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排序方式: 共有365条查询结果,搜索用时 31 毫秒
1.
Gangya Wei Dr. Yunxiang Li Dr. Xupo Liu Jinrui Huang Mengran Liu Dr. Deyan Luan Prof. Shuyan Gao Prof. Xiong Wen Lou 《Angewandte Chemie (International ed. in English)》2023,62(47):e202313914
Precise manipulation of the coordination environment of single-atom catalysts (SACs), particularly the simultaneous engineering of multiple coordination shells, is crucial to maximize their catalytic performance but remains challenging. Herein, we present a general two-step strategy to fabricate a series of hollow carbon-based SACs featuring asymmetric Zn−N2O2 moieties simultaneously modulated with S atoms in higher coordination shells of Zn centers (n≥2; designated as Zn−N2O2−S). Systematic analyses demonstrate that the synergetic effects between the N2O2 species in the first coordination shell and the S atoms in higher coordination shells lead to robust discrete Zn sites with the optimal electronic structure for selective O2 reduction to H2O2. Remarkably, the Zn−N2O2 moiety with S atoms in the second coordination shell possesses a nearly ideal Gibbs free energy for the key OOH* intermediate, which favors the formation and desorption of OOH* on Zn sites for H2O2 generation. Consequently, the Zn−N2O2−S SAC exhibits impressive electrochemical H2O2 production performance with high selectivity of 96 %. Even at a high current density of 80 mA cm−2 in the flow cell, it shows a high H2O2 production rate of 6.924 mol gcat−1 h−1 with an average Faradaic efficiency of 93.1 %, and excellent durability over 65 h. 相似文献
2.
Rasitha Manha Veedu Niklas Niemeyer Dr. Nils Bäumer Dr. Krishnan Kartha Kalathil Prof. Dr. Johannes Neugebauer Prof. Dr. Gustavo Fernández 《Angewandte Chemie (International ed. in English)》2023,62(49):e202314211
The functionalization of π-conjugated scaffolds with sterically demanding substituents is a widely used tactic to suppress cofacial (H-type) stacking interactions, which may even inhibit self-assembly. Contrary to expectations, we demonstrate herein that increasing steric effects can result in an enhanced thermodynamic stability of H-type supramolecular polymers. In our approach, we have investigated two boron dipyrromethene (BODIPY) dyes with bulky phenyl ( 2 ) and mesityl ( 3 ) meso-substituents and compared their self-assembly in nonpolar media with that of a parent meso-methyl BODIPY 1 lacking bulky groups. While the enhanced steric demand induces pathway complexity, the superior thermodynamic stability of the H-type pathways can be rationalized in terms of additional enthalpic gain arising from intermolecular C−H⋅⋅⋅F−B interactions of the orthogonally arranged aromatic substituents, which overrule their inherent steric demand. Our findings underline the importance of balancing competing non-covalent interactions in self-assembly. 相似文献
3.
In the paper results of the investigation of the influence of electric properties of the environment surrounding LiNbO3 crystals on photorefractive effect induced in these crystals by Gaussian Ar+ laser beam with various intensities are presented. We show spatial and temporal dependences of changes of the refractive index obtained experimentally in LiNbO3: Fe and LiNbO3: Fe:Mn samples surrounded by media with different electric conductivities and different permittivities (water, air, water solution of CaCl2). The space and time dependences of the refractive index changes induced by the Ar+ laser beam are observed by means of the Mach–Zehnder interferometer using light from HeNe laser. The experimentally obtained results are in a good agreement with those following from numerical calculations using the manifold mirroring method. The agreement between calculated and experimental results indicates that the polarization charge at the photorefractive crystal/surrounding medium boundary significantly influences the photorefractive process in the crystal. The experimentally observed slow spontaneous decrease of the refractive index change in a sample placed into a slightly conducting medium (air) after switching off the beam also indicates that the polarization charge in the sample's surroundings affects the photorefraction. 相似文献
4.
