Influence of annealing on the structure of nanoporous oxide films on the surface of titanium‒aluminum powder alloy

Oxide films obtained during anodization of Ti?40% Al sintered powder samples in fluorine-containing electrolytes are investigated. With scanning electron microscopy and X-ray phase analysis, it is demonstrated that an X-ray amorphous nanoporous anodic oxide film is formed on the surface of the powder microparticles under optimal anodization conditions. After annealing at T = 1093 K in air and vacuum (10^?2 Pa), the oxide films are revealed to crystallize with its regular porous structure retained. The composition of the polycrystalline anodic-oxide films annealed in air is a mixture involving TiO₂ (anatase and rutile) and α- and γ-Al₂O₃ phases and Ti₂O₃ and Al₂TiO₅ traces. The vacuum annealing process makes it possible to identify TiO₂, in which anatase is the main phase, α- and γ-Al₂O₃, and Ti₂O₃ and TiO traces. However, rutile is not revealed. The presented results indicate that the application of the anodic nanostructuring of Ti?40% Al powders is promising for the obtainment of new photocatalytic active nanomaterials.     

Identification of transformation products from β‐blocking agents formed in wetland microcosms using LC‐Q‐ToF

Identification of degradation products from trace organic compounds, which may retain the biological activity of the parent compound, is an important step in understanding the long‐term effects of these compounds on the environment. Constructed wetlands have been successfully utilized to remove contaminants from wastewater effluent, including pharmacologically active compounds. However, relatively little is known about the transformation products formed during wetland treatment. In this study, three different wetland microcosm treatments were used to determine the biotransformation products of the β‐adrenoreceptor antagonists atenolol, metoprolol and propranolol. LC/ESI‐Q‐ToF run in the MS^E and MS/MS modes was used to identify and characterize the degradation products through the accurate masses of precursor and product ions. The results were compared with those of a reference standard when available. Several compounds not previously described as biotransformation products produced in wetlands were identified, including propranolol‐O‐sulfate, 1‐naphthol and the human metabolite N‐deaminated metoprolol. Transformation pathways were significantly affected by microcosm conditions and differed between compounds, despite the compounds' structural similarities. Altogether, a diverse range of transformation products in wetland microcosms were identified and elucidated using high resolving MS. This work shows that transformation products are not always easily predicted, nor formed via the same pathways even for structurally similar compounds. Copyright © 2016 John Wiley & Sons, Ltd.     

Geometric and electronic structure of methane adsorbed on a Pt surface

The electronic structure of methane adsorbed on Pt(977) is investigated using angle-resolved x-ray absorption spectroscopy (XAS) in combination with density functional theory spectrum calculations. XAS, which probes the unoccupied states atom specifically, shows the appearance of the symmetry-forbidden gas-phase lowest unoccupied molecular orbital due to s-p rehybridization. In addition new adsorption-induced states appear just above the Fermi level. A systematic investigation, where computed XA spectra are compared with the experiment, indicates elongation of the C-H bond pointing toward the surface to 1.18+/-0.05 A. The bond elongation arises due to mixing between bonding and antibonding C-H orbitals. Computed charge density difference plots show that no covalent chemical bond is formed between the adsorbate and substrate upon adsorption. The changes in electronic structure arise in order to minimize the Pauli repulsion by polarizing charge away from the surface toward the carbon atom of the methane molecule.     

Chemical stability of reversed phase high performance liquid chromatography silica under sodium hydroxide regeneration conditions

Chromatographic sorbents used within the purification of peptide or protein based active pharmaceutical ingredients (APIs) are commonly subjected to caustic regeneration procedures, so-called CIP treatments. While polymeric materials remain unaffected by this treatment, silica-based sorbents are at an intrinsic risk of dissolution under high pH conditions, such as, e.g. 0.1M NaOH. It is common misconception that silica-based materials simply cannot be subjected to alkaline conditions above pH 9. Moreover, most studies covering the chemical stability of HPLC sorbents above pH 9 have been limited to the chromatographic conditions used for the separations themselves. Such studies have used buffered mobile phases up to pH 11 or 12. Very little focus has been put on the stability of the stationary phases when subjected to shorter but harsher pH conditions required for regeneration purposes, such as 0.1M NaOH (pH 13). Knowledge about the amount of so-called leachables, degradation products originating from the stationary phase, is of growing importance for the registration of pharmaceuticals for human use and is addressed in this work. This study compares the chemical stability of different commercially available reversed phase silica materials (C18) that are used in industrial scale preparative HPLC. The silica materials were subjected to NaOH regeneration conditions and it is shown that some materials are able to withstand 0.1M NaOH conditions without significant harm. It is demonstrated that contaminants present in the effluent in the range of 10-50 microg/mL can lead to significant contamination of API product fraction.     

