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31.
Hui Jin Yan-bing Hou Xian-guo Meng Feng Teng 《高分子科学》2006,(6):553-558
In this paper, photoexcitation processes in the bilayer devices based on inorganic materials and poly(N-vinylcarbazole) (PVK) were investigated. In order to clarify the roles of inorganic materials in photoconductive properties of bilayer devices, TiO2 and ZnS were chosen to combine with PVK. A model for generation of photocurrent (Iph) in single layer device of PVK was obtained. It is deduced that the recombination rate constant (Pcomb) and the ionization rate constant (y) ofexcitons should be considered as the most important factors for Iph. For inorganic materials (TiO2 or ZnS)/PVK bilayer devices, in reverse bias of-4 V, the photocurrent of 115 mA/cm^2 in the TiO2/PVK device was observed, but the photocurrent in the ZnS/PVK device was only 10 mA/cma under the illumination light of 340 nm and the light intensity of 14.2 mW/cm^2. The weaker photocurrent is attributed to the absorption of ZnS within UV region and the energy offset at the interface between PVK and ZnS, which impedes the transport of charge carriers. 相似文献
32.
Jihong Cheng 《Journal of solid state chemistry》2004,177(1):126-133
LaGaO3 perovskites doped with Sr or Ba at the La site and Mg at the Ga site were prepared by solid-state reaction or sol-gel method and characterized. Enthalpies of formation from constituent oxides at 298 K were determined by high-temperature oxide melt solution calorimetry. Energetic trends are discussed in terms of defect chemistry. As oxygen deficiency increases, formation enthalpies define three trends, LaGa1−yMgyO3−δ (LGM), La1−xSrxGa1−yMgyO3−δ (LSGM), and La1−xBaxGa1−yMgyO3−δ (LBGM). They become less exothermic with increasing doping, suggesting a dominant destabilization effect from oxygen vacancies. The endothermic enthalpy of vacancy formation is 275±37, 166±18 and 138±12 kJ/mol of VO·· for LGM, LBGM and LSGM, respectively. Tolerance factor and ion size mismatch also affect enthalpies. In terms of energetics, Sr is the best dopant for the La site and Mg for the Ga site, supporting earlier studies, including oxygen ion conductivity and computer modeling. 相似文献
33.
Sousa Pedrares A Teng W Ruhlandt-Senge K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(9):2019-2024
Novel magnesium pyridine-2-thiolates were prepared by using alkane elimination chemistry. The resulting complexes display a metal coordination environment composed of sulfur/nitrogen bonding from the intramolecularly stabilized mercaptopyridine ligand, in addition to coordination by the oxygen centers from two THF donors. The compounds are well-suited model compounds for the magnesium centers in Photosystem I, in which magnesium, situated in the central chlorophyll ligand, is bound to sulfur from a nearby methionine residue. All compounds were characterized by (1)H, (13)C NMR, and IR spectroscopy, in addition to Xray crystallography. 相似文献
34.
流动注射-结晶紫-磷钼杂多酸离子缔合体系光度法测定水中痕量正磷酸盐 总被引:2,自引:0,他引:2
在一定的酸度条件下,结晶紫与磷钼杂多酸离子缔合物的流动注射分光光度法可直接测定痕量磷.灵敏度高,重现性和选择性好.水中常见离子不干扰痕量磷的测定,工作曲线的线性范围为0~500μg·L~(-1)的磷,检出下限达1.0μg·L~(-1),以120h~(-1)采样频率,对各种天然水样进行测定,回收率为92.5%~105.0%,相对标准偏差为0.1%~6.7%. 相似文献
35.
Using ethylenediamine as a template, two one-dimensional (1-D) aluminophosphate compounds [AlP(2)O(8)H][NH(3)CH(2)CH(2)NH(3)] (1) and [AlP(2)O(8)][NH(3)CH(2)CH(2)NH(3)][NH(4)] (2) have been prepared from a gel system: 1.0:x:y:44 Al(i-PrO)(3)-H(3)PO(4)-en-EG (x = 3.0-9.0, y = 1.0-11.0). Compound 1 consists of edge-sharing four-membered ring (MR) chains, denoted as AlPO-ESC, and compound 2 consists of corner-sharing 4-MR chains, denoted as AlPO-CSC. The molar ratio of en:H(3)PO(4) in the starting gel has an important influence on the final product. If en:H(3)PO(4) > or = 1, AlPO-CSC is obtained, while if en:H(3)PO(4) < 1, AlPO-ESC is formed. These two chains can transform to each other upon addition of some extra amount of en or H(3)PO(4) to the reaction mixture in which AlPO-ESC or AlPO-CSC is crystallized. On the basis of XRD and (27)Al and (31)P MAS NMR analyses, a possible chain-to-chain transformation mechanism is proposed. The corner-sharing 4-MR chains of AlPO-CSC, as well as the edge-sharing 4-MR chains of AlPO-ESC can be assembled to 3-D open-framework compound NiAlP(2)O(8).C(2)N(2)H(9) through Ni(2+) cations. It is noted that AlPO-CSC remains in the structure of NiAlP(2)O(8).C(2)N(2)H(9). It is believed that AlPO-ESC might be first transformed to AlPO-CSC followed by the assembly to 3-D open-framework of NiAlP(2)O(8).C(2)N(2)H(9) through Ni(2+) cations. 相似文献
36.
