Helically aligned fused carbon hollow nanospheres with chiral discrimination ability.

While the functions of carbon materials with precisely controlled nanostructures have been reported in many studies, their chiral discriminating abilities have not been reported yet. Herein, chiral discrimination is achieved using helical carbon materials devoid of chiral attachments. A Fe3O4 nanoparticle template with ethyl cellulose (carbon source) is self-assembled on dispersed multiwalled carbon nanotubes (MWCNTs) fixed in a lamellar structure, with helical nanoparticle alignment induced by the addition of a binaphthyl derivative. Carbonization followed by template removal produces helically aligned fused carbon hollow nanospheres (CHNSs) with no chiral molecules left. Helicity is confirmed using vacuum-ultraviolet circular dichroism spectroscopy. Chiral discrimination, as revealed by the electrochemical reactions of binaphthol and a chiral ferrocene derivative in aqueous and nonaqueous electrolytes, respectively, is attributable to the chiral space formed between the CHNS and MWCNT surfaces.

Oriented growth of stacking α-cobalt hydroxide salt continuous films and their topotactic-like transformation to oriented mesoporous films of Co3O4 and CoO.

Mesoporous metal oxide films composed of nanocrystal assemblies with an aligned crystallographic orientation are key nanostructures for efficient interfacial reactions; however, the development of a simple and versatile method for their formation on substrates still constitutes a challenge. Here we report the template-free centimetre-scale formation of novel cobalt oxide films of Co3O4 and CoO with a [111]-oriented mesoporous structure starting from stacking cobalt hydroxide continuous films. The cobalt hydroxide precursor is formed electrochemically on conductive substrates from a Co(NO3)2 aqueous solution at room temperature. A thorough characterization by means of scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis-NIR spectroscopy, IR spectroscopy and Raman spectroscopy analyses reveals that the precursor film is an α-type layered cobalt hydroxide salt (α-Co-LHS) containing interlayer nitrate and hydrated water, i.e., α-Co(OH) x (NO3) y ·nH2O, with a [001]-oriented stacking film structure. Heat treatment of the [001]-α-Co-LHS films using different conditions, i.e., under air at 550 °C or under vacuum at 500 °C, results in the selective formation of Co3O4 or CoO mesoporous films, respectively. A plausible explanation for the observed centimetre-scale topotactic-like transformation from α-Co-LHS[001] to Co3O4[111] or CoO[111] is given according to the atomic framework similarity between the hydroxide precursor and the final oxides.

High-Resolution Mapping of Local Photoluminescence Properties in CuO/Cu2O Semiconductor Bi-Layers by Using Synchrotron Radiation.

The quality of a semiconductor, which strongly affects its performance, can be estimated by its photoluminescence, which closely relates to the defect and impurity energy levels. In light of this, it is necessary to have a measurement method for photoluminescence properties with spatial resolution at the sub-micron or nanoscale. In this study, a mapping method for local photoluminescence properties was developed using a focused synchrotron radiation X-ray beam to evaluate localized photoluminescence in bi-layered semiconductors. CuO/Cu2O/ZnO semiconductors were prepared on F:SnO2/soda-lime glass substrates by means of electrodeposition. The synchrotron radiation experiment was conducted at the beamline 20XU in the Japanese synchrotron radiation facility, SPring-8. By mounting the high-sensitivity spectrum analyzer near the edge of the CuO/Cu2O/ZnO devices, luminescence maps of the semiconductor were obtained with unit sizes of 0.3 µm × 0.3 µm. The devices were scanned in 2D. Light emission 2D maps were created by classifying the obtained spectra based on emission energy already reported by M. Izaki, et al. Band-like structures corresponding to the stacking layers of CuO/Cu2O/ZnO were visualized. The intensities of emissions at different energies at each position can be associated with localized photovoltaic properties. This result suggests the validity of the method for investigation of localized photoluminescence related to the semiconductor quality.

Electrochemical Growth of Mg(OH) x Layered Films Stacked Parallel to the Substrates and Their Thermal Conversion to (111)-Oriented Nanoporous MgO Films.