Ultrafast electronic and vibrational energy relaxation of Fe(acetylacetonate)3 in solution

Transient mid-infrared spectroscopy is used to probe the dynamics initiated by excitation of ligand-to-metal (400 nm) and metal-to-ligand (345 nm) charge transfer states of FeIII complexed with acetylacetonate (Fe(acac)3, where acac stands for deprotonated anion of acetylacetone) in solution. Transient spectra in the 1500-1600 cm-1 range show two broad absorptions red-shifted from the bleach of the nu(CO) (approximately 1575 cm-1) and nu(C=C) (approximately 1525 cm-1) ground state absorptions. Bleach recovery kinetics has a time constant of 12-19 ps in chloroform and tetrachloroethylene and it decreases by 30-40% in a 10% mixture of methanol in tetrachloroethylene. The transient absorptions experience band narrowing simultaneously with blue-shifting of the absorption maxima. Both phenomena have time constants of 3-9 ps with no evident dependence on the solvent. The experimental observations are ascribed to fast conversion of the initially excited charge transfer states to the ligand field manifold, and subsequent vibrational cooling on the lowest ligand field excited state prior to electronic conversion to the ground state. The analysis of time dependent bandwidths and positions of the transient absorptions provides some evidence of mode specific vibrational cooling.     

An equilibrium analysis of the aqueous H+-MoO4(2-)-(HP)O(3)2- and H+-MoO4(2-)-(HP)O(3)2--HPO4(2-) systems

The speciation in the phosphitomolybdate system, H+-MoO4(2-)-(HP)O(3)2-, has been determined from combined potentiometric and 31P NMR measurements in 0.600 M Na(Cl) medium at 298(1) K. Potentiometric titration data were collected in the ranges 2.5<-log[H+]<6.2, 40.0相似文献   

Electron and energy transfer in donor-acceptor systems with conjugated molecular bridges

Electron and energy transfer reactions in covalently connected donor-bridge-acceptor assemblies are strongly dependent, not only on the donor-acceptor distance, but also on the electronic structure of the bridge. In this article we describe some well characterised systems where the bridges are pi-conjugated chromophores, and where, specifically, the interplay between bridge length and energy plays an important role for the donor-acceptor electronic coupling. For any application that relies on the transport of electrons, for example molecule based solar cells or molecular scale electronics, it will be imperative to predict the electron transfer capabilities of different molecular structures. The potential difficulties with making such predictions and the lack of suitable models are also discussed.     

Synthesis,adsorption and adhesive properties of a cationic amphiphilic block copolymer for use as compatibilizer in composites

In this work, the objective was to synthesize a compatibilizer that can electrostatically adsorb onto cellulose fibers, in fiber-based composites, to enhance the interaction between the fibers and non-polar polymer matrices. This physical route to attach the compatibilizer onto and thereby modify a fiber surface is convenient since it can be performed in water under mild conditions. Polystyrene (PS) was used for the high molecular weight, non-polar, block and poly(dimethylamino)ethyl methacrylate (PDMAEMA) was used as the polar block, which was subsequently quaternized to obtain cationic charges. The block copolymer self-assembles in water into cationic micelles and the adsorption to both silicon oxide surfaces and cellulose model surfaces was studied. The micelles spread out on the surface after heat treatment and contact angle measurements showed that the contact angles against water increased significantly after this treatment. AFM force measurements were performed with a PS probe to study the adhesive properties. The adhesion increased with increasing contact time for the treated surfaces, probably due to entanglements between the polystyrene blocks at the treated surface and the probe. This demonstrates that the use of this type of amphiphilic block copolymer is a promising route to improve the compatibility between charged reinforcing materials, such as cellulose-based fibers/fibrils, and hydrophobic matrices in composite materials.