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61.
间羧基偶氮羧光度法测定痕量铬的研究 总被引:1,自引:0,他引:1
研究了间羧基偶氮羧与Cr2 O2 -7的褪色反应 ,建立了一种新的测定痕量Cr(VI)的光度方法 .发现其在高氯酸介质中具有高灵敏的褪色反应 ,摩尔吸收系数达到 3 .5× 10 6L/mol·cmCr(VI)量在 0~ 48μg范围内符合比尔定律 相似文献
62.
提出了直流示波极谱滴定高含量钼的新方法,在pH为4.5 ̄5.5的乙酸-乙酸铵缓冲溶液中,以Pb(Ⅱ)为滴定剂滴定钼酸根离子,用JP-1A型示波极谱仪作检测器,根据滴定过程中铅波的出现来指示终点的到达。方法简便,快速,结果的准确度,精密度均符合容量分析的要求,适于各类高含量钼矿样中的测定。 相似文献
63.
We report the method of the epitaxial growth of the core–shell ZnTe/ZnMgTe nanowires. The morphology and the crystal structure of several samples grown in different processes have been studied by scanning electron microscopy, high resolution transmission electron microscopy and X-ray diffraction methods. It was shown that the ZnMgTe shell growth was clearly epitaxial with a good crystal quality. The average lattice spacing of the ZnTe cores and ZnMgTe shells have been calculated and Mg content in the shells has been estimated. It was documented that growing the shell lattice mismatched to the core induces the strain in the core. The model of the strain creation mechanism has been proposed. The presence of a shell with a larger energy gap than that of the core results in a strong emission in the spectral region near the band edge. 相似文献
64.
Asim K. Das Sudhin K. Mondal Goutam Mukherjee 《Reaction Kinetics and Catalysis Letters》2001,73(2):257-265
Cetylpyridinium chloride (CPC) inhibits the Cr(VI) oxidation of ethanol and propan-1-ol while sodium dodecyl sulfate (SDS)
catalyzes the title reactions. At higher values of the [surfactant], the rate attains a limiting value. The micellar effect
has been explained by considering the preferential partitioning of the reactants in terms of the suggested mechanism. Applicability
of the Menger-Portnoy model and Piszkiewicz model to explain the observed micellar effect has been examined.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
65.
Reverse scans in square wave voltammetry (SWV) leading to the regeneration of the substance initially present in solution are studied. Widths and peak potentials of waves in SWV performed with both negative and positive potential scans allow us to determine easily the kinetic parameters of a slow electrochemical reaction. The theoretical treatment is verified using the U(V)–U(VI) system in a carbonate medium, which has already been studied by Krulic, Fatouros and Chevalet [J. Electronal. Chem. 251 (1988) 151]. 相似文献
66.
Increasing in the use of various chromium species over the past few decades has inevitably resulted in an increased flux of
their metallic substances in aquatic life. Therefore, experimental work was developed to improve the physical and chemical
characteristics of the prepared mesoporous SiO2–Al2O3 mixed oxides via a sol–gel process. The effective key parameter on the properties of the materials was achieved by the addition
of carboxylate functional group such as Alph-hydroxyl isobuteric acid (AHIBA) during the gelation process and prior the calcinations
step. Better performance of these carboxylate resins are attributed to the complexing ability of the carboxylate groups toward
polyvalent chromium species which is added to the normal sorption properties of the oxides. Urea has been used as a means
of producing an aluminum precipitate that is easier to filter than that produced by rapid addition of base. Introduction of
Al and Si salts together to form mixed oxide modified the way of their substitution in the hosting resin than when they were
separately added. The data revealed that mesoporous materials with very narrow pore diameter distribution (micron-sized) and
high surface area were obtained. The surface areas and pore size distributions were mainly depend on SiO2 content. Systematic investigations were carried out on the set of the prepared mixed oxides with different porosity, cross-linking
degree and exchange loading to find out the best sorbent for chromium removal. The final objective in all cases was aimed
at determining feasible and economically reliable solution to the environmental problems related to the tannery industry. 相似文献
67.
