Nanocrystals for large Stokes shift-based optosensing

The influence of Stokes shift in optosensing was discussed. Then, the current status of large Stokes shift-based optosensing was reviewed here.     

Length of the flooded zone in the column inlet and evaluation of different retention gaps for capillary gas chromatography

In on-column or in splitless injection with recondensation of the solvent, the length of the flooded zone in the column inlet depends primarily on the wettability of the internal wall of the inlet. For columns with a coated inlet this explains why peak distortion due to band broadening in space by a certain sample volume is pronounced in one case and hardly observable in another. Glass or fused silica capillaries silylated with diphenyltetramethyldisilazane were found to give optimal retention gaps. They combine thorough and thermostable deactivation with good wettability and low retention power. On the other hand it is very easy to deactivate fused silica capillaries with Carbowax. The resulting retention gaps are suitable for a wide range of applications and are particularly attractive for the analysis of dirty samples which require frequent replacement of the inlet.     

Origin of visible-light-driven photocatalysis: A comparative study on N/F-doped and N-F-codoped TiO2 powders by means of experimental characterizations and theoretical calculations

An overall comparative study was carried out on N-doped, F-doped, and N-F-codoped TiO₂ powders (NTO, FTO, NFTO) synthesized by spray pyrolysis in order to elucidate the origin of their visible-light-driven photocatalysis. The comparisons in their experimentally obtained characteristics were based on the analysis of XPS, UV-Vis, PL, NH₃-TPD and ESR spectra. The comparisons in their theoretically predicted properties were based on the analysis of the calculated electronic structures. As the results, N-doping into TiO₂ resulted in not only the improvement in visible-light absorption but also the creation of surface oxygen vacancies. F-doping produced several beneficial effects including the creation of surface oxygen vacancies, the enhancement of surface acidity and the increase of Ti³⁺ ions. Doped N atoms formed a localized energy state above the valence band of TiO₂, whereas doped F atoms themselves had no influence on the band structure. The photocatalytic tests indicated that the NFTO demonstrated the highest visible-light activity for decompositions of both acetaldehyde and trichloroethylene. This high activity was ascribed to a synergetic consequence of several beneficial effects induced by the N-F-codoping.     

内含式化合物X@B12P12的结构与稳定性研究

采用B3LYP/6-31G*方法，对内含式化合物X@B₁₂P₁₂(X=Li^0/+、Na^0/+、K^0/+、Be^0/2+、Mg^0/2+、Ca^0/2+、H和He)的不同对称性构型进行了计算，讨论其最稳定构型的几何参数、布居分析、偶极矩、电离势、包含能、振动频率、能隙和自旋密度． 发现在X@B₁₂P₁₂化合物中，客体X=Li、Na^0/+、K^0/+、Mg^0/2+、Ca^0/2+和He处在偏离笼的中心0.006 nm的半径内． Be²⁺沿着C₃轴偏离中心点0.279 nm． 在Be@B₁₂P₁₂和H@B₁₂P₁₂的基态结构中，Be和H与笼上的B原子成键． 除Li@B₁₂P₁₂、 Be²⁺@B₁₂P₁₂和He@ B₁₂P₁₂外， 其余结构为C_s对称稳定构型．     

Band splitting in overloaded isocratic elution chromatography I. The experimental evidence

A series of samples of increasing volume (from 0.001 to 4.0 cm3), containing the same constant concentration (40 g/l) of two simple compounds, ethylbenzoate and 4-tert.-butylphenol were injected on a Kromasil-C18 column with methanol-water (62:38. v/v) as the mobile phase. Complex band profiles were observed when the volume of the sample became large enough and strong band interference took place. The analysis of the fractions collected during the elution of the mixed band demonstrates that, for samples larger than 2 cm3, the band of 4-tert.-butylphenol is split into two separate bands, one eluted before and the other eluted after the band of ethylbenzoate. Such a phenomenon has never been observed yet in RPLC, under isocratic elution conditions.     