Stacking layered metal hydroxide films parallel to a substrate is challenging. Here, we demonstrate a simple and rapid electrodeposition method for stacking magnesium hydroxide layered films. Room-temperature cathodic electrolysis (40 mA cm-2) in a Mg(NO3)2 aqueous solution induces the deposition of ⟨001⟩-oriented Mg(OH) x layered films stacked parallel to the substrate at the deposition rate of ∼2 µm min-1. The obtained Mg(OH) x layered films undergo an overall oriented transformation by heat treatment to form ⟨111⟩-oriented nanoporous MgO films.

Light-Irradiated Electrochemical Direct Construction of Cu2O/CuO Bilayers by Switching Cathodic/Anodic Polarization in Copper(II)-Tartrate Complex Aqueous Solution.

p-CuO with a band gap energy of 1.5 eV, p-Cu2O with a band gap energy of 2.05 eV, and their bilayers were prepared by controlling the potential of anodic and cathodic polarization in a copper(II)-tartrate complex aqueous solution containing copper(II) sulfate hydrate and tartaric acid in the dark and under light irradiation. Electrochemical characteristics of the electrodeposition and the resultant CuO and Cu2O layers were investigated with cyclic voltammetry, chronoamperometry, and Mott-Schottky plots, and the structural and optical characterizations were performed with X-ray diffraction, scanning electron microscopy, and optical absorption spectra measurements. The CuO layer prepared at 0.4-0.7 V was composed of aggregates of granular grains with the monoclinic lattice, and the Cu2O layer composed of coarse grains with the cubic lattice was deposited at -0.4 to 0.6 V. The flat-band potentials were estimated to be 0.145 and -0.1 V (vs Ag/AgCl) for the CuO and Cu2O layers, respectively. The 0.4 µm CuO/1.1 µm Cu2O bilayers could be prepared by switching the electrodeposition potentials of 0.4 and -0.4 V, irrespective of the presence of light irradiation. The photoelectrodeposition under light irradiation enabled the preparation of continuous and dense 1.1 µm Cu2O/0.4 µm CuO bilayer by controlling the potential, while electrodeposition in the dark led to sparse, isolated, and coarse Cu2O grains being deposited. The mechanism for the photoelectrodeposition of the bilayers was discussed based on the energy band alignment at the heterointerface to the Cu-tartrate complex solution.

Helical Pore Alignment on Cylindrical Carbon.

Interest in chiral substances has mainly focused on the substances themselves, but not on the accompanying space, especially regarding the pore alignment. As a method to form both the chiral substance and the accompanying space, cylindrical self-assembly of uniform polystyrene nanoparticles with fructose is carried out in the presence of both carbon and sodium alginate, which is followed by heat treatment in an inert atmosphere. The carbonization generates fructose-derived honeycomb-like carbon walls with helically aligned nanopores left after the polystyrene decomposition. The diffuse reflectance circular dichroism measurements give peaks with opposite signs for the d- and l-fructose-derived cylindrical carbons. Circularly polarized light sensitivity in transient photoconductivity is confirmed apparently in the carbon-based helical structures. This sensitivity as well as straightforward formation of composites with another component to give helicity shows potential applications of the helically aligned pores.

Mechanistic Study on Allylic Arylation in Water with Linear Polystyrene-Stabilized Pd and PdO Nanoparticles.

The catalytic cycle of allylic arylation in water catalyzed by linear polystyrene-stabilized Pd or PdO nanoparticles (PS-PdNPs or PS-PdONPs) was investigated. Stoichiometric stepwise reactions indicated that the reaction did not proceed stepwise on the surface of the catalyst. In the case of the reaction with PS-PdNPs, the leached Pd species is the catalytically active species and the reaction takes place through a similar reaction pathway accepted in the case of a complex catalyst. In contrast, allylic arylation using PS-PdONPs as a catalyst occurs via a Pd(II) catalytic cycle.

Oriented Transformation from Layered Zinc Hydroxides to Nanoporous ZnO: A Comparative Study of Different Anion Types.

