在含小银粒的掺铕的氟硼酸盐玻璃中等离子体激光的谱带位移

我们提出并讨论了在含分散银粒的氟硼酸盐玻璃中等离子体激光的吸收峰位置随氧化铈浓度而在相当宽的光谱范围内变化的实验观测.     

In situ K-edge X-ray absorption spectroscopy of the ligand environment of single-site Au/C catalysts during acetylene hydrochlorination

The replacement of HgCl₂/C with Au/C as a catalyst for acetylene hydrochlorination represents a significant reduction in the environmental impact of this industrial process. Under reaction conditions atomically dispersed cationic Au species are the catalytic active site, representing a large-scale application of heterogeneous single-site catalysts. While the metal nuclearity and oxidation state under operating conditions has been investigated in catalysts prepared from aqua regia and thiosulphate, limited studies have focused on the ligand environment surrounding the metal centre. We now report K-edge soft X-ray absorption spectroscopy of the Cl and S ligand species used to stabilise these isolated cationic Au centres in the harsh reaction conditions. We demonstrate the presence of three distinct Cl species in the materials; inorganic Cl⁻, Au–Cl, and C–Cl and how these species evolve during reaction. Direct evidence of Au–S interactions is confirmed in catalysts prepared using thiosulfate precursors which show high stability towards reduction to inactive metal nanoparticles. This stability was clear during gas switching experiments, where exposure to C₂H₂ alone did not dramatically alter the Au electronic structure and consequently did not deactivate the thiosulfate catalyst.

In situ chlorine and sulphur XAS shows a dynamic ligand environment around cationic Au single-sites during acetylene hydrochlorination.     

Synthesis and some structural data of nylon 18

The new polyamide nylon 18 was synthesized, mainly to investigate whether a rather large number of methylene groups in the monomeric unit might change the chain packing in comparison with that of lower even nylons. By X-ray diffraction measurements on a mono-oriented fibre, the following crystallographic parameters were found: $\text{a = 4.76}\text{A}\text{?}$; $\text{b = 9.52}\text{A}\text{?}$; $\text{c = 46.9}\text{A}\text{?}$ (fibre axis); γ = 120°. A γ-type packing for the chains was found, similar to that shown by other polyamides of the series.     

Thermal behavior of LDH 2CuAl.CO<Subscript>3</Subscript> and 2CuAl.CO<Subscript>3</Subscript>/Pd

Cu/Al layered double hydroxide (LDH) can be used as a catalyst for important processes such as cross-coupling reactions. This property may be improved by adding palladium by either impregnation or intercalation. Therefore, the LDH matrix and its composites with Pd⁰ or [PdCl₄]^2? have been prepared. By powder X-ray diffraction, FT-infrared spectroscopy, thermogravimetric and elemental analysis it was determined the LDH formula Cu₄Al₂(OH)₁₂CO₃.4H₂O, with malachite as the second phase. The LDH thermal decomposition occurs between 120 and 600 °C, having as intermediates the double oxi-hydroxide and the mixed oxide phases. At 800 °C the residue is composed of CuO and CuAl₂O₄. The composites were obtained employing [PdCl₄]^2? and Pd₂(dba)₃ as precursors, and the solvent choice for this process was shown to be of significant importance: the materials obtained using DMF had Pd impregnated in the surface, while the usage of water promoted the intercalation of [PdCl₄]^2? in the LDH matrix. The thermogravimetric analysis was able to distinguish the mode of supporting palladium between the composites being a reliable characterization for such task.     

Singularity structure of the Hopf bifurcation surface of a differential equation with two delays

We investigated the structure of the so-called first Hopf bifurcation surface associated to a differential equation with two time delays. A geometrical approach leading naturally to a number theoretic approach provides rigourous results which are corroborated by previous numerical and experimental (optical compound resonator) results.     