Structure,Chemical Bonding,and Properties of Sc2Ni2In

Sc₂Ni₂In was prepared by a reaction of the elemental components in an are furnace and subsequent annealing at 1070 K. Sc₂Ni₂In is a Pauli paramagnet and a poor metallic conductor with a specific resistivity of 224 mΩcm at room temperature. Its crystal structure was refined from X-ray powder data: P4/mbm, a = 716.79(1) pm, c = 333.154(8) pm, Z = 2, R_wp = 0.040, and R_B(I) = 0.026. Sc₂Ni₂In crystallizes with a ternary ordered version of the U₃Si₂-type structure. The nickel and indium atoms occupy [NiSc₆] trigonal prisms and [InSc₈] square prisms, respectively. These structural fragments are derived from the AlB₂ and CsCl-type structures. Semi-empirical band structure calculations reveal Sc₂Ni₂In to be a nickelide, and the strongest bonding interactions are found for the Sc? Ni contacts, followed by Sc? In and Ni? In. A rigidband model suggests the existence of the isotypic phase Sc₂Ni₂Sb.     

Ternary silicides M2Cr4Si5 (M=Ti, Zr, Hf): filled variants of the Ta4SiTe4 structure type

The isostructural ternary silicides M₂Cr₄Si₅ (M=Ti, Zr, Hf) were prepared by arc-melting of the elemental components. The single-crystal structure of Zr₂Cr₄Si₅ was determined by X-ray diffraction (Pearson symbol oI44, orthorhombic, space group Ibam, Z=4, a=7.6354(12) Å, b=16.125(3) Å, c=5.0008(8) Å). Zr₂Cr₄Si₅ adopts the Nb₂Cr₄Si₅-type structure, an ordered variant of the V₆Si₅-type structure. It consists of square antiprisms that have Zr and Cr atoms at the corners and Si atoms at the centers; they share opposite faces to form one-dimensional chains _∞¹[Zr_4/2Cr_4/2Si] surrounded by additional Si atoms and extending along the c direction. In a new interpretation of the structure, additional Cr atoms occupy interstitial octahedral sites between these chains, clarifying the relation between this structure and that of Ta₄SiTe₄. The formation of short Si-Si bonds in Zr₂Cr₄Si₅ is contrasted with the absence of Te-Te bonds in Ta₄SiTe₄. The compounds M₂Cr₄Si₅ (M=Ti, Zr, Hf) exhibit metallic behavior and essentially temperature-independent paramagnetism. Bonding interactions were analyzed by band structure calculations, which confirm the importance of Si-Si bonding in these metal-rich compounds.     

Analysis of petroleum fractions by on-line micro HPLC-HRGC coupling,involving increased efficiency in using retention gaps by partially concurrent solvent evaporation

Two-dimensional chromatography of gasoline by on-line coupled HPLC-HRGC, as described in this paper, allows separate GC analysis of paraffins and aromatics. The GC system contains a retention gap of only 10 m length for introducing HPLC fractions of 100 μl volume. This becomes possible through evaporation of part of the solvent during introduction of the HPLC eluent. This “partially concurrent solvent evaporation” technique allows transfer of large volumes of HPLC eluent into relatively short retention gaps, maintaining the full efficiency of the solvent effects in reconcentrating the bands of the early eluted solutes.     

Optical and Electrical Properties of Polymerizing Plasmas and Their Correlation with DLC Film Properties

Diamond-like carbon (DLC) films were grown from radiofrequency plasmas of acetylene-argon mixtures, at different excitation powers, P. The effects of this parameter on the plasma potential, electron density, electron temperature, and plasma activity were investigated using a Langmuir probe. The mean electron temperature increased from about 0.5 to about 7.0 eV while the mean electron density decreased from about 1.2 × 10⁹ to about 0.2 × 10⁹ cm^–3 as P was increased from 25 to 150 W. Both the plasma potential and the plasma activity were found to increase with increasing P. Through actinometric optical emission spectrometry, the relative concentrations of CH, [CH], and H, [H], in the discharge were mapped as a function of the applied power. A rise in [H] and a fall in [CH] with increasing P were observed and are discussed in relation to the plasma characteristics and the subimplantation model. The optical properties of the films were calculated from ultraviolet-visible spectroscopic data; the surface resistivity was measured by the two-point probe method. The optical gap, E _G, and the surface resistivity, _s, fall with increasing P. E _G and _s are in the ranges of about 2.0–1.3 eV and 10¹⁴–10¹⁶ /, respectively. The plasma power also influences the film self-bias, V _b, via a linear dependence, and the effect of V _b on ion bombardment during growth is addressed together with variation in the relative densities of sp² and sp³ bonds in the films as determined by Raman spectroscopy.