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排序方式: 共有823条查询结果,搜索用时 187 毫秒
811.
以粉末压片法制样,采用X射线荧光光谱(XRF)法测定钛铁矿中TFe、TiO2、SiO2、Al2O3、CaO、MgO的含量。对样品的矿物效应、样品粒度、分析谱线等条件进行优化。利用不同产地的质控样品制作工作曲线,验证矿物效应影响不大;通过样品粒度小于74 μm,很好地解决了颗粒粒度效应的影响。 精密度实验表明,待测组分的相对标准偏差均低于3.6%(RSD,n=10),能满足钛铁矿中各组分的测定要求。 相似文献
812.
Lithium reagents have long played important roles in synthetic chemistry. However, unsaturated organosilicon lithium reagents are few in number. Herein, we describe the first isolation of a 1,2-dilithiodisilene: [(boryl)SiLi]2 (2) was prepared in 73% yield by the reduction of (boryl)tribromosilane (1, boryl = (HCArN)2B, Ar = 2,6-iPr2C6H3) with lithium in Et2O. The salt elimination reaction of 2 with dihaloboranes RBX2 afforded disilaborirenes [(boryl)Si]2BR (3a–c), whereas the reaction with two equivalents of B-bromocatecholborane ((cat)BBr) yielded the first tetraboryldisilene [(boryl)(cat)BSi]2 (4). X-ray diffraction analysis and density functional theory calculations indicated that the disilene 2 and tetraboryldisilene 4 feature an almost planar geometry and disilaborirenes 3a–c are aromatic with a silicon–boron hybrid 2π-electron delocalized structure. The results indicate that 1,2-dilithiodisilene 2 is a powerful synthetic reagent for the construction of novel silicon multiply bonded species with unique electronic structures and that the boryl substituents have significant electronic effects on the structure of silicon multiple bonding.Dianionic disilyne: reduction of boryltribromosilane yielded the 1,2-dilithio-disilene 2, which is a powerful transfer reagent for the synthesis of a novel 2π aromatic system and the first tetraboryldisilene. 相似文献
813.
Tonghui Zhao Mengting Li Dongdong Xiao Xiaoju Yang Lulu An Zhiping Deng Tao Shen Mingxing Gong Yi Chen Hongfang Liu Ligang Feng Xuan Yang Li Li Deli Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(5):e202315148
Tracking the trajectory of hydrogen intermediates during hydrogen electro-catalysis is beneficial for designing synergetic multi-component catalysts with division of chemical labor. Herein, we demonstrate a novel dynamic lattice hydrogen (LH) migration mechanism that leads to two orders of magnitude increase in the alkaline hydrogen oxidation reaction (HOR) activity on Pd@Pt over pure Pd, even ≈31.8 times mass activity enhancement than commercial Pt. Specifically, the polarization-driven electrochemical hydrogenation process from Pd@Pt to PdHx@Pt by incorporating LH allows more surface vacancy Pt sites to increase the surface H coverage. The inverse dehydrogenation process makes PdHx as an H reservoir, providing LH migrates to the surface of Pt and participates in the HOR. Meanwhile, the formation of PdHx induces electronic effect, lowering the energy barrier of rate-determining Volmer step, thus resulting in the HOR kinetics on Pd@Pt being proportional to the LH concentration in the in situ formed PdHx@Pt. Moreover, this dynamic catalysis mechanism would open up the catalysts scope for hydrogen electro-catalysis. 相似文献
814.
Peng Wu Shuang Geng Xinyu Wang Xinglong Zhang Hongfeng Li Lulu Zhang Yu Shen Baoli Zha Prof. Suoying Zhang Prof. Fengwei Huo Prof. Weina Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(17):e202402969
The structure and properties of materials are determined by a diverse range of chemical bond formation and breaking mechanisms, which greatly motivates the development of selectively controlling the chemical bonds in order to achieve materials with specific characteristics. Here, an orientational intervening bond-breaking strategy is demonstrated for synthesizing ultrathin metal–organic framework (MOF) nanosheets through balancing the process of thermal decomposition and liquid nitrogen exfoliation. In such approach, proper thermal treatment can weaken the interlayer bond while maintaining the stability of the intralayer bond in the layered MOFs. And the following liquid nitrogen treatment results in significant deformation and stress in the layered MOFs’ structure due to the instant temperature drop and drastic expansion of liquid N2, leading to the curling, detachment, and separation of the MOF layers. The produced MOF nanosheets with five cycles of treatment are primarily composed of nanosheets that are less than 10 nm in thickness. The MOF nanosheets exhibit enhanced catalytic performance in oxygen evolution reactions owing to the ultrathin thickness without capping agents which provide improved charge transfer efficiency and dense exposed active sites. This strategy underscores the significance of orientational intervention in chemical bonds to engineer innovative materials. 相似文献
815.
