Phosphorus Nitride P3N5

Pure, stoichiometric, hydrogen-free, and crystalline phosphorus nitride P3N5 has been obtained for the first time by reaction of (PNCl2)3 and NH4Cl between 770 and 1050 K. The compound has been characterized by elemental analyses, 31P and 15N MAS NMR, EXAFS, IR spectroscopy, X-ray powder diffraction, and electron microscopy. In the solid a three-dimensional cross-linked network structure of corner sharing PN4 tetrahedra has been identified with 2/5 of the nitrogen atoms bonded to three P atoms and 3/5 of the nitrogen atoms bonded to two P atoms. By electron diffraction (ED) and high-resolution transmission electron microscopy (HRTEM) two distinguishable modifications α-P3N5 and β-P3N5 have been identified which differentiate only by the stacking order of identical sheets similar to the polytypes of SiC

Cinchonidine-Induced Restructuring of Pt/Al2O3 During Enantioselective Hydrogenation

The intrinsic selectivity of cinchonidine-modified Pt/alumina is poor in the hydrogenation of 3,5-di-(trifluoromethyl)-acetophenone but stirring of the catalyst system in toluene under nitrogen prior to reaction more than triples the ee. SEM and TEM analysis revealed dramatic restructuring of the catalyst and the Pt particles. We propose that the interaction of the hydroxy methyl-quinoline fragment ("anchoring moiety”) of cinchonidine with Pt is responsible for the restructuring. Reductive pretreatment at elevated temperature as well as the attrition induced by stirring in toluene accelerate the process. The higher ee is attributed to morphological changes of Pt, leading to the development of a more "selective” surface. The chirality of cinchonidine is unimportant in the restructuring and no correlation between the size of Pt particles and the ee has been foun

Visibly transparent & radiopaque inorganic organic composites from flame-made mixed-oxide fillers

Radiopaque composites have been produced from flame-made ytterbium/silica mixed oxide within a crosslinked methacrylate resin matrix. The refractive index of the filler powder increased with ytterbium oxide loading. A high transparency was achieved for a matching refractive index of the filler powder and the polymer in comparison to commercial materials with 52wt% ceramic filling. It was demonstrated that powder homogeneity with regard to particle morphology and distribution of the individual metal atoms is essential to obtain a highly transparent composite. In contrast, segregation of crystalline single-oxide phases drastically decreased the composite transparency despite similar specific surface areas, refractive indices and overall composition. The superior physical strength, transparency and radiopacity compared to composites made from conventional silica based-fillers makes the flame-made mixed-oxide fillers especially attractive for dental restoration material

Cinchonidine-Induced Restructuring of Pt/Al2O3 During Enantioselective Hydrogenation

ISSN:1011-372XISSN:1572-879

Material ejection and redeposition following atmospheric pressure near-field laser ablation on molecular solids

Near-field laser ablation (NF-LA) coupled with mass spectrometry (MS) is very promising for highly spatially resolved chemical analyses on various substrates at atmospheric pressure, for example, in materials and life science applications. Although nanoscale sample craters can be produced routinely, no molecular mass spectra of ablated material from craters of ≤1 µm diameter have ever been acquired by NF-LA MS at atmospheric pressure. Some of the pressing questions are thus how much of the ablated material is transported into the mass spectrometer and in what form. Therefore, material redeposition on the near-field tip's surface from laser ablation of molecular solids was characterized with scanning electron microscopy. The crater profiles were studied by scanning probe microscopy. The results shown in this study demonstrate that there could be as much as 70% of the ablated material deposited on the near-field tip's surface. The redeposited products were found to be confined to a height of ~50µm, thus suggesting that most components inside near-field ablation plumes propagate about the same distance for both anthracene and tris(8-hydroxyquinolinato)aluminum. Nanoparticles ablated from craters of ≤1 µm diameter are clearly observed. Furthermore, observation of tips after ablation of an anthracene surface angled at 60° with respect to a horizontal surface shows that the direction of the near-field ablation plume is neither in the direction of the surface normal nor towards the axis of incident laser beam but deflected further away from surface normal. Figure Material redeposition on the near-field tip's surface from laser ablation of molecular solids was characterized with scanning electron microscop

Feasibility of Methyl Mercaptane as Probe Molecule for Supported Gold Nanoparticle Surface Area Determination

Gold nanoparticles supported on TiO2 were probed by adsorption of methyl mercaptane (MM), and the process was quantified gravimetrically. This method allowed discrimination between weakly adsorbed (physisorbed) and strongly bound (chemisorbed) methyl mercaptane. Strong adsorption of MM occured on exposed Au faces, while low-temperature pre-treatment (30 °C) completely suppressed adsorption of MM on the TiO2 support. The thus obtained high selectivity of MM adsorption on Au enabled characterization of the gold surface area and the resulting values are comparable with other noble metal systems of similar average particle size. The estimated adsorption stoichiometry indicates that the entire Au surface is probed