Thermal decomposition of layered zinc hydroxides (LZHs) is a simple and convenient way to achieve porous ZnO nanostructures. The type of anion contained in an LZH determines the fundamental characteristics of the LZH and thus affects the formation process of the resulting porous ZnO. Here we report a comparative study on the crystal orientation relationship between LZH precursors and the corresponding porous ZnO products by using well-faceted and highly oriented LZH crystals with three different anions, i.e., NO3-, SO42-, and Cl-. Highly oriented LZH crystals were prepared on layer-by-layer coated indium tin oxide substrates by electrodeposition in aqueous solution and were transformed into porous ZnO by calcination in air. The synthesized materials were characterized by X-ray diffraction, scanning electron microscopy with electron backscatter diffraction, Fourier transformed infrared spectroscopy, and X-ray photoelectron spectroscopy. The layered structure of the highly oriented LZHs was parallel to the substrate surface and all transformed to nanoporous ZnO with a ⟨0001⟩ preferred orientation. The ⟨0001⟩ orientation degree and in-plane orientation of the nanoporous ZnO differed significantly depending on the type of anion but not the decomposition temperature, revealing that the initial formation process of ZnO from the LZHs is crucial. Finally, a possible transformation mechanism explaining the difference in the resulting ZnO orientation by anions (NO3-, SO42-, and Cl-) is discussed on the basis of their layered structure and thermal decomposition processes.

Poly(tetrafluoroethylene)-Stabilized Metal Nanoparticles: Preparation and Evaluation of Catalytic Activity for Suzuki, Heck, and Arene Hydrogenation in Water.

Poly(tetrafluoroethylene)-stabilized Pd nanoparticles (PTFE-PdNPs) were prepared in water with 4-methylphenylboronic acid as a reductant and characterized using powder X-ray diffraction, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Small PdNPs with a fairly uniform size were obtained in the presence of PTFE, whereas aggregation of palladium was observed in the absence of PTFE. PTFE-PdNPs showed high catalytic activity for the Suzuki coupling reaction in water and were reused without any loss of activity. No palladium species were observed by ICP-AES analysis in the reaction solution after the reaction, nor was any change in particle size observed after the recycle experiment. PTFE-PdNPs also exhibited excellent catalytic activity and reusability for the Heck reaction in water. Although palladium species were not detected in the reaction solution after the reaction, aggregates and smaller sizes of PdNPs were observed in the TEM image of the recovered catalyst. PTFE was also useful as the stabilizer of rhodium nanoparticles (RhNPs) prepared by reduction with NaBH4. PTFE-RhNPs showed high catalytic activity and reusability toward arene hydrogenation under mild conditions.

Electrodeposited ZnO-nanowire/Cu2O photovoltaic device with highly resistive ZnO intermediate layer.

Cl-doped ZnO-nanowire (Cl:ZnO-nws)/Cu2O photovoltaic devices were prepared by electrodeposition in aqueous solutions, and the effects of the insertion of the highly resistive ZnO (i-ZnO) layer has been demonstrated by an improvement of the photovoltaic performance. The Cl:ZnO-nws and i-ZnO layer were prepared by electrodeposition in a zinc chloride aqueous solution with saturated molecular oxygen and simple zinc nitrate aqueous solution, respectively. The i-ZnO layer was directly deposited on the Cl:ZnO-nws and suppressed the electrodeposition of the Cu2O layer on the Cl:ZnO-nws. The insertion of the i-ZnO layer between the Cl:ZnO-nws and Cu2O layers induced an improvement in the photovoltaic performance from 0.40 to 1.26% with a 0.35 V open circuit voltage, 7.1 mA·cm(-2) short circuit current density, and 0.52 fill factor due to the reduction of the recombination loss.

Hybrid ZnO/phthalocyanine photovoltaic device with highly resistive ZnO intermediate layer.