816.
By considering the contribution of dynamic cue to auditory vertical localization,a method for virtual reproduction of surround sound in frontal space using four... 相似文献
817.
A photocatalyst- and metal-free radical tandem alkylation/cyclization between 1,6-dienes and redox-active esters has been developed, affording a series of N-aryl pyrrolidine-2-ones in moderate to good yields. The transformation is driven by the formation of an electron-donor-acceptor (EDA) complex and a subsequent single electron transfer (SET) process. This photocatalyst-free protocol features excellent regioselectivity, mild conditions and broad substrate scope, providing a facile access to 3-alkyl-3,4-dimethyl-1-phenylpyrrolidin-2-one. 相似文献
818.
Xinhong Xiong Hong Wang Lulu Xue Jiaxi Cui 《Angewandte Chemie (International ed. in English)》2023,62(47):e202306565
The growth of living systems is ubiquitous. Living organisms can continually update their sizes, shapes, and properties to meet various environmental challenges. Such a capability is also demonstrated by emerging self-growing materials that can incorporate externally provided compounds to grow as living organisms. In this Minireview, we summarize these materials in terms of six aspects. First, we discuss their essential characteristics, then describe the strategies for enabling crosslinked organic materials to self-grow from nutrient solutions containing polymerizable compounds. The developed examples are grouped into five categories based on their molecular mechanisms. We then explain the mechanism of mass transport within polymer networks during growth, which is critical for controlling the shape and morphology of the grown products. Afterwards, simulation models built to explain the interesting phenomena observed in self-growing materials are discussed. The development of self-growing materials is accompanied by various applications, including tuning bulk properties, creating textured surfaces, growth-induced self-healing, 4D printing, self-growing implants, actuation, self-growing structural coloration, and others. These examples are then summed up. Finally, we discuss the opportunities brought by self-growing materials and their facing challenges. 相似文献
819.
The adaptability of biological organisms to the environment is reflected in many aspects, especially in their camouflage of appearance. Inspired by biological camouflage strategies, a number of adaptive camouflage materials and devices have been developed to protect soldiers, vehicles, or equipment in the military. Today, the need for adaptive camouflage extends into people’s lives, whose privacy and information security need to be protected in the era of big data. Herein, a review is provided on the recent advancements of adaptive camouflage from the perspective of biological organisms and bio-inspired materials. Firstly, according to different biological mechanisms, we review the typical organisms that use pigmentary color, structural color, and morphological variation for adaptive camouflage, as well as those combine these strategies. Then, we provide an up-to-date review on recent developments in bio-inspired adaptive camouflage materials and devices with an emphasis on visible, infrared, and multispectral camouflage. At last, this review concludes the challenges and prospects for the future development of adaptive camouflage materials. It is noteworthy that there is never the best camouflage. To counter advanced detection techniques, it is necessary to unremittingly develop new materials and technologies to meet the increasing need for adaptive camouflage. 相似文献
820.
Lulu Shen Dr. Yin Zheng Zitong Lin Tianzhu Qin Prof. Dr. Zhongxing Huang Prof. Dr. Weiwei Zi 《Angewandte Chemie (International ed. in English)》2023,62(8):e202217051
2-Aminoallyl cations are versatile 1,3-dipoles that could potentially be used for diverse (3+n) cycloaddition reactions. Despite some preliminary studies, the asymmetric catalytic transformation of these species is still underdeveloped. We herein report a binuclear copper-catalyzed generation of 2-aminoallyl cations from ethynyl methylene cyclic carbamates and their enantioselective (3+2) cycloaddition reaction with indoles to construct chiral pyrroloindolines. This transformation features a novel C1,N-dipolar reactivity for 2-aminoallyl cations. 相似文献