A general synthesis route to a family of single-crystal chromate nanorods/nanobelts has been established. The effects of pH and surfactant on phase and morphology of these microcrystalline materials have been investigated. The physical properties of the as-synthesized chromate nanocrystals such as dielectric, electrochemical, UV-vis absorbance, and photoluminescent properties have also been studied. The present general synthesis of various low-dimensional chromate nanomaterials provides useful information on the possible synthesis of other microcrystalline transition metal oxysalts.
Palladium (Pd) nanoparticles are of particular interest to various fundamental studies and emerging areas of technology. The properties of Pd nanoparticles have a strong dependence on particle size. Nevertheless, it has been challenging to synthesize uniform Pd nanoparticles with controllable sizes and in relatively large quantities. Herein, we demonstrate a simple yet robust one-pot synthesis for the preparation of single-crystal Pd nanoparticles with controllable sizes in the range 2–14 nm. The synthesis is simply performed by mixing polyvinylpyrrolidone (PVP), Na2PdCl4, and ethylene glycol in a glass vial that is placed in an oil bath with stirring. The sizes could be conveniently and tightly controlled by adjusting the amount of PVP or Na2PdCl4/PVP. The final products are highly uniform in terms of size and shape. Notably, the strategy of size control was successfully extended to Pt and Rh nanoparticles. The synthesis could be scaled up to allow for the production of gram-level quantities of Pd nanoparticles in a short period of time. The uniform Pd nanoparticles with controllable sizes are believed to find important use in different areas, such as fundamental nanoresearch, catalysis, and biomedicine.
A sodium alginate (SA) cation layer was modified by cobalt octocarboxyphthalocyanine (CoPc(COOH)8) to improve its ion exchange capacity and to promote water splitting at the interlayer. The CoPc(COOH)8-SA and chitosan (CS) were then modified using Fe(superscript 3+) and glutaraldehyde as linking reagents to prepare CoPc(COOH)8-SA/mCS bipolar membranes(BPMs). FT-IR spectra and SEM were used to characterize CoPc(COOH)8-SA/mCS BPMs. Experimental results showed that the ion exchange capacity and hydrogen ion transmigration rate of the CoPc(COOH)8-SA cation exchange membrane had increased. By comparison to the mSA/mCS BPM that was modified by Fe(superscript 3+) or ferrocene, the AC impedance, IR drop and the swelling degree of the CoPc(COOH)8-SA/mCS BPMs all decreased. The IR drop of the CoPc(COOH)8-SA/mCS BPM was only 0.7 V at a higher current density of 105 mA•cm^(-2).
We report a two-colored plasmonic antenna which can control the directivity of the excitation and emission light independently and simultaneously. By carefully tuning the phase difference of the constituting elements of the antenna, unidirectional fluorescence emission and laser light scattering can be obtained. In particular, the direction of the maximum emission and minimum scattering can be tailored in the same direction resulting improvement of signal to noise ratio in single molecule experiment. A two-dipole model is applied to describe the phenomena. The radiation and scattering pattern can be further tuned by varying the antenna structure.
A long-range, high-precision, and compact transverse displacement metrology method is of crucial importance in many research areas. Recent schemes using optical antennas are limited in efficiency and the range of measurement due to the small size of the antenna. Here, we demonstrated the first prototype polarization-encoded metasurface for ultrasensitive long-range transverse displacement metrology. The transverse displacement of the metasurface is encoded into the polarization direction of the outgoing light via the Pancharatnam-Berry phase, which can be read out directly according to the Malus law. We experimentally demonstrate nanometer displacement resolution with the uncertainty on the order of 100 picometers for a large measurement range of 200 micrometers with the total area of the metasurface being within 900 micrometers by 900 micrometers. The measurement range can be extended further using a larger metasurface. Our work opens new avenues of applying metasurfaces in the field of ultrasensitive optical transverse displacement metrology.
Abstract The development of chiral nanostructures‐based supramolecular catalysts with satisfied enantioselectivity remains a significantly more challenging task. Herein, the synthesis and self‐assembly of various amino acid amphiphiles as chiral supramolecular catalysts after metal ion coordination is reported and systematically investigate their enantioselectivity in asymmetric Diels–Alder reactions. In particular, the self‐assembly of l / d ‐phenylglycine‐based amphiphiles ( l / d ‐PhgC 16 ) and Cu(II) into chiral supramolecular catalysts in the methanol/water solution mixture is described, which features the interesting M/P nanohelices (diameter ≈8 nm) and mostly well‐aligned M/P nanoribbons (NRs). The M / P supramolecular catalysts show both high but inverse enantioselectivity (>90% ee ) in Diels–Alder reactions, while their monomeric counterparts display nearly racemic products. Analysis of the catalytic results suggests the outstanding enantioselectivities are closely related to the specific stereochemical microenvironment provided by the arrangement of the amphiphiles in the supramolecular assembly. Based on the experimental evidence of chirality transfer from supramolecular nanohelices to coordinated Cu(II) and substrate aza‐chalcone and the molecular dynamics simulations, the enantioselective catalytic mechanisms are proposed. Moreover, the relationships between molecular structures of amino acid amphiphiles (the hydrophilic head group and hydrophobic alkyl chain length) in supramolecular catalysts and enantioselectivity in Diels–Alder reactions are elaborated.
The noise reduction mechanism of perforated elastic pavement was analyzed from three aspects such as sound-absorbing porous,resonance absorbing porous and damped noise reduction,and noise evaluation methods of perforated elastic pavement were summarized,this pavement type was analyzed from acoustics aspect,and pointed out that perforated elastic pavement has good noise reduction effect.
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