Yukihide Shiraishi

Frequency modulation response of a liquid-crystal electro-optic device doped with nanoparticles

Palladium nanoparticles covered with liquid-crystal molecules were prepared by UV irradiation of an alcohol solution of palladium(II) acetate in the presence of liquid-crystal molecules. The prepared Pd nanoparticles have an average diameter of 2.5 nm. A twisted nematic (TN) liquid-crystal device (LCD) was fabricated by doping with Pd nanoparticles covered with another kind of nematic liquid-crystal molecules. In this device the sign of the dielectric anisotropy (Δe) of the liquid-crystal molecules, which cover Pd nanoparticles, is opposite to that of nematic liquid-crystal molecules, which work as the host of the device (Δe>0). The TN-LCD cell fabricated in this research exhibits a frequency modulation response to an applied alternative voltage wave form.

Novel Hybrid Organic Thermoelectric Materials:Three‐Component Hybrid Films Consisting of a Nanoparticle Polymer Complex, Carbon Nanotubes, and Vinyl Polymer

A novel class of hybrid organic thermoelectric materials is demonstrated for the first time for constructing flexible thermoelectric devices on polyimide substrates with high output power by using nanotechnology instead of conducting polymers such as poly(3,4-ethylenedioxythiophene). The hybrid organic thermoelectric materials are composed of nanoparticles of a polymer complex, carbon nanotubes, and poly(vinyl chloride), and show high performance (dimensionless thermoelectric figure-of-merit, ZT ≈ 0.3, based on the thermal conductivity through the film).

Fast Switching of Frequency Modulation Twisted Nematic Liquid Crystal Display Fabricated by Doping Nanoparticles and Its Mechanism

The electrooptic characteristics of a twisted nematic (TN) liquid crystal display (LCD) fabricated by doping Ag nanoparticles protected with NLC, 5CB (K-15, Merck) molecules have been investigated, and it is shown that the device exhibits a unique electrooptic response characteristic that is sensitive to the high-frequency components of the operating voltage together with the conventional root-mean-square voltage response. We call this device frequency modulation (FM) TN-LCD. The FM-TN-LCD is switched by switching the frequency of the operating voltage while its amplitude is kept unchanged. As an example, the frequency switched from 20 Hz to 500 Hz or 50 Hz to 2 kHz, and the switching is performed with the time constant of 21 ms for the rising process and 3 ms for the falling process. This device shows a peculiar response to a burst AC square wave, where the decay time is reduced by several times compared to that of an undoped TN-LCD. The mechanism of the FM-TN-LCD is investigated through the study of its dielectric properties.

Electrochemical synthesis of gold nanoparticles decorated flower-like graphene for high sensitivity detection of nitrite

In this paper, the spherical Au nanoparticles and 3D flower-like structure graphene were successively deposited on glassy carbon electrode (GCE) (Au/f-GE/GCE) via a facile and two-step electrodeposition method for the detection of nitrite ions (NaNO2). The morphology and composition elements were confirmed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction measurements (XRD). Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to evaluate the electrochemical behaviors of NaNO2 on the as-prepared electrode. Compared to f-GE/GCE and Au/GCE, Au/f-GE/GCE showed a sharp and obvious oxidation peak at 0.78V. The oxidation peak current of NaNO2 was linearly proportional to its concentration in the range from 0.125 to 20375.98μM, with a detection limit of 0.01μM (at S/N=3). Furthermore, the experiment results also showed that the as-prepared electrode exhibited excellent reproducibility and long-term stability, as well as good recovery when applied to the determination of NaNO2 in pickled pork samples.

Frequency modulation response of a tunable birefringent mode nematic liquid crystal electrooptic device fabricated by doping nanoparticles of Pd covered with liquid-crystal molecules

We fabricated a tunable birefringent (TB) mode nematic liquid-crystal (NLC) electrooptic device using NLC-K15 (Merck) as a host NLC (called NLC-1), where the cell is doped with Pd nanoparticles covered with NLC (NLC-2) molecules, having a cyano group such as 5CB (Merck) with positive dielectric anisotropy (Δe>0) or CCN-47 (Merck) with negative Δe (Δe<0). The diameter of the core Pd particle is 2.5 nm and the concentration of nanoparticles is 1 wt%. The TB mode LCD cell fabricated in this way exhibits a remarkable frequency modulation response below 100 Hz of the driving voltage waveform. It is considered that the frequency modulation (FM) response of the TB-NLCD may be attributed to Maxwell-Wagner type interfacial polarization between the host NLC medium and doped nanoparticles.

