Faceting of Au NPs is induced by a heteroepitaxial junction on anatase TiO₂(001) nanoplate array. Light irradiation of the plasmonic electrode generates current for water oxidation at λ < 900 nm with a maximum efficiency of 0.39% at λ = 600 nm.

Abstract A heterodimeric leucine zipper (Lz)–based peptide hybrid was utilized as a molecular adhesive to bind two types of gold nanocrystals with different shapes. An acidic leucine zipper (LzE) and a basic leucine zipper (LzK) peptides with terminal cysteine are respectively adsorbed to the surface of spherical gold nanoparticles (LzE–Au NPs) and gold nanocubes (LzK–Au NCs). Transmission electron microscope (TEM) observation and visible (Vis) absorption spectroscopy revealed that LzE–Au NPs and LzK–Au NCs are selectively self-assembled in water. The dynamic self-assembly behavior is also confirmed by in-situ fluorescence resonance energy transfer between fluorescence dyes connected to LzE and LzK peptides and other control experiments.

Facile synthesis of single-crystalline MnO2 nanowire arrays with high photothermal catalytic activity Tetsuro Soejima,a,b* Haruki Inoue,b Keigo Egashira,b and Hiroaki Tadaa,b* A simple process has been developed to form single-crystalline...

Radial ZnO mesocrystals consisting of tapered ZnO nanowires (NWs) were synthesized by a liquid-phase reaction, which proceeds via the preferential zone-axis growth to ZnO NWs, and self-assembling of linear ZnO NW dimers.

The artificial photosynthesis of H2O2 from water and O2 presents a sustainable route for the production. Remarkable progress in the rate of reaction has recently been achieved mainly by using...

Highly monodisperse amorphous manganese oxide (MnOx) nanospheres with diameter of ca. 300nm have been obtained from ammonia aqueous solution of KMnO4 at room temperature. The amorphous MnOx nanospheres successfully converted to monodisperse K-OMS-2 (cryptomelane) and K-OMS-2/Mn2O3 nanoraspberries through calcination process at 600 and 800C, respectively. Analyzing the structure of such amorphous MnOx has been a challenge because fewer reports are available to examine amorphous structure. Thus, shape, crystallinity, and structure of the amorphous and crystalline MnOx nanostructures were characterized in detail by X-ray diffraction (XRD), thermogravimetry/differential thermal analysis (TG/DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and energy dispersive spectroscopy (EDS). We discussed a plausible formation mechanism of amorphous MnOx nanospheres based on the investigations. The obtained MnOx nanostructures have been demonstrated to possess oxidative degradation ability of Rhodamine B (RhB) under acidic aqueous condition without any additives such as chemical oxidizing agents and UV and/or visible light irradiation. RhB degradation rate of amorphous MnOx nanospheres was about one hundred times faster than that of K-OMS-2 nanoraspberries. (c) 2017 Elsevier Inc. All rights reserved.

One-dimensional growth of copper (Cu) is observed when Cu is deposited on cuprous iodide (CuI) films at elevated temperatures by thermal evaporation in high vacuum. The morphology, crystallinity, and chemical composition were examined for the samples using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Straight single-crystalline Cu nanowires can be formed on polycrystalline CuI films at 200 degrees C. Anisotropic growth of Cu in one-dimension was promoted by enhancing grain growth and continuity of CuI films. At a lower temperature of 100 degrees C, fuzzy branching nanowires were grown on the surface of CuI films, enabling to simply fabricate a self-supporting, highly porous film of Cu. It is revealed that a Cul film serves as a functional substrate to synthesize nanostructured Cu at low temperatures. Possible growth processes are proposed to explain the observed morphology evolution of Cu with respect to synthesis conditions. The characterization of water wettability showed that the hydrophobicity was remarkably enhanced due to the formation of nanostructured Cu on the CuI films. (c) 2017 Elsevier Ltd. All rights reserved.