Study of the ZnO crystal growth by vapour transport methods 总被引:5,自引:0,他引:5
R. Tena-Zaera M.C. Martínez-Toms S. Hassani R. Triboulet V. Muoz-Sanjos 《Journal of Crystal Growth》2004,270(3-4):711-721
The crystal growth of ZnO by vapour transport is classically made with the assistance of additional species that produce a gaseous mixture, the role of which remains often uncertain in the transport and growth process. Initially, in order to study the mass transport process, a numerical simulation is made to analyse which are the requirements to have an effective transport. As the pressure of each gaseous species is generally unknown, the numerical study has been performed for different total pressures. It is found that, if congruent and equilibrium conditions are assumed at the sublimation and crystallisation interfaces, effective growth conditions can only be attained for a narrow range of total pressures. Nevertheless, it is well known that ZnO growth by vapour transport is possible for a wide range of pressures of gaseous species. As a consequence, partial pressures higher than the equilibrium ones must be present in order to justify the experimental results. We suggest that the thermal decomposition of ZnO is given by an activated process. The analysis of different mechanisms that could justify the activated decomposition, in accord with a systematic set of growth experiments, suggests that some additional species in the growth of ZnO by vapour transport promote the generation of an additional Zn pressure. This zinc pressure would act autocatalytically inducing O2 and Zn partial pressures higher than the equilibrium ones and promoting thermal decomposition. The above-cited set of experimental growth experiences, that include the presence of C, Zn, Fe, Cu and H2, will be analysed and interpreted according to this approach. 相似文献
68.
Myosin V and myosin VI are two classes of two-headed molecular motors of the myosin superfamily that move processively along helical actin filaments in opposite directions. Here we present a hand-over-hand model for their processive movements. In the model, the moving direction of a dimeric molecular motor is automatically determined by the relative orientation between its two heads at free state and its head‘s binding orientation on track filament.This determines that myosin V moves toward the barbed end and myosin VI moves toward the pointed end of actin.During the moving period in one step, one head remains bound to actin for myosin V whereas two heads are detached for myosin VI: the moving manner is determined by the length of neck domain. This naturally explains the similar dynamic behaviours but opposite moving directions of myosin VI and mutant myosin V (the neck of which is truncated to only one-sixth of the native length). Because of different moving manners, myosin VI and mutant myosin V exhibit significantly broader step-size distribution than native myosin V. However, all the three motors give the same mean step size of -36nm (the pseudo-repeat of actin helix). All these theoretical results are in agreement with previous experimental ones. 相似文献
69.
《Electroanalysis》2017,29(5):1222-1231
A microbial sensor, namely carbon paste electrode (CPE) modified with Citrobacter freundii (Cf–CPE) has been developed for the detection of hexavalent (Cr(VI)) and trivalent (Cr(III)) chromium present in aqueous samples using voltammetry, an electroanalytical technique. The biosensor developed, demonstrated about a twofold higher performance as compared to the bare CPE for the chosen ions. Using cyclic voltammetry and by employing the fabricated Cf–CPE, the lowest limit of detection (LLOD) of 1x10−4 M and 5x10−4 M for Cr(VI) and Cr(III) ions respectively could be achieved. By adopting the Differential Pulse Cathodic Stripping Voltammetric technique, the LLOD could be further improved to 1x10−9 M and 1x10−7 M for Cr(VI) and Cr(III) ions respectively using the biomodified electrodes. The reactions occurring at the electrode surface‐chromium solution interface and the mechanisms of biosorption of chromium species onto the biosensor are discussed. The stability and utility of the developed biosensor for the analysis of Cr(VI) and Cr(III) ions in chromite mine water samples has been evaluated. 相似文献
70.
Polypyrrole nanoparticles of desired structure have been synthesized through simple micelle technique. It is then grafted with functionalized silica gel to develop a novel organic-inorganic hybrid material. The role of dimethyl dichloro silane (coupling agent) in grafting is demonstrated. The nanoparticles are characterized by TEM, SEM and TGA. Grafting reactions are evaluated by spectral (FTIR) analysis and chemical test. The Cr(VI) binding behavior of the composite is studied in various pH of the medium. The selectivity in binding Cr(VI) is monitored. The metal ion adsorption capacity and surface area of the material are found to be 38 mg/g and 235 m2/g, respectively. 相似文献