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71.
A method for the direct determination of volatile and non-volatile nickel and vanadium compounds in crude oil without previous treatment using direct solid sampling graphite furnace atomic absorption spectrometry is proposed. The crude oil samples were weighed directly onto solid sampling platforms using a microbalance and introduced into a transversely heated solid sampling graphite tube. In previous work of our group losses of volatile nickel and vanadium compounds have been detected, whereas other nickel and vanadium compounds were thermally stable up to 1300 and 1600 °C, respectively. In order to avoid this problem different chemical modifiers (conventional and permanent) have been investigated. With 400 μg of iridium as permanent modifier, the signal started to drop already after two atomization cycles, possibly because of an interaction of nickel (which is a catalyst poison) with iridium. Twenty micrograms of palladium applied in each determination was found to be optimum for both elements. The palladium was deposited on the platform and submitted to a drying step at 150 °C for 75 s. After that the sample was added onto the platform and submitted to the furnace program. The influence of sample mass on the linearity of the response and on potential measurement errors was also investigated using four samples with different nickel content. For the sample with the lowest nickel concentration the relationship between mass and integrated absorbance was found to be non-linear when a high sample mass was introduced. It was suspected that the modifier had not covered the entire platform surface, which resulted in analyte losses. This problem could be avoided by using 40 μL of 0.5 g L−1 Pd with 0.05% Triton X-100. Calibration curves were established with and without modifier, with aqueous standards, oil-in-water emulsions and the certified reference material NIST SRM 1634c (trace metals in residual fuel oil). The sensitivity for aqueous standards and emulsions was close to that for SRM 1634c, making possible the use of aqueous standards for calibration. The limits of detection and quantification obtained for nickel and vanadium under this condition were found to be 0.02 and 0.06 μg g−1, respectively, for both elements, based on 10 mg of sample. Nickel and vanadium were determined in the samples with (total Ni and V) and without the use of Pd (thermally stable compounds), and the concentration of volatile compounds was calculated by difference. The results were compared with those obtained by high-resolution continuum source graphite furnace atomic absorption spectrometry by emulsion technique; no significant differences were found for total Ni and V at the 95% confidence level according to a Student's t-test. 相似文献
72.
ADSORPTION OF 2,4-DICHLOROBENZOXYACETIC ACID ONTO HYPERCROSSLINKED RESIN MODIFIED BY PHENOLIC HYDROXYL GROUP (AM-1) 总被引:2,自引:0,他引:2
INTRODUCTIONAdsorption has been considered to be the best available technology for removing organics from water in the USSafe Drinking Water Act[1]. Due to many drawbacks of activated carbon[2-7], the most widely used adsorbent,hypercrosslinked polymeric adsorbents developed by Tsyurupa and Davankov[8] have been increasingly viewedas an alternative to activated carbon for selective removal of specific organic substances from contaminatedwater[9-12], and series of researches have been do… 相似文献
73.
Excitation energies of 123 polycyclic aromatic hydrocarbons were calculated by incorporating the improved method of new-γ for the two-center electron repulsion integral into two semiempirical molecular orbital methods (CNDO/S and INDO/S). This variable method well reproduced experimental excitation energies of them. The average error of the improvement is about 0.162 (CNDO/S) or 0.237 eV (INDO/S) though the average error without the improvement is about 0.541 (CNDO/S) or 0.536 eV (INDO/S). The improvement was useful for the calculations of other organic compounds including hetero atoms, such as organic dye. 相似文献
74.
75.
Alkaline-earth (Ae) metals have attracted a wealth of interdependent research from synthetic chemists. In Ae-catalyzed organometallic reactions, β-diketiminate is a typical ligand used to stabilize Ae catalysts by forming six-membered rings comprising Ae metals. Herein, studies focusing on the configuration of β-diketiminate-coordinated Ae compounds observed that the CC and CN bonds are homogeneous and unchanged. Furthermore, energetic studies observed that the formation of the Ae-incorporated six-membered rings results in enhanced stability of >20 kcal/mol. The nucleus-independent chemical shifts, anisotropy of the induced current density, and molecular orbital analyses demonstrated the non-aromaticity of the β-diketiminate-coordinated Ae compounds. The improved stability of these compounds can be explained by the delocalization of the π electrons derived from the β-diketiminate moiety. 相似文献
76.