Silver-silver halides (Ag-AgX, X = Cl, Br, I) have emerged as a new type of visible-light photocatalyst for solar-to-chemical transformations. The key to improving the activity of the plasmonic photocatalyts is the compatibility of local electric field enhancement (LEFE) and effective utilization of the sunlight as the energy source. A Ag nanoparticle (NP) possesses an intense LEFE effect, while the absorption peak is situated near the blue edge of the visible region. On the other hand, the Au NP has an absorption matching well the solar spectrum, but the LEFE is much smaller than that of a Ag NP. The optical property of a Au-x-Ag1-x alloy NP varies between those of Ag and Au NPs depending on the composition x, and thus, Au-x-Ag1-x alloy NP-incorporated AgX (Au-x-Ag1-x@AgX) can be a promising plasmonic photocatalyst. At the first step, gold ion-doped AgBr NPs are formed on mesoporous TiO2 film by the successive ionic layer adsorption and reaction (SILAR) method. At the second step, UV-light irradiation (lambda > 320 nm) of the sample in methanol yields Au-x-Ag1-x alloy particles having diameter of similar to 5 nm in the interior of AgBr with crystallite size of similar to 50 nm. The peak wavelength for the localized surface plasmon resonance can be tuned in the range between 500 and 600 nm through the alloy composition. On the basis of the experimental and density functional theory calculation results, we propose a plausible reaction mechanism.

The development of a facile growth method of gold nanocrystals with a controlled shape is of crucial importance to expand the potential applications of gold nanoarchitectures which have various unique and useful physicochemical properties. Here, we report the site-preferential formation of gold nanostructures with various shapes on Si substrates. When a Si wafer covered with cetyltrimethylammonium bromide (CTAB, an organic salt) is immersed in Au center dot OH)(4)(-) aqueous solution and immediately photoirradiated, dendritic gold nanostructures grow on the surface of the Si wafer. Interestingly, the gold nanodendrites preferentially grow on scratched portions drawn by using a pen-type diamond glass cutter on the Si wafer. The shape of gold nanocrystals depends on the structure of both quaternary alkylammonium cations and halide anions, which are components of the organic salt film, and gold nanostructures with various shapes are successfully obtained at the scratched portions. It is revealed that concerted mechanisms of photoreduction of Au3+ ions and a new type of galvanic displacement reaction between Si and Au(OH)(4)(-) cause the site-preferential growth of gold nanoarchitectures.

Dissipative structures are macroscopic or even larger ordered structures that emerge under conditions far from thermodynamic equilibrium. In contrast, molecular self-assembly has been investigated near at the thermodynamic equilibrium, which provides basically smaller, nano-to-micron sized structures. In terms of the formation principles, there exists an essential gap between the dissipative structures and molecular self-assemblies. To fill this gap, molecular self-assembly of light-reducible organic-inorganic ion pairs was investigated under far-from-equilibrium conditions. When solid films of tetraalkylammonium hexafluorophosphate were immersed in aqueous Au(OH)4(-) and immediately photoirradiated, gold nanowires are formed at the solid-aqueous interface. On the other hand, such nanowires were not formed when the photoirradiation was conducted for the specimens after a prolonged immersion period of 60 min. These observations indicate spontaneous growth of dissipative nanofibrous self-assemblies consisting of light-reducible ion pairs [tetraalkylammonium ion][Au(OH)4(-) at the interface and their photoreduction to give developed nanowires. These nanowires are not available by the photoreduction of Au(OH)4(-) ions under conditions near at the thermodynamic equilibrium. A picture for the dissipative nanostructures is obtained: the formation of amphiphilic light-reducible nanowire structures is based on the static self-assembly near at the thermodynamic equilibrium, whereas their spontaneous, anisotropic growth from the interface to the aqueous phase is directed by dynamic, dissipative self-assembly phenomena under the far-from-equilibrium conditions. Thus, the both elements of dissipative self-assembly (dynamic) and static molecular self-assembly fuse together at the nanoscale, which is an essential feature of the dissipative nanostructures.

