Noninvasive monitoring of photocatalytic degradation of X‐ray contrast media using Raman spectrometry

The photocatalytic degradation of the X‐ray contrast agents iohexol and diatrizoate are monitored by in situ Raman spectrometry measurements in aqueous solution with a TiO₂ photocatalyst. Spectral features and changes are interpreted with the use of density functional theory calculations. While we observe similar results to those published previously, significant changes seen in the Raman spectrum allow us to better identify the mechanisms without the need for deductive approaches or complicated sample preparation. Diatrizoate spectra are consistent with hydroxyl radical attack leading to the loss of CO₂. Iohexol is more difficult to interpret, representing a current challenge to the use of Raman spectrometry for real‐time monitoring of photocatalytic degradation experiments. We explore internal standards that can be added to gauge overall degradation rates to some extent. Potential extensions of the work are described, particularly in terms of increased rate of data acquisition and more general application. Copyright © 2013 John Wiley & Sons, Ltd.     

Homo‐ and Heteronuclear Compounds with a Symmetrical Bis‐hydrazone Ligand: Synthesis,Structural Studies,and Luminescent Properties

Nine new coordination compounds have been synthesized by the reaction of salts of bivalent metal ions (a=Zn^II, b=Cu^II, c=Ni^II, d=Co^II) with the bis(benzoylhydrazone) derivative of 4,6‐diacetylresorcinol (H₄L). Three kinds of complexes have been obtained: homodinuclear compounds [M₂(H₂L)₂]?nH₂O ( 1 a , 1 b , 1 c , and 1 d ), homotetranuclear compounds [M₄(L)₂]?n(solv) ( 2 a and 2 c ), and heterotetranuclear compounds [Zn₂M₂(L)₂]?n(solv) ( 2 ab , 2 ac , and 2 ad ). The structures of the free ligand H₄L?2 DMSO and its complexes [Zn₂(H₂L)₂(DMSO)₂] ( 1 a* ), [Zn₄(L)₂(DMSO)₆] ( 2 a* ), and [Zn_0.45Cu_3.55(L)₂(DMSO)₆]?2 DMSO ( 2 ab* ) were elucidated by single‐crystal X‐ray diffraction. The ligand shows luminescence properties and its fluorimetric behavior towards M^II metals (M=Zn, Cu, Ni and Co) has been studied. Furthermore, the solid‐state luminescence properties of the ligand and compounds have been determined at room temperature. ¹H NMR spectroscopic monitoring of the reaction of H₄L with Zn^II showed the deprotonation sequence of the OH/NH groups upon metal coordination. Heteronuclear reactions have also been monitored by using ESI‐MS and spectrofluorimetric techniques.     

The effects of fabrication and annealing on the structure and hydrogen permeation of Pd–Au binary alloy membranes

The addition of gold to palladium membranes produces many desirable effects for hydrogen purification, including improved tolerance of sulfur compounds, reduction in hydride phase formation, and, for certain compositions, improved hydrogen permeability. The focus of this work is to determine if sequential plating can be used to produce self-supported alloy membranes with equivalent properties to membranes produced by conventional metallurgical techniques such as cold-working.Sequential electroplating and electroless plating were used to produce freestanding planar Pd–Au membranes with Au contents ranging from 0 to 20 wt%, consisting of Au layers on both sides of a pure Pd core. Membranes were characterized by single-gas permeation measurements, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), and high temperature, controlled-atmosphere XRD (HTXRD). Sequentially plated foils tested without any prior annealing had significantly lower H₂ permeabilities than either measured or literature values for homogeneous foils of equivalent composition. This effect appears to be due to the formation of stable gold-enriched surface layers. Pretreatment of membranes to 1023 K created membranes with hydrogen permeabilities equivalent to literature values, despite the fact that trace amounts of surface gold remained detectable with XRD.     

An elliptic system with bifurcation parameters on the boundary conditions

In this paper we consider the elliptic system Δu=a(x)upvq, Δv=b(x)urvs in Ω, a smooth bounded domain, with boundary conditions , on ∂Ω. Here λ and μ are regarded as parameters and p,s>1, q,r>0 verify (p−1)(s−1)>qr. We consider the case where a(x)?0 in Ω and a(x) is allowed to vanish in an interior subdomain Ω₀, while b(x)>0 in . Our main results include existence of nonnegative nontrivial solutions in the range 0<λ<λ₁?∞, μ>0, where λ₁ is characterized by means of an eigenvalue problem, and the uniqueness of such solutions. We also study their asymptotic behavior in all possible cases: as both λ,μ→0, as λ→λ₁<∞ for fixed μ (respectively μ→∞ for fixed λ) and when both λ,μ→∞ in case λ₁=∞.     

Magnetic Resonance Imaging of Water Content and Flow Processes in Natural Soils by Pulse Sequences with Ultrashort Detection

Magnetic resonance imaging is a valuable tool for three-dimensional mapping of soil water processes due to its sensitivity to the substance of interest: water. Since conventional gradient- or spin-echo based pulse sequences do not detect rapidly relaxing fractions of water in natural porous media with transverse relaxation times in the millisecond range, pulse sequences with ultrafast detection open a way out. In this work, we compare a spin-echo multislice pulse sequence with ultrashort (UTE) and zero-TE (ZTE) sequences for their suitability to map water content and its changes in 3D in natural soil materials. Longitudinal and transverse relaxation times were found in the ranges around 80 ms and 1 to 50 ms, respectively, so that the spin echo sequence misses larger fractions of water. In contrast, ZTE and UTE could detect all water, if the excitation and detection bandwidths were set sufficiently broad. More precisely, with ZTE we could map water contents down to 0.1 cm³/cm³. Finally, we employed ZTE to monitor the development of film flow in a natural soil core with high temporal resolution. This opens the route for further quantitative imaging of soil water processes.     