SAPO-5,-11和-34分子筛模板剂的脱除及其结构的热致变化 总被引:2,自引:0,他引:2
用水热法合成了SAPO-5,-11和-34硅磷酸铝类分子筛。并对经不同温度焙烧处理的样品进行表征,结果表明:分子筛中模块剂的热分解过程与其结构和孔大小有较大的关系。在SAPO-5和SAPO-34分子筛中,外部联接的T-O-T键的反对称伸缩振动峰(1240cm~(-1)-1038cm~(-1))和其对称伸缩振动(734cm~(-1)-600cm~(-1))及双环的变形振动(600-500cm~(-1))的吸收峰对样品的结晶度比较敏感。但在SAPO-11中,分子筛骨架中T-O-T反对称伸缩振动(1225cm~(-1)和1038cm~(-1))随结晶度的下降而基本保持不变,但内四面体(TO_4)的对称伸缩振动,反对称伸缩振动峰及T-O弯曲振动峰随样品焙烧温度的升高而减弱并分裂。红外吸收带向低频方向移动。SEM-EDAX结果表明:随样品焙烧温度的升高,结晶度下降,分子筛晶形变得不规则,晶面越来越粗糙,但结晶度的下降并非由于其中PO_4四面体的热分解所引起,而是由外部联结的T-O-T键的断裂,双环被破坏及骨架元素间的重排所引起。 相似文献
77.
This paper has analysed the major characteristics of long-term variation, of summermonsoon climate in South Asia since 1888. An abrupt enhancement of summer monsoon inthe 1920s and its synchronism with the global rapid warming have been detected by theMann-Kendall Rank Statistic test. Based on diagnostic analysis on the atmospheric circulationover the monsoon region and the thermal conditions of both ocean and land during theperiod of abrupt change, it is found that the warming over land was stronger and earlierthan that over the ocean, which would enhance the land-sea thermal contrast and thereforebe favorable to the development of monsoon low and the disturbance in the monsoon flow.This may be a direct factor for the abrupt enhancement of summer monsoon. 相似文献
78.
Yongsong Luo Xiaohong Xia Yonggang Zhang Jialin Li Zhijie Jia 《Journal of solid state chemistry》2007,180(6):1928-1933
Luminescence of the short multiwalled carbon nanotubes (MWNTs) conjugated with carboxylic acid groups has been studied. The results show that the carboxyl-functionalized short MWNTs could emit luminescence and the emission peak appears at 500 nm with a corresponding optimal excitation wavelength centering at 310 nm. When the short MWNTs are filtered through 0.15 μm polytetrafluoroethylene (PTFE) membrane, the ultrashort MWNTs are obtained from the filtrate. An interesting feature for the ultrashort MWNTs is that the emission intensity is strengthened and the peak is slightly blue shifted to 460 nm. This result indicates that the luminescence properties of MWNTs are strongly affected by the tube length. After chemical oxidization cutting, defects and carboxylic acid groups at the tube end and/or sidewall can be produced; the more shorten of MWNTs, the better dispersion and carboxylic passivation of the nanotubes, and the more intense luminescence emissions. The broad emissions are logically attributed to the trapping of excitation energy by defect sites in the carboxyl-functionalized nanotube structure. 相似文献
79.
Jana Mikulova Francois Gérard Danielle Mesnard Charles Kappenstein Daniel Duprez 《Journal of solid state chemistry》2006,179(8):2511-2520
CeO2 doped with praseodymium, neodymium and/or zirconium atoms were prepared by coprecipitation and by the sol-gel method. Structural properties were investigated by in situ XRD and Raman spectroscopy while oxygen storage capacity (OSC) was measured by transient CO oxidation. All the compounds, except pure Nd2O3, have a fluorite-type structure as well as a Raman band at 560 cm−1 characteristic of the oxygen vacancies involving non-stoichiometric oxides. The lattice parameter under hydrogen, being dependent on the temperature, revealed two reduction mechanisms: one at a low temperature at the surface and another at a high temperature in the bulk. Ce-Nd binary oxides show a strong tendency towards crystallite aggregation, which reduces accessibility to gases and OSC properties. Zirconium improves the thermal resistance to sintering of both Ce-Nd and Ce-Pr oxides. The Zr-Ce-Pr-O followed by Zr-Ce-Nd-O compounds displaying high oxygen mobility at a low temperature, appear to be very promising for practical applications such as OSC materials. 相似文献
80.
综述了三配位五价磷化合物的结构犊 征及其所具有的加成反应,络合反应,磷中心的亲电反应等化学性质。参考文献22篇。 相似文献