On-line preconcentration and separation of Co, Ni and Cd via capillary microextraction on ordered mesoporous alumina coating and determination by inductively plasma mass spectrometry (ICP-MS)

In this paper, an ordered mesoporous alumina coating was prepared and applied to capillary microextraction (CME) of trace Co, Ni and Cd for the first time. The coated capillary was used for on-line coupling CME with inductively plasma mass spectrometry (ICP-MS) for the determination of trace metals of Co, Ni and Cd. The porous structure of Al₂O₃ coating was examined by SEM and TEM. The effects of the extraction parameters including pH, sample flow rate and volume, elution solution and interfering ions on the recovery of analytes have been investigated and optimized. Under the optimized conditions, the limits of detection were 0.33, 1.5 and 1.4 ng L⁻¹ for Co, Ni and Cd, respectively, with a preconcentration factor of 10 times. The precisions for all investigated elements were 2.7, 4.1 and 2.5% (c = 0.05 ng L⁻¹, n = 7), for Co, Ni and Cd, respectively, and the sample frequency was 8 h⁻¹.The proposed method was successfully applied for the analysis of trace metals in water, rice and urine samples with the recovery of 94-105%. In order to validate the proposed method, two certified reference materials of GBW 0913 human urine and NIES No.10-b rice flour were analyzed, and the determination values are in good agreement with the certified values. The ordered mesoporous Al₂O₃ coated capillary can be used more than 20 times without decreasing the extraction efficiency.     

新型有序介孔磺酸化酚醛树脂FDU-16-SO3H的合成与酸催化性能

通过氯磺酸磺化有序介孔酚醛树脂(FDU-16)制备了新型有序介孔固体酸催化剂FDU-16-SO₃H. X射线衍射(XRD)、氮气吸附以及透射电镜(TEM)等表征结果表明, 经过磺化后的固体酸催化剂依然保持了高度有序性, 大量的磺酸根基团存在于材料的骨架之中. 在酯化反应和酰基化反应中, 这种新型有序介孔固体酸催化剂表现出比工业树脂和磺酸化介孔二氧化硅等材料更高的催化活性, 这主要归因于它具有较大的比表面积、较强的酸性以及骨架的疏水性.     

Surface composition of ordered intermetallic compounds PtBi and PtPb

The surface composition of bulk electrodes made from the ordered intermetallic phases PtBi and PtPb has been studied by ex-situ X-ray photoelectron spectroscopy (XPS) after being subjected to various electrochemical treatments. Analysis of the freshly polished surfaces showed that in the surface and near surface regions the less-noble metals; Bi and Pb are oxidized to a significant extent (28% and 41%, respectively). Upon cycling to increasingly positive potentials, the fraction of oxidized to metallic forms of Bi and Pb decreased gradually to reach the minimal values of 7% and 6% at +400 mV vs. Ag/AgCl (saturated KCl). The observed decrements are due to leaching of surface oxides; Bi₂O₃ on PtBi and PbCO₃ or Pb(OH)₂ on PtPb. When the potential sweep was extended to more positive values, there was a linear decrease in the surface concentration of the less-noble metal, along with a slight increase in the amount of the species in their oxidized state (Bi₂O₃ for PtBi and PbSO₄ for PtPb). Leaching of Bi from the electrode surface occurs in accordance to the Pourbaix diagram for elemental bismuth, indicating no significant increase in stability arising from the formation of an intermetallic phase with platinum. In the case of PtPb, however, the Pb starts to dissolve away at potentials significantly more positive (+800 mV) than what was anticipated from the Pourbaix diagram. The results obtained here are in accord with our previous observations on the effects of electrochemical pre-treatment on these intermetallic phases for the electrocatalytic oxidation of formic acid and other potential fuel cell fuels.     

Positive solutions of a system of non-autonomous fractional differential equations

Existence of positive solutions for the following system of fractional differential equations:

     

半群的模糊理论研究进展

介绍半群的模糊理论研究的基本内容、方法,重点介绍半群的模糊理想、模糊同余以及目前半群的模糊理论研究进展。     

Neighborhood Unions and Hamilton Cycles in Bipartite Graphs

ＮｅｉｇｈｂｏｒｈｏｏｄＵｎｉｏｎｓａｎｄＨａｍｉｌｔｏｎＣｙｃｌｅｓｉｎＢｉｐａｒｔｉｔｅＧｒａｐｈｓＬｉｕＹｉｐｉｎｇ（刘一平）；ＷｕＺｈｅｎｇｓｈｅｎｇ（吴正声）（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｈｅｍａｔｉｃｓ，ＮａｎｊｉｎｇＮｏｒｍａｌＵｎｉ...     

Quasi-Differential Posets and Cover Functions of Distributive Lattices II: A Problem in Stanley’s <Emphasis Type="Italic">Enumerative Combinatorics</Emphasis>

A distributive lattice L with 0 is finitary if every interval is finite. A function f:₀₀ is a cover function for L if every element with n lower covers has f(n) upper covers. All non-decreasing cover functions have been characterized by the author ([2]), settling a 1975 conjecture of Richard P. Stanley. In this paper, all finitary distributive lattices with cover functions are characterized. A problem in Stanleys Enumerative Combinatorics is thus solved. 2000 Mathematics Subject Classification. 06A07, 06B05, 06D99, 11B39     

PERIODIC BOUNDARY VALUE PROBLEMS FOR IMPULSIVE INTEGRO-DIFFERENTIAL EQUATIONS OF MIXED TYPE IN BANACH SPACES

1.IntroductionInthispaper,weinvestigatetheperiodicboundaryvalueproblem(PBVP)forfirstordernonlinearimpulsiveintegro-differentialeauationsofmixedtypeinaBanachspaceE:wherefEC[JxExExE,E],J=[0,2r]ticECIE,E](k=1,2,',m:KECID,R ],D={(t,s)EJxJ:t2s},HEC[JxJ,R ],R denotesthesetofallnonnegativenumbers,and0相似文献   

A Simple System with Topological Entropy Infinit

Ｌｅｔ（Ｘ，ｄ）ｂｅａｍｅｔｒｉｃｓｐａｃｅ，ａｎｄｆ：Ｘ→Ｘｂｅａｕｎｉｆｏｒｍｌｙｃｏｎｔｉｎｕｏｕｓｍａｐ．Ｗｈｅｎ（Ｘ，ｄ）ｉｓａｃｏｍｐａｃｔｍｅｔｒｉｃｓｐａｃｅ，ｐｅｏｐｌｅｂｅｌｉｅｖｅｔｈａｔｆｈａｓｐｏｓｉｔｉｖｅｔｏｐｏｌｏｇｉ...     

集合函数多目标规划的拉格朗日型对偶定理

本文在［１］的基础上．给出了集合函数多目标规划的拉格朗日型弱对偶定理，严格对偶定理和逆对偶定理．