Gold-Catalyzed Aerobic Oxidation of Benzyl Alcohol: Effect of Gold Particle Size on Activity and Selectivity in Different Solvents

The effect of the size of gold particles deposited on CeO2 and TiO2 supports on their catalytic behavior in the aerobic oxidation of benzyl alcohol in different solvents (mesitylene, toluene, and supercritical carbon dioxide) has been investigated. The size of supported gold particles deposited via a colloidal route was in the range 1.3-11.3nm, as determined by means of EXAFS and HAADF-STEM measurements. The catalytic performance of the supported gold catalysts in the different solvents revealed a significant effect of the gold particle size. Optimal activity was observed for catalysts with medium particle size (ca. 6.9nm) whereas smaller and bigger particles showed inferior activity. Identical trends for the activity-particle size relationship were found using Au/CeO2 and Au/TiO2 for the reaction at atmospheric pressure in conventional solvents (mesitylene, toluene) as well as under supercritical conditions (scCO2). Selectivity to benzaldehyde was only weakly affected by the gold particle size and mainly depended on reaction conditions. In supercritical CO2 (scCO2) selectivity was higher than in the conventional solvents under atmospheric pressure. All catalysts tested with particle sizes ranging from 1.3 to 11.3nm showed excellent selectivity of 99% or higher under supercritical condition

Multimineral nutritional supplements in a nano-CaO matrix

The fast dissolution of certain calcium-containing compounds makes them attractive carriers for trace minerals in nutritional applications, e.g., iron and zinc to alleviate mineral deficiencies in affected people. Here, CaO-based nanostructured mixed oxides containing nutritionally relevant amounts of Fe, Zn, Cu, and Mn were produced by one-step flame spray pyrolysis. The compounds were characterized by nitrogen adsorption, x-ray diffraction, (scanning) transmission electron microscopy, and thermogravimetric analysis. Dissolution in dilute acid (i.d.a.) was measured as an indicator of their in vivo bioavailability. High contents of calcium resulted in matrix encapsulation of iron and zinc preventing formation of poorly soluble oxides. For 3.6 ≤ Ca:Fe ≤ 10.8, Ca2Fe2O5 coexisted with CaO. For Ca/Zn compounds, no mixed oxides were obtained, indicating that the Ca/Zn composition can be tuned without affecting their solubility i.d.a. Aging under ambient conditions up to 225 days transformed CaO to CaCO3 without affecting iron solubility i.d.a. Furthermore, Cu and Mn could be readily incorporated in the nanostructured CaO matrix. All such compounds dissolved rapidly and completely i.d.a., suggesting good in vivo bioavailabilit

Scalable photonic sources using two-dimensional lead halide perovskite superlattices

Miniaturized photonic sources based on semiconducting two-dimensional (2D) materials offer new technological opportunities beyond the modern III-V platforms. For example, the quantum-confined 2D electronic structure aligns the exciton transition dipole moment parallel to the surface plane, thereby outcoupling more light to air which gives rise to high-efficiency quantum optics and electroluminescent devices. It requires scalable materials and processes to create the decoupled multi-quantum-well superlattices, in which individual 2D material layers are isolated by atomically thin quantum barriers. Here, we report decoupled multi-quantum-well superlattices comprised of the colloidal quantum wells of lead halide perovskites, with unprecedentedly ultrathin quantum barriers that screen interlayer interactions within the range of 6.5 Å. Crystallographic and 2D k-space spectroscopic analysis reveals that the transition dipole moment orientation of bright excitons in the superlattices is predominantly in-plane and independent of stacking layer and quantum barrier thickness, confirming interlayer decoupling

Operando Laboratory-Based Multi-Edge X-Ray Absorption Near-Edge Spectroscopy of Solid Catalysts

Laboratory-based X-ray absorption spectroscopy (XAS) and especially X-ray absorption near-edge structure (XANES) offers new opportunities in catalyst characterization and presents not only an alternative, but also a complementary approach to precious beamtime at synchrotron facilities. We successfully designed a laboratory-based setup for performing operando , quasi-simultaneous XANES analysis at multiple K edges, more specifically, operando XANES of mono-, bi-, and trimetallic CO 2 hydrogenation catalysts containing Ni, Fe, and Cu. Detailed operando XANES studies of the multi-element solid catalysts revealed metal-dependent differences in the reducibility and re-oxidation behavior and their influence on the catalytic performance in CO 2 hydrogenation. The applicability of operando laboratory-based XANES at multiple K edges paves the way for advanced multi-element catalyst characterization complementing detailed studies at synchrotron facilities.Peer reviewe