Michael Esseling Annamaria Zaltron Wolfgang Horn Cornelia Denz 《Laser \u0026amp; Photonics Reviews》2015,9(1):98-104
This contribution presents an optofluidic droplet router which is able to route and steer microdroplets using optically induced forces created solely by the bulk photovoltaic effect on a nonlinear substrate. The combination of microfluidic tools with the properties of a photorefractive crystal allows for the generation of dielectrophoretic forces that can be either repulsive, leading to virtual barriers, or attractive, creating virtual rails. The sign of these forces is solely determined by the electrical properties of the liquid medium under investigation. Moreover, the induced structures on the bottom of the microfluidic channel are optically reconfigurable, so that the same device can easily be adopted for different purposes. Appropriate droplet‐generating devices are fabricated by UV illumination of SU‐8 and polydimethylsiloxane replica molding of the master structures. The bottom of the channels is formed by an iron‐doped lithium niobate crystal, whose internal electric fields are induced by structured illumination patterns and exert dielectrophoretic forces on droplets in the microfluidic section.
5.
For a nonlinear medium, a given incident laser beam may produce different transmitted light waves. This phenomenon (the so-called optical bistability) corresponds to multiple solutions of the boundary value problems of the nonlinear Helmholtz equation. Optical bistability can be useful in the design of optical switches. Devices that display this behavior could potentially play a major role in the development of optical communication systems and computing. In this article we present experimental results concerning the optical bistability in photorefractive BaTiO3:Fe crystal. Two laser beams were used to interact with the photorefractive crystal which resulted in the bistability of the intensity of transmitted wave. This was achieved without the application of any optical resonator. High contrast optical bistability is found experimentally in the pump-ratio dependence of the output intensity. 相似文献
6.
Separate spatial soliton pairs in a biased series centrosymmetric photorefractive crystal circuit 总被引:1,自引:0,他引:1
It is shown theoretically that three types of separate soliton pairs: bright-bright, bright-dark, and dark-dark, can be established in a biased series circuit consisting of two centrosymmetric photorefractive crystals and the two solitons in a separate soliton pair can affect each other by the light-induced current. The effects of the intensities of soliton beams and background lights on the normalized profiles of solitons are discussed. 相似文献
7.
An optical technique for slope detection by using as storing medium a photorefractive BSO crystal is proposed. The technique relays in that a local tilt produced in a diffusing reflective surface can be mapped as a speckle transversal shifting in a plane perpendicular to the optical axis. The volume nature of the storing medium is quite adequate to highlight the speckle volume nature and its associated properties. Experimental results obtained by using a rubber vibrating membrane are presented. 相似文献
8.
In this work, the improvement of the dynamic range of a micro displacement sensor based on fiber specklegrams holographically stored in a photorefractive BSO (Bi12SiO20) crystal is reported. In our experimental setup, a plastic optical fiber (POF) was used to generate a subjective speckle pattern that was recorded in the crystal using a two-wave mixing arrangement. The speckle size was controlled by modifying the diameter of a pupil aperture adjacent to a lens producing the image of the speckle. Fringe patterns were obtained at the output of the system by producing micro displacements of the fiber output end. An increase in the visibility of the fringe patterns was appreciated when the pupil aperture diameter decreased even without controlling the average modulation of the intensity of the light pattern, i.e. when the speckle length increased and the average light modulation simultaneously decreased. This behavior allowed recovering the autocorrelation functions of fringe patterns associated with displacements that initially led to decorrelation, and therefore, significantly to improve the dynamic range of the metrological system. To the best of our knowledge this is the first report about the influence of speckle size on the dynamic range of fiber specklegrams sensors recorded on photorefractive materials. 相似文献
9.
We investigated the face-stabilized Open-Hole Compression (OHC) test method for evaluating the effects of fiber waviness on the compression strength of continuous carbon fiber reinforced polymer composites. Temporal evaluations of the load-deformation response, acoustic emissions and optical microscopy are used to understand the failure modes and damage progression in the OHC specimen. The failure modes observed are structurally correlated to matrix failure and kink zone formation leading to fiber fracture. The results show how the resin pocket plays a more critical role than the layup in influencing the initiation of damage in the composite specimens. 相似文献
10.
Jeong Ah Chang 《Journal of solid state chemistry》2009,182(4):749-756
Nanosized anatase and rutile TiO2 having different shape, phase and size have been prepared from aqueous solutions of peroxo titanium complex starting from titanium(IV) isopropoxide (TTIP), acetic acid and hydrogen peroxide (H2O2) in water/isopropanol media by a facile sol-gel process. The TiO2 nanocrystals are characterized by powder X-ray diffraction (XRD), Raman spectroscopy, FT-IR spectroscopy, TEM, high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) techniques. The influence of pH and the sequence of addition of reaction contents on the phase and morphology of TiO2 are studied. The reasons for the observation of only anatase and/or mixture of anatase and rutile are given. 相似文献