Kinetics of no decomposition over Cu/ZSM-5 catalyst

The kinetics of catalytic decomposition of NO over Cu/ZSM-5 catalyst has been studied in an integral flow reactor at atmospheric pressure. Kinetic analysis is based on the assumption that the surface reaction represents the rate-determining step. On the basis of theoretical considerations of different interactions between reactants and catalyst, and experimental evidences, three different mechanistic kinetic models were chosen. Also a power-law model was tested. The best agreement has been achieved with the model

微波萃取/GC-MS法对电子电气产品中多氯萘的测定

建立了微波萃取/GC-MS法检测电子电气产品中多氯萘的方法。将破碎后的样品以甲苯为溶剂进行微波萃取,萃取液经硅胶小柱净化、平行蒸发定量浓缩后采用气相色谱-质谱法测定多氯萘的含量,外标法定量。优化了样品前处理条件,包括前处理方式、微波萃取溶剂、萃取时间,以及净化小柱的选择。对于8种含不同氯原子数的多氯萘,在1~50 mg/L范围内,线性关系良好,相关系数均大于0.995;方法定量下限为0.2~1.0 mg/kg,相对标准偏差为2.7%~7.2%,回收率为77%~112%。该法操作简便、分析迅速、结果准确,可以满足对电子电气产品中多氯萘的定性确证和定量分析。     

Synthesis and thermal behavior of a novel UV‐curable transparent flame retardant film and phosphorus‐nitrogen synergism of flame retardancy

A novel phosphorus monomer (PDHA) has been synthesized through phenyl dichlorophosphate (PDPC) reacting with 2‐hydroxyethyl acrylate (HEA). The structure of PDHA was characterized by Fourier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance spectroscopy (¹H NMR). A series of UV curable resins were manufactured by blending PDHA with triglycidyl isocyanurate acrylate (TGICA) at different weight ratios. The fire performance was examined by micro‐scale combustion calorimeter (MCC) and limiting oxygen index (LOI). The results obtained from MCC indicated that the addition of PDHA to TGICA reduced the HRR and HRC. In addition, the LOI values varied from 28 to 34. The char residues of the composites were observed by scanning electron microscopy (SEM). Their thermal degradation behavior was investigated by thermogravimetric analysis and real time FTIR analysis (RT‐FTIR). The test results indicated that when the weight ratio of PDHA/TGICA = 1:1, the onset temperature of the composite was highest and the most char residue at 700°C was observed. RT‐FTIR showed that the phosphate group of PDHA first degraded to form poly(phosphoric acid)s at around 300°C, which had the major contribution to form the compact char to protect the sample from further degradation. Copyright © 2010 John Wiley & Sons, Ltd.     

The Effects of Salts on the Room-Temperature Fluorescence and Room-Temperature Phosphorescence of Tetrols on Filter Paper and Filter Paper with Silicone

Abstract

Several salts were investigated to enhance the room-temperature solid-matrix phosphorescence of the four stereoisomeric tetrols on filter paper. Thallium acetate was found to enhance the phosphorescence to the greatest extent, but it was necessary to prepare the thallium acetate in an acetic acid solution to achieve the maximum phosphorescence from the solid matrix. Also, thallium acetate essentially quenched the solid-matrix fluorescence of the tetrols. Without thallium acetate adsorbed on filter paper, strong room-temperature fluorescence signals were observed from the tetrols adsorbed on filter paper. With a new solid matrix, filter paper which contained silicone, no heavy-atom was needed to obtain strong phosphorescence from the adsorbed tetrols. In fact, the room-temperature fluorescence from the tetrols adsorbed on this type of filter paper was very strong. The room-temperature fluorescence gave a limit of detection in the sub-picogram range for one of the tetrols with the silicone treated filter paper.     

The gas phase structures of the isomers of benzene: IV. Hexafluoro-dewar-benzene

Gas phase electron diffraction data for HFDB were analyzed, following conventional procedures, and a structure was deduced for the perfluoro-bicyclo-[2.2.0]hexa-2,5-diene consistent with its C_2v symmetry. A least squares analysis of the molecular scattering function gave the following r_g values: [-C-C-] = 1.597 ± 0.006 Å, [C-C-] = 1.503 ± 0.002 Å, [-C-C-] = 1.356 ± 0.007 Å, [-C-F](bridge) = 1.331 ± 0.008 Å, [-C-F] (terminal) = 1.323 ± 0.004 Å. The flap angle between the rings is 115.3( ± .7)°. The terminal fluorines are in the planes of the corresponding rings.The most notable feature of the structure is the long C-C bridge bond, which was also observed in hexamethyl-Dewar-benzene. The geometrical features of HFDB are compared with corresponding ones in HMDB, and with perfluoro- cyclobutene as well as with theoretical estimates.     