氢分子在金属表面的解离吸附与氢原子在金属体相的扩散是个典型的表面过程.前者在甲烷化及合成氨等基础化工反应中起着关键作用;后者常常导致金属材料的脆化与断裂,但过渡金属及其合金是安全和优良的储氢材料.因此,研究氢分子在金属表面的解离吸附与氢原子在金属体相的扩散,是多相催化与金属物理广泛感兴趣的课题,具有重要的理论和应用价值.本文采用分子动力学方法初步探讨了二者之间的关联.分子催化动力学为从微观层次上研究上述课题提供了一种理论方法.本文采用经过我们改进的半经验LEPS方法,计算了氢分子在Pd(100)和(110)晶面的解离和氢原子在钯表面与体相扩散的相互作用位能面,并根据计算结果探讨了其微观机理. 相似文献
37.
The pervaporation and vapor permeation performance of symmetrical and asymmetrical polycarbonate membranes, prepared via a dry-phase inversion and wet-phase inversion methods, respectively, were studied by measuring the permeation rate and separation factor. It was found that the polymer concentration effect on the pervaporation performance for the symmetrical polycarbonate membrane was lower than that for the asymmetrical polycarbonate membrane. Compared with pervaporation, vapor permeation has a significantly increased separation factor with a decreased permeation rate for the symmetrical polycarbonate membrane. Water molecules preferentially dissolve into the symmetrical polycarbonate membrane and diffuse easily through the membrane. 相似文献
38.
An extended family of aryl-substituted alkaline earth metal silylamides M{N(2,4,6-Me3C6H2)(SiMe3)}donor(n) was prepared using alkane elimination (Mg), salt elimination (Ca, Sr, Ba), and direct metalation (Sr, Ba). Three different donors, THF, TMEDA (TMEDA = N,N,N',N'-tetramethylethylenediamine), and PMDTA (PMDTA = N,N,N',N',N'-pentamethyldiethylenetriamine) were employed to study their influence on the coordination chemistry of the target compounds, producing monomeric species with the composition M{N(2,4,6-Me3C6H2)(SiMe3)}2(THF)2 (M = Mg, Ca, Sr, Ba), M{N(2,4,6-Me3C6H2)(SiMe3)}2TMEDA (M = Ca, Ba), and M{N(2,4,6-Me3C6H2)(SiMe3)}2PMDTA (M = Sr, Ba). For the heavier metal analogues, varying degrees of agostic interactions are completing the coordination sphere of the metals. Compounds were characterized using IR and NMR spectroscopy in addition to X-ray crystallography. 相似文献
39.
Systematic Study of Ti‐Distribution in Titanosilicate *BEA Zeolites via Symmetry‐Adapted Enumeration
The high performance of titanosilicate zeolites in various industrial oxidation reactions is highly affected by the distribution of Ti atoms in their frameworks. Because of their structural complexity, previous theoretical studies mainly focus on the preferential location of single Ti atoms within the unit cells of titanosilicate zeolites. When multiple Ti atoms are required, conventional approaches consider only symmetrically related T sites to reduce the computation complexity. Such symmetry‐constrained approaches obviously overlooked many possible configurations. Herein, we conduct a systematic study on the distribution of two Ti atoms in the unit cell of titanosilicate zeolite *BEA . Different from conventional symmetry‐constrained approaches, we introduce two Ti atoms simultaneously without any constraint and adopt a symmetry‐adapted algorithm to enumerate all possible configurations for double‐Ti introduction. We generate a total of 273 distinct configurations and analyze the Ti‐distribution via Boltzmann statistics. We find that many of the configurations overlooked by conventional symmetry‐constrained approaches indeed exhibit more feasible energies, which may lead to different Ti‐distributions. Our study indicates the necessity of unconstrained introduction of Ti atoms when multiple‐Ti atoms are considered for calculations. 相似文献
40.