Self-supported porous 2D AuCu triangular nanoprisms as model electrocatalysts for ethylene glycol and glycerol oxidation

Shape-controlled synthesis of self-supported metallic nanocrystals with abundant active surface areas is of vital importance for the design and fabrication of novel outstandingly excellent electrocatalysts. Motivated by this, we herein report our research in the synthesis of self-supported porous 2D AuCu triangular nanoprisms via a facile wet-chemical method. Owing to the attractive 2D triangular structure, bifunctional and electronic effects between Au and Cu, such unique Au1Cu1 nanoprisms exhibited extremely high catalytic activities towards ethylene glycol and glycerol electrooxidation with mass activities of 2873 and 2263 mA mgAu−1, which are 3.0 and 3.9-fold enhancements over those of pure Au (958 and 573 mA mgAu−1), respectively. We trust this strategy may be extended to the syntheses of other multimetallic nanocatalysts with such fascinating nanostructures and the as-obtained porous triangular nanoprisms can be well applied to serve as highly desirable anode catalysts for electrooxidation of ethylene glycol and glycerol.

Facile fabrication of novel PdRu nanoflowers as highly active catalysts for the electrooxidation of methanol

The shape-controlled synthesis of binary Pd-based nanocrystals bounded with abundant surface active areas and tunable atomic ratio have been of great significance in the fabrication and modification of outstandingly excellent electrocatalysts. To embody the superiority of high surface area in enhancing electrocatalysis well, the superior electrocatalyst should be supposed to combine both the morphology advantages and the synergistic effect between metals. We herein report our significant advances in engineering the unique binary PdRu nanoflowers with highly exposed active sites and tunable compositions. Owing to the bifuntional effect and electronic effect between Pd and Ru, as well as the unique flower-like structure, such special PdRu nanoflower exhibit outstandingly excellent catalytic activity towards methanol electrooxidation with the mass activity of 1280mAmg-1, 7.01 and 4.92-fold enhancement than that of pure Pd and commercial Pd/C. Our efforts in this work may open a new way for enhancing the catalytic activity by constructing the catalysts with desirable shape and maximizing the active surface areas.

Dielectric Properties of Frequency Modulation Twisted Nematic LCDs Doped with Palladium (Pd) Nanoparticles

Twisted nematic liquid crystal display (TN-LCD) devices, composed of nematic liquid crystal (NLC), doped with palladium (Pd) nanoparticles, which are protected with the same NLC molecules of 5CB (Merck, K-15), show electrooptic characteristics that are featured by a frequency modulation and fast response. This device is called FM-TN-LCD. In this paper, we report that the frequency range in the FM-TN-LCD spreading from tens Hz to an upper limit 1 kHz, depending on the concentration of nanoparticles, correlates with that of the dielectric dispersion of the sample cell, which is expressed analytically by the Maxwell–Wagner theory on the heterogeneous dielectric medium, where the dielectric relaxation frequency, and thus the dielectric relaxation time, are primarily governed by the electrical conductivity of the doped nanoparticles of Pd and their concentrations.

Dielectric Properties of Frequency Modulation Twisted Nematic LCDs Doped with Silver Nanoparticles

Twisted nematic liquid crystal display (TN-LCD) devices, composed of nematic liquid crystal (NLC), doped with silver (Ag) nanoparticles, which are protected with the same NLC molecules of 5CB (Merck, K-15), show electrooptic characteristics that are featured by a frequency modulation and fast response. This device is called FM-TN-LCD. In this paper, we report that the frequency range in the FM-TN-LCD spreading from 40 Hz to an upper limit 2 kHz correlates with that of the dielectric dispersion of the sample cell, which is expressed analytically by the Maxwell–Wagner theory on the heterogeneous dielectric medium, where the dielectric relaxation frequency, and thus the dielectric relaxation time, are primarily governed by the electrical conductivity of the doped Ag nanoparticles.

Preparation and Catalysis of Inverted Core/Shell Structured Pd/Au Bimetallic Nanoparticles

Reduction of two different precious metal ions by refluxing in ethanol/water in the presence of poly(N-vinyl-2-pyrrolidone) (PVP) gave a colloidal dispersion of core/shell structured bimetallic nanoparticles. In the case of Pd and Au ions, for example, the colloidal dispersions of bimetallic nanoparticles with a Au core/Pd shell structure are produced. In contrast, it is difficult to synthesize bimetallic nanoparticles with the inverted core/shell (in this case, Pd core/Au shell) structure. Here the sacrificial hydrogen strategy has been used to construct the inverted core/shell structure, where the colloidal dispersions of Pd cores are treated with hydrogen and then the solution of the second element, Au ions, is slowly added to the dispersions. This novel method, developed by us, gave the inverted core/shell structured bimetallic nanoparticles. The Pd core/Au shell structure has been confirmed by FT-IR spectra of adsorbed carbon monoxide. The hydrogenation of methyl acrylate catalyzed by the nanoparticles before and after heat treatment was investigated as well.