We report a hybrid photovoltaic device composed of a 3.3 eV bandgap zinc oxide (ZnO) semiconductor and metal-free phthalocyanine layers and the effects of the insertion of the highly resistive ZnO buffer layer on the electrical characteristics of the rectification feature and photovoltaic performance. The hybrid photovoltaic devices have been constructed by electrodeposition of the 300 nm thick ZnO layer in a simple zinc nitrate aqueous solution followed by vacuum evaporation of 50-400 nm thick-phthalocyanine layers. The ZnO layers with the resistivity of 1.8 × 10(3) and 1 × 10(8) Ω cm were prepared by adjusting the cathodic current density and were installed into the hybrid photovoltaic devices as the n-type and buffer layer, respectively. The phthalocyanine layers with the characteristic monoclinic lattice showed a characteristic optical absorption feature regardless of the thickness, but the preferred orientation changed depending on the thickness. The ZnO buffer-free hybrid 50 nm thick phthalocyanine/n-ZnO photovoltaic device showed a rectification feature but possessed a poor photovoltaic performance with a conversion efficiency of 7.5 × 10(-7) %, open circuit voltage of 0.041 V, and short circuit current density of 8.0 × 10(-5) mA cm(-2). The insertion of the ZnO buffer layer between the n-ZnO and phthalocyanine layers induced improvements in both the rectification feature and photovoltaic performance. The excellent rectification feature with a rectification ratio of 3188 and ideally factor of 1.29 was obtained for the hybrid 200 nm thick phthalocyanine/ZnO buffer/n-ZnO photovoltaic device, and the hybrid photovoltaic device possessed an improved photovoltaic performance with the conversion efficiency of 0.0016%, open circuit voltage of 0.31 V, and short circuit current density of 0.015 mA cm(-2).

Hybrid Cu(2)O diode with orientation-controlled C(60) polycrystal.

We report on a hybrid diode composed of a 2.1 eV bandgap p-cupric oxide (Cu2O) semiconductor and fullerene (C60) layer with a face-centered cubic configuration. The hybrid diode has been constructed by electrodeposition of the 500 nm thick Cu2O layer in a basic aqueous solution containing a copper acetate hydrate and lactic acid followed by a vacuum evaporation of the 50 nm thick C60 layer at the evaporation rate from 0.25 to 1.0 Å/s. The C60 layers prepared by the evaporation possessed a face-centered cubic configuration with the lattice constant of 14.19 A, and the preferred orientation changed from random to (111) plane with decrease in the C60 evaporation rate from 1.0 to 0.25 Å/s. The hybrid p-Cu2O/C60 diode showed a rectification feature regardless of the C60 evaporation rate, and both the rectification ratio and forward current density improved with decrease in the C60 evaporation rate. The excellent rectification with the ideality factor of approximately 1 was obtained for the 500 nm thick (111)-Cu2O/50 nm thick (111)-fcc-C60/bathocuproine (BCP) diode at the C60 evaporation rate of 0.25 Å /s. The hybrid Cu2O/C60 diode prepared by stacking the C60 layer at the evaporation rate of 0.25 Å/s revealed the photovoltaic performance of 8.7 × 10(-6)% in conversion efficiency under AM1.5 illumination, and the conversion efficiency changed depending on the C60 evaporation rate.

Preparation of core/shell and hollow nanostructures of cerium oxide by electrodeposition on a polystyrene sphere template.

Core/shell nanostructures of polystyrene (PS)/CeO2 have been prepared on conductive glass substrates by using a novel electrochemical route consisting of (i) the electrophoretic deposition of a PS sphere monolayer on the substrate and (ii) the following potentiostatic electrodeposition of CeO2 on the PS sphere template in Ce(NO3)3 aqueous solutions. The structural morphologies of the deposit changed drastically depending on the Ce(NO3)3 concentration; i.e., spherical and needlelike shells were deposited. The deposit was formed only on the PS sphere surface because of an interaction between cationic cerium species and a sulfate group that was immobilized on the PS sphere surface. The spherical shell layer was assigned as CeO2, and the needlelike shells were composed of Ce(OH)3 needles formed on the CeO2 layer surface, indicating that the deposit species changes from CeO2 to Ce(OH)3 during electrodeposition only in a 1 mM Ce3+ solution. Deposition of Ce(OH)3 would begin when electrogenerated hydrogen peroxide was consumed by decomposition under reductive conditions and could no longer oxidize Ce3+ ions. The corresponding CeO2 hollow shells were obtained by thermal elimination of the PS sphere core and transformation of Ce(OH)3 into CeO2 while keeping their original shapes.