An improved colorimetric method for chlorine dioxide and chlorite ion in drinking water using lissamine green B and horseradish peroxidase

Lissamine Green B (LGB) was carefully selected as a potential candidate for the development of a new U.S. Environmental Protection Agency (EPA) method that is intended for use at water utilities to determine chlorine dioxide (ClO₂) in drinking water. Chlorine dioxide reacts with LGB in aqueous solution to decrease the absorbance of LGB in direct proportion to the ClO₂ concentration. LGB was confirmed to have adequate sensitivity, and to suffer less interference than other dyes reported in the literature. The stoichiometry for the reaction between LGB and ClO₂ was found not to be 1:1 and is dependent on the LGB concentration. This required calibration of each LGB stock solution and prompted the investigation of alternate means of calibration, which utilized a horseradish peroxidase (HRP)-catalyzed conversion of chlorite ion (ClO₂⁻) to ClO₂. This approach allowed the simultaneous determination of ClO₂⁻ concentration, which is also required each day at water plants that use ClO₂. Studies were conducted to characterize and carefully optimize the HRP-conversion of ClO₂⁻ to ClO₂ in order to yield reaction conditions that could be accomplished in less than 30 min at modest cost, yet meet EPA's sensitivity and robustness requirements for routine monitoring. An assessment of method detection limit, linearity and slope (or sensitivity), precision, and accuracy in finished drinking water matrices indicated that this approach was suitable for publication as EPA Method 327.0.     

The Triplet State in Pyrene

Both emission and excitation spectra of phosphorescence and delayed fluorescence of pyrene single crystals have been investigated between 2 K and 300 K using cw dye laser excitation. The experiments prove that the lowest triplet state is excitonic in nature in the high and low temperature crystalline phases. No evidence for triplet excimer emission could be found. The so-called regular broad band triplet excimer emission was spectrally resolved at low temperature and identified as trap emission. On the basis of polarized high resolution excitation spectra of undoped normal and perdeuterated pyrene (supplemented by Zeeman spectra at helium temperature) and the concentration dependent phosphorescence excitation spectra of isotopically mixed crystals the triplet state symmetry and the excitonic Davydov splitting of the low temperature crystalline phase was determined. The resonance pair interaction between the dimer molecules was found to be an order of magnitude smaller than predicted from calculations reported so far.     

Structural change of liquid Si15Te85 and Si20Te80 with temperature: Ab initio molecular dynamics simulations

Using ab initio molecular dynamics simulations, the structural and electronic properties of liquid Si₁₅Te₈₅ and Si₂₀Te₈₀ at two temperatures were studied respectively. Compared with available experimental data, the calculated structure factors are acceptable. From symmetry arguments, the calculated partial bond-angle distribution functions suggest that with increasing temperature the extensive tetrahedral network structures persist longer in liquid Si₂₀Te₈₀ than those do in liquid Si₁₅Te₈₅. Our results indicate that the local tetrahedral structure around Si atoms and the Peierls-like distorted local atomic structure around Te atoms both play important roles in the structural change of liquid Si₂₀Te₈₀ and Si₁₅Te₈₅, which also suggest that the mechanisms of the structural change upon cooling in liquid Si₂₀Te₈₀ and Si₁₅Te₈₅ are of no essential difference. The results of DOS and LDOS indicate that the variation of the dip in DOS at E_F mainly results from the change of Te p orbitals.     

Spinnablity and structure characterization of mullite fibers via sol–gel-ceramic route

Viscosity and rheology behaviors of the mullite sols prepared from aqueous solution of aluminum nitrate, aluminum isopropoxide and tetraethylorthosilicate has been investigated. Rheological measurement suggested that mullite sols exhibited good spinniabilty when the evaporation of the solvent is allowed during sol–gel process. Spinnable sols showed shear-thinning flow behavior with high viscosity to the time of gelation. By adjusting temperature, the gelation degree and viscosity of the sol could be stabilized at a certain value and the sol–gel transition could be transferred to the spinning line of a laboratory dry-spinning apparatus. Continuous mullite fibers were obtained from such sols using sol gel dry-spinning method. The final ceramic fibers had smooth surfaces with an average diameter of 50 μm. Structure evolution of mullite ceramic fibers were characterized by MAS NMR and specific surface area analyses.