Substitutional and positional disorder in Sr2.88Cu3.12(PO4)4

The title compound, a hydrothermally synthesized strontium copper(II) phosphate(V) (2.88/3.12/4), is isotypic with Sr₃Cu₃(PO₄)₄, obtained previously by solid‐state reaction, but not with Sr₃Cu₃(PO₄)₄, obtained previously by the hydrothermal method. A surplus of copper was observed by both structural and chemical analysis, and the formula obtained by the structural analysis is in full agreement with results of the EDX (energy‐dispersive X‐ray diffraction) analysis. The structure consists of layers of Cu₃O₁₂ groups which are linked via the PO₄ tetrahedra. The Cu₃O₁₂ groups are formed by one Cu1O₄ and two Cu2O₅ coordination polyhedra sharing corners. The central Cu1 atom of the Cu₃O₁₂ group is located at an inversion centre (special position 2a). The unique structural feature of the title compound is the presence of 12% Cu in the Sr1 site (special position 2b, site symmetry ). Moreover, disordered Sr2 atoms were observed: a main site (Sr2a, 90%) and a less occupied site (Sr2b, 10%) are displaced by 0.48 (3) Å along the b axis. Such substitutional and positional disorder was not observed previously in similar compounds.     

Large solutions to an anisotropic quasilinear elliptic problem

In this paper we consider existence, asymptotic behavior near the boundary and uniqueness of positive solutions to the problem ${\rm div}_x (|\nabla_x u|^{p-2}\nabla_xu)(x,y) + {\rm div}_y (|\nabla_y u|^{q-2}\nabla_y u) (x, y) = u^r(x, y)$ in a bounded domain ${\Omega \subset \mathbb{R}^N \times \mathbb{R}^M}In this paper we consider existence, asymptotic behavior near the boundary and uniqueness of positive solutions to the problem

divx (|?x u|p-2?xu)(x,y) + divy (|?y u|q-2?y u) (x, y) = ur(x, y){\rm div}_x (|\nabla_x u|^{p-2}\nabla_xu)(x,y) + {\rm div}_y (|\nabla_y u|^{q-2}\nabla_y u) (x, y) = u^r(x, y)      150. An Unprecedented Blueshifted Naphthalimide AIEEgen for Ultrasensitive Detection of 4‐Nitroaniline in Water via “Receptor‐Free” IFE Mechanism      Mst Nasima Khatun  Arvin Sain Tanwar  Niranjan Meher  Parameswar Krishnan Iyer 《化学:亚洲杂志》2019,14(24):4725-4731 The development of a new naphthalene appended naphthalimide derivative ( NMI ) with aggregation‐induced enhanced emission (AIEE) property for the sensitive detection of 4‐nitroaniline (4‐NA) in aqueous media is presented here. The newly designed naphthalimide AIEEgen has an exceptional blue‐shifted condensed state emission that is devoid of any receptor site, accomplished ultrasensitive detection of 4‐NA, which is one of the broad‐spectrum pesticides that belong to the class III toxic chemical, at parts per billion level (LOD/36 ppb, Ksv=4.1×104 m ?1) in water with excellent selectivity even in the presence of potentially competing aliphatic and aromatic amines. The reported probe is the first of its kind, demonstrating major advantages of receptor‐free inner filter effect (IFE) mechanism for the sensitive detection of 4‐NA using an AIEEgenic probe. Excellent sensitivity for 4‐NA is also achieved on paper‐based test‐strip for low‐cost on‐site detection.      [首页] « 上一页 [10] [11] [12] [13] [14] 15 [16] [17] [18] [19] [20] 下一页 » 末  页»

An Unprecedented Blueshifted Naphthalimide AIEEgen for Ultrasensitive Detection of 4‐Nitroaniline in Water via “Receptor‐Free” IFE Mechanism

The development of a new naphthalene appended naphthalimide derivative ( NMI ) with aggregation‐induced enhanced emission (AIEE) property for the sensitive detection of 4‐nitroaniline (4‐NA) in aqueous media is presented here. The newly designed naphthalimide AIEEgen has an exceptional blue‐shifted condensed state emission that is devoid of any receptor site, accomplished ultrasensitive detection of 4‐NA, which is one of the broad‐spectrum pesticides that belong to the class III toxic chemical, at parts per billion level (LOD/36 ppb, K_sv=4.1×10⁴ m ^?1) in water with excellent selectivity even in the presence of potentially competing aliphatic and aromatic amines. The reported probe is the first of its kind, demonstrating major advantages of receptor‐free inner filter effect (IFE) mechanism for the sensitive detection of 4‐NA using an AIEEgenic probe. Excellent sensitivity for 4‐NA is also achieved on paper‐based test‐strip for low‐cost on‐site detection.