Bifurcations of periodic trajectories in non-integrable Hamiltonian systems with two degrees of freedom: Numerical and analytical results

Numerical and analytical studies of the types of period n-upling bifurcations undergone by classsical periodic trajectories of non-intergrable Hamiltonians with two degrees of freedom are made. The Hamiltonians studied possess time reversal and reflexion symmetries and we found that these symmetries give rise to additional types of period n-upling bifurcations. The analytical study explains most of the numerically observed bifurcations.     

Effect of Iron Complex Source on MWWTP Effluent Treatment by Solar Photo-Fenton: Micropollutant Degradation,Toxicity Removal and Operating Costs

Benzophenone-3, fipronil and propylparaben are micropollutants that are potential threats to ecosystems and have been detected in aquatic environments. However, studies involving the investigation of new technologies aiming at their elimination from these matrices, such as advanced oxidation processes, remain scarce. In this study, different iron complexes (FeCit, FeEDTA, FeEDDS and FeNTA) were evaluated for the degradation of a mixture of these micropollutants (100 µg L⁻¹ each) spiked in municipal wastewater treatment plant (MWWTP) effluent at pH 6.9 by solar photo-Fenton. Operational parameters (iron and H₂O₂ concentration and Fe/L molar ratio) were optimized for each complex. Degradation efficiencies improved significantly by increasing the concentration of iron complexes (1:1 Fe/L) from 12.5 to 100 µmol L⁻¹ for FeEDDS, FeEDTA and FeNTA. The maximum degradation reached with FeCit for all iron concentrations was limited to 30%. Different Fe/L molar ratios were required to maximize the degradation efficiency for each ligand: 1:1 for FeNTA and FeEDTA, 1:3 for FeEDDS and 1:5 for FeCit. Considering the best Fe/L molar ratios, higher degradation rates were reached using 5.9 mmol L⁻¹ H₂O₂ for FeNTA and FeEDTA compared to 1.5 and 2.9 mmol L⁻¹ H₂O₂ for FeEDDS and FeCit, respectively. Acute toxicity to Canton S. strain D. melanogaster flies reduced significantly after treatment for all iron complexes, indicating the formation of low-toxicity by-products. FeNTA was considered the best iron complex source in terms of the kinetic constant (0.10 > 0.063 > 0.051 > 0.036 min⁻¹ for FeCit, FeNTA, FeEDTA and FeEDDS, respectively), organic carbon input and cost-benefit (USD 327 m⁻³ > USD 20 m⁻³ > USD 16 m⁻³ > USD 13 m⁻³ for FeEDDS, FeCit, FeEDTA and FeNTA, respectively) when compared to the other tested complexes.     

Some theoretical investigations in crystal field theory

General expressions for the crystal field parameters are established by the introduction of an electronic charge density which depends on the operator Ô(n) = |ψ _n >< ψ _n |, where |ψ _n > is an eigenstate of the system (central ion + ligands). The connection with molecular orbital theory is discussed as well as the expected behaviour of the crystal field parameters with the eigenstates |ψ _n > for the case of both weak and strong field. Especially in the former case, simple expressions are obtained for the correlation crystal field parameters.     

A theoretical interpretation of the abnormal D0→F4 intensity based on the Eu local coordination in the Na9[EuW10O36]·14H2O polyoxometalate

The Na₉[EuW₁₀O₃₆]·14H₂O polyoxometalate studied here has shown a peculiar 4f-4f emission spectrum that has two main differences in comparison to data reported previously in the literature: a ⁵D₀→⁷F₀ line with much smaller intensity and an abnormally high intensity of the ⁵D₀→⁷F₄ transition. These results have been theoretically interpreted in terms of the Ω_λ intensity parameters and their dependence on the nature and local symmetry of the chemical environment around the Eu³⁺ ion, leading to the conclusion that the chemical environment is highly polarizable with a local symmetry corresponding to a slightly distorted D_4d coordination geometry. Further evidences corroborating this interpretation were obtained by progressively dissolving the polyoxometalate in water, inducing a progressive accommodation of the coordination polyhedron towards lower symmetries.     

Luminescent Properties of Some Rare Earth Phosphates

Abstract

Luminescent properties of scandium and yttrium phosphates are discussed and mechanisms involving their emissions proposed.