In this paper, we describe the formation of Au nanoparticle-graphene oxide (Au-GO) and -reduced GO (Au-rGO) composites by noncovalent attachment of Au nanoparticles premodified with ...2-mercaptopyridine to GO and rGO sheets, respectively, viaπ-π stacking and other molecular interactions. Compared with in situ reduction of HAuCl4 on the surface of graphene sheets that are widely used to prepare Au-GO composites, the approach developed by us offers well controlled size, size distribution, and morphology of the metal nanoparticles in the metal-GO nanohybrids. Moreover, we investigated surface enhanced Raman scattering (SERS) and catalysis properties of the Au-graphene composites. We have demonstrated that the Au-GO composites are superior SERS substrates to the Au NPs. Similarly, a comparative study on the catalytic activities of the Au, Au-GO, and Au-rGO composites in the reduction of o-nitroaniline to 1,2-benzenediamine by NaBH4 indicates that both Au-GO and Au-rGO composites exhibit significantly higher catalytic activities than the corresponding Au nanoparticles.
Recent advances in device-free wireless sensing (DFS) have shown that it may eventually evolve traditional wireless networks into smart networks which could sense surrounding target location and ...activity information without equipping the target with any devices. Despite its promising application prospects, one challenging problem to be solved is that the performance of the DFS system degrades significantly in complex scenarios, such as through-wall and non-line-of-sight (NLOS) scenarios. To alleviate this problem, this paper seeks to explore and exploit more informative features from not only the time domain and frequency domain, but also the spatial structural domain. We partition the time domain and frequency domain measurement matrices into basic structure blocks, adopt self-organizing map networks to cluster the blocks into a number of categories, so as to make it feasible to characterize the block distributions. We further adopt coherence histograms to characterize the distribution of the blocks by considering the spatial relationship between adjacent blocks. Thanks to the additional information provided by the spatial structural domain, extensive experimental results achieved in through-wall and NLOS scenarios confirm the outstanding performance of the proposed multi-domain features based DFS system.
Triaxial loading and unloading tests on marble specimens under different stress paths were conducted to investigate the characteristics of energy evolution in rock deformation process. Results show ...that tensile failure occurred in rock specimens under uniaxial compression, while shear failure dominated under triaxial loading and unloading. The energy storage limit of rock specimens under triaxial loading was higher than that under uniaxial compression or triaxial unloading. A nonlinear energy evolution model of rock was established based on the interaction mechanism of energy accumulation and energy dissipation. Results from the theoretical model are in good agreement with the test results. Since the evolution of energy was characterised by bifurcation and chaos, a strain value corresponding to the energy iterative growth factor at the first bifurcation of the energy equation was chosen as the initiation criterion for rock failure. The critical strain accounted for 77%, 72–76%, and 72–81% of the peak strain under uniaxial compression, triaxial loading, and unloading, respectively.
Van der Waals coupling is emerging as a powerful method to engineer physical properties of atomically thin two-dimensional materials. In coupled graphene-graphene and graphene-boron nitride layers, ...interesting physical phenomena ranging from Fermi velocity renormalization to Hofstadter's butterfly pattern have been demonstrated. Atomically thin transition metal dichalcogenides, another family of two-dimensional-layered semiconductors, can show distinct coupling phenomena. Here we demonstrate the evolution of interlayer coupling with twist angles in as-grown molybdenum disulfide bilayers. We find that the indirect bandgap size varies appreciably with the stacking configuration: it shows the largest redshift for AA- and AB-stacked bilayers, and a significantly smaller but constant redshift for all other twist angles. Our observations, together with ab initio calculations, reveal that this evolution of interlayer coupling originates from the repulsive steric effects that leads to different interlayer separations between the two molybdenum disulfide layers in different stacking configurations.
By functionalizing the privileged biphenyl-2-ylphosphine with a basic amino group at the rarely explored 3′ position, the derived gold(I) complex possesses orthogonally positioned “push” and “pull” ...forces, which enable for the first time soft propargylic deprotonation and permit the bridging of a difference of >26 pK a units (in DMSO) between a propargylic hydrogen and a protonated tertiary aniline. The application of this design led to efficient isomerization of alkynes into versatile 1,3-dienes with synthetically useful scope under mild reaction conditions.
Maleimides and succinimides are all vital scaffolds in biological fields and various natural products. Maleimide derivatives have been extensively used as coupling partners for various organic ...transformations, affording a broad array of important molecular architectures including succinimides. In the past decade, a variety of efficient chelation‐assisted strategies have been employed for the selective addition of C−H bonds to maleimides giving succinimides, which are also highly important building blocks in organic synthesis. This Review provides an overview of research progress relating to maleimides participated transition‐metal‐catalyzed group‐directed C−H alkylation from 2012 to 2021. Significant advances in this field were highlighted, diverse transition metal catalysts, organic substrates contained different directing groups, reaction mechanisms as well as synthetic applications are systematically discussed. In addition, the limitations and intractable issues need to be solved in the future are also pointed out.
This Review summarizes significant advances in directing‐group‐controlled transition‐metal‐catalyzed selective C(sp2)−H/C(sp3)−H alkylation with maleimides. Catalysts, substrates, directing groups, reaction mechanisms, synthetic applications as well as limitations and intractable issues of this field were systematically discussed.
Facile cycloisomerization of (2-ethynylphenyl)alkynes is proposed to be promoted synergistically by two molecules of BrettPhosAuNTf2, affording tricyclic indenes in mostly good yields. A gold ...vinylidene is most likely generated as one of the reaction intermediates on the basis of both mechanistic studies and theoretical calculations. Different from the well-known Rh, Ru, and W counterparts, this novel gold species is highly reactive and undergoes facile intramolecular C(sp3)–H insertions as well as O–H and N–H insertions. The formation step for the gold vinylidene is predicted theoretically to be complex with a bifurcated reaction pathway. A pyridine N-oxide acts as a weak base to facilitate the formation of an alkynylgold intermediate, and the bulky BrettPhos ligand in the gold catalyst likely plays a role in sterically steering the reaction toward formation of the gold vinylidene.
A low-profile planar Yagi-Uda antenna with exact endfire radiation and vertical polarization is presented in this paper. The concept is the combination of an aperture element and a novel vertical ...I-shaped resonator (VISR). The aperture acts as the driven antenna, which can be equivalent of a virtual magnetic dipole. The VISR array constructed with VISR unit cell is employed as a director or a reflector element depending on the resonant frequency of the unit cell, which consists of two identical rectangular metal conductors printed on both sides of a substrate and their electrical connection using via holes. Two prototype antennas are then designed, fabricated, and measured to test the validity of the operating principle. Antenna I with one director and one reflector achieves an endfire realized gain of 9.9-10.3 dBi and a front-to-back ratio (FBR) of more than 17.4 dB across 6.36-6.70 GHz. With four directors and one reflector, an endfire realized gain of 12.9-13.6 dBi and an FBR of more than 17.9 dB are accomplished by antenna II across 6.38-6.71 GHz. Moreover, a sensitivity analysis is implemented for the proposed antennas. Simulated results show that the standard PCB process is a reliable method for antenna fabrication.
The direct addition of in situ generated hydrazoic acid to alkynes is realized without solvent by using a gold catalyst derived from a recently designed remotely functionalized biaryl-2-ylphosphine ...ligand (i.e., WangPhos). With terminal alkynes, the additions are mostly realized with 0.1 mol% catalyst loadings and at 40 °C. With more challenging internal alkynes devoid of direct EWG substitution, the one-step transformation is realized for the first time with generally high efficiency at ambient temperature.
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