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排序方式: 共有119条查询结果,搜索用时 15 毫秒
111.
Xiaoxia Li Ni Zhen Chengpeng Liu Di Zhang Jing Dong Yingnan Chi Changwen Hu 《Molecules (Basel, Switzerland)》2022,27(9)
During the controllable synthesis of two vanadium-containing Keggin-type polyoxoniobates (PONbs), [Ni(en)2]5[PNb12O40(VO)5](OH)5·18H2O (1) and [Ni(en)3]5[PNb12O40(VO)2]∙17H2O (2, en = ethylenediamine) are realized by changing the vanadium source and hydrothermal temperature. Compounds 1 and 2 have been thoroughly characterized by single-crystal X-ray diffraction analysis, FT-IR spectra, X-ray photoelectron spectrum (XPS), powder X-ray diffraction (PXRD), etc. Compound 1 contains a penta-capped Keggin-type polyoxoniobate {PNb12O40(VO)5}, which is connected by adjacent [Ni(en)2]2+ units into a three-dimensional (3D) organic-inorganic framework, representing the first nickel complexes connected vanadoniobate-based 3D material. Compound 2 is a discrete di-capped Keggin-type polyoxoniobate {PNb12O40(VO)2} with [Ni(en)3]2+ units as counter cations. Compounds 1 and 2 have poor solubility in common solvents and can keep stable in the pH range of 4 to 14. Notably, both 1 and 2 as electrode materials are active for the selective oxidation of benzyl alcohol to benzaldehyde. Under ambient conditions without adding an alkaline additive, compound 1 as a noble metal free electrocatalyst can achieve 92% conversion of benzyl alcohol, giving a Faraday efficiency of 93%; comparatively, 2 converted 79% of the substrate with a Faraday efficiency of 84%. The control experiments indicate that both the alkaline polyoxoniobate cluster and the capped vanadium atoms play an important role during the electrocatalytic oxidation process. 相似文献
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114.
Xiang-Yu GUO Xue-Mei HUANG Jun-Feng ZHAI Hua BAI Xiao-Xu LI Xiao-Xiao MA Qiang MA 《分析化学》2019,47(3):335-346
The development and applications of ambient ionization and miniature mass spectrometry are current research focus in chemical measurement. The analytical technology based on the combination of ambient ionization and miniature mass spectrometry can bypass chromatographic separation and eliminate or simplify sample pretreatment process. The protocol can reverse the labor-intensive and time-consuming drawbacks of traditional analytical methodologies, and realize rapid, on-site analysis with high sensitivity and high throughput. In this paper, the research progress and applications of ambient ionization and miniature mass spectrometry in the fields of food safety, consumer product safety, public security, life sciences and environmental monitoring, are reviewed, and future trends and prospects are discussed, which may provide technical guidance for the researchers engaged in relevant fields. 相似文献
115.
《Tetrahedron letters》1987,28(26):2963-2966
Organocuprate addition reactions on methyl-bis(trimethylsilyl)aminomethyl-propiolate lead to the formation of a Z-vinyl cuprate with a high stereoselectivity. Upon reaction of acid chloride, pyrroles are formed by a spontaneous intramolecular cyclisation of the intermediate Z-silylamino enone. Various functional substituted pyrroles can be obtained in one step by this route. 相似文献
116.
《结构化学》2020,39(9):1585-1593
Mineral medicine, especially those containing heavy metals, is one of the characteristics of traditional Chinese medicine. A famous mineral medicine, realgar, containing heavy metal arsenic with a chemical formula of As_4S_4, has the function of detoxification, killing bacteria and viruses, and eliminating dampness and phlegm. Different As_4S_4 isomers are likely to have different drug effects and pharmacological actions. Therefore, it is of great scientific significance to find more stable As_4S_4 isomers. In view of this, ab initio molecular orbital theory and density functional theory(DFT) have been used to study ten isomers of As_4S_4 at the B3LYP/6-31 G*, B3LYP/6-311+G*, B3LYP/6-311+G(3 df, 2 p) and MP2/(6-311+G*, LanL2 MB) levels of theory. In addition to the two isomers having been studied previously, eight new isomers were investigated in the present paper. All the ten As_4S_4 isomers were proved to be true local minima on their potential energy surfaces. The calculated NICS values and molecular orbital analyses showed that, the D_(2d) symmetric As_4S_4, isomer 1, may be s-aromatic. The study proves that ten As_4S_4 isomers are stable thermodynamically, and are highly desirable for the future theoretical study of realgar. 相似文献
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118.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1984,40(10):929-938
The gas phase i.r. spectrum of CF3I has been investigated in the ν2, ν3, 2ν3 and ν2 + ν3 region with a resolution of 0.04 cm−1. Rotational J clusters have been resolved, and several vibrational and rovibrational parameters of ν2, 743.364(8) cm−1 and ν3, 286.303(3) cm−1, have been determined by polynomial methods and by band contour simulation. 相似文献
119.
《Communications in Nonlinear Science & Numerical Simulation》2010,15(5):1408-1418
This paper aims to present a biophysical understanding of the agricultural ecological engineering by emergy analysis for a farm biogas project in China as a representative case. Accounting for the resource inputs into and accumulation within the project, as well as the outputs to the social system, emergy analysis provides an empirical study in the biophysical dimension of the agricultural ecological engineering. Economic benefits and ecological economic benefits of the farm biogas project indicated by market value and emergy monetary value are discussed, respectively. Relative emergy-based indices such as renewability (R%), emergy yield ratio (EYR), environmental load ratio (ELR) and environmental sustainability index (ESI) are calculated to evaluate the environmental load and local sustainability of the concerned biogas project. The results show that the farm biogas project has more reliance on the local renewable resources input, less environmental pressure and higher sustainability compared with other typical agricultural systems. In addition, holistic evaluation and its policy implications for better operation and management of the biogas project are presented. 相似文献