the In/H-ZSM5 surface were In2O3 (indium sesquioxide crystals); In+Z− and (InO)+Z− (different indium species exchanged in the zeolitic matrix); and highly dispersed noncrystalline In oxide species not bonded to the zeolitic matrix. Catalysts that were impregnated and then calcined at 500°C had low activity for the reaction under study, showing the presence of only In2O3 and noncrystalline In oxide species. Treatment at 750°C in O2 or at 500°C in H2 followed by reoxidation at the same temperature resulted in active catalysts showing an appreciable concentration of (InO)+Z− active species. The same active species were formed after indium ion exchange of NH4-ZSM5 was followed by calcination at 500°C. The PAC technique proved to be a powerful tool for the identification and quantification of indium species present on the surface of an H-ZSM5 support.

Abstract: In connection with a general study of the evolution of tin-oxygen thin films, we report here on the hyperfine interactions of181Ta substitutionally replacting tin in the isolated phases SnO and SnO2. For this purpose, pure SnO pressed powder and a thin SnO2 film were implanted with181Hf. In both cases, unique quadrupole frequencies were found after thermal annealing treatments. The results indicate that the following hyperfine parameters: υ Q = 740.6(2.1) MHz, η=0.07(2) and υ Q = 971.5(1.9) MHz, η=0.72(1) characterize181Ta in SnO and SnO2, respectively.

The dispersion of metal oxides on supports is a problem currently being investigated in supported catalysts. On the other hand, a nuclear spectroscopy technique, namely time differential perturbed angular correlation (TDPAC), has been used in extensive investigations on Mo-based catalysts. This technique, through the measurement of the local electric field gradient (EFG) at radioactive probes sites, can give information about the characteristics (coordination, symmetry, distortions, etc.) of the different environments of the probes, their concentration and modifications related to in situ conditions (temperature, atmosphere, pressure, etc.) TDPAC technique was used in the present work to investigate the dispersion of molybdenum oxides on Al2O3, TiO2/Al2O3, and SiO2. The ⁹⁹Mo obtained by neutron irradiation of natural molybdenum present in the samples was used as TDPAC probe. Measurements at room temperature and higher ones as well as with different Mo concentrations in the samples were performed. The corresponding results allowed us through the fitted hyperfine parameters to find out the dispersion, type of adsorbed Mo−O species, and their relative abundances. For Mo concentrations below the theoretical monolayer we were able to find bulklike MoO3 and two-dimensional-like Mo oxides. Previous results obtained with TDPAC and calculations based on a point charge model suggest different MoO3 crystallites sites for each support. The structures of the monolayer type molybdena are probably different in each catalyst.

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