Graphene (oxide)/TiO2 composite materials have attracted widespread attention because of their scientific and technological importance as, for example, photocatalysts or electronic materials. These composites are usually prepared using high-temperature and/or slow synthetic procedures such as the hydrothermal method. Here, we demonstrate a low-temperature and relatively rapid synthesis of a graphene oxide/TiO2 composite. Graphene oxide sheets decorated with anatase TiO2 nanoparticles are successfully obtained by refluxing graphene oxide sheets dispersed in an aqueous TiOSO4 ethanol solution at 80 degrees C for 2 h. The graphene oxide is reduced during photocatalytic reduction of the TiO2 deposited on the surface of the graphene oxide. The reduced graphene mdde/TiO2 composite shows very high photocatalytic activity as compared with pure TiO2 and nonreduced graphene oxide/TiO2.

CuO/ZnO nanocomposite materials have attracted widespread attention because of their scientific and technological importance as, for example, photocatalysts, gas and humidity sensors, catalysts for H-2 production and organic synthesis, and solar cells. High-temperature and/or complicated multistep processes are usually used to prepare these composites. Here we demonstrate a low-temperature and facile one-step synthesis of CuO nanoflowers/ZnO nanorods composite arrays via an alkaline vapor oxidation process. The CuO/ZnO composite nanoarrays show high electrocatalytic activity toward glucose oxidation. (c) 2013 Elsevier B.V. All rights reserved.

A far-from-equilibrium strategy is developed to synthesize coral-like nanostructures of TiO2 on a variety of surfaces. TiO2 nanocoral structures consist of anatase base film and rutile nanowire layers, and they are continuously formed on substrates immersed in aqueous TiOSO4-H2O2. The sequential deposition of TiO2 starts with hydrolysis and condensation reactions of titanium peroxocomplexes in the aqueous phase, resulting in deposition of amorphous film. The film serves as adhesive interface on which succeeding growth of rutile nanowires to occur. This initial deposition reaction is accompanied by shift in pH of the reaction media, which is favorable condition for the growth of rutile nanocrystals. During the growth of rutile nanocoral layers, the amorphous base films are transformed to anatase phase. These sequential deposition reactions occur at temperatures as low as 80 degrees C, and the mild synthetic condition allows the use of a wide range of substrates such as ITO (indium tin oxide), glass, and even organic polymer films. The thickness of nanocoral layer is controllable by repeating the growth reaction of rutile nanocorals. TiO2 nanocorals show photocatalytic activity as demonstrated by site-specific reduction of Ag(I) ions, which proceeds preferentially on the rutile nanowire layer. The rutile nanowire layer also shows photocatalytic decomposition of acetaldehyde, which is promoted upon increase of the thickness of the nanowire layer. The use of temporally transforming reaction media allows the formation of biphasic TiO2 nanocoral structures, and the concept of nonequilibrium synthetic approach would be widely applicable to developing structurally graded inorganic nanointerfaces.

Gold nanoparticles were fabricated by reduction of highly concentrated Au(III) ions (200 mM) with casein proteins from milk. The gold nanoparticles were converted to nanoparticle-powders after washing and subsequent vacuum drying without aggregation. The nanoparticle-powders completely re-dispersed in aqueous solution, and stable colloidal gold nanoparticles were obtained. UV-vis extinction spectra and dynamic light scattering (DLS) measurements revealed that large assemblies (size, ca. 3 mu m) and subaggregates (size, <0.51 mu m) composed of gold nanoparticle-casein protein chain-Au(III) ion were dynamically formed and disintegrated over the course of the growth of the gold nanoparticles. Fourier transform infrared (FT-IR) spectra indicated conformational changes of casein proteins induced by the interaction of casein protein-Au(III) ion and -gold nanoparticle. Finally, rapid, one-pot, and highly concentrated synthetic procedures of gold and silver nanoparticle powders protected by casein (mean diameters below 10 nm) were successfully developed using 3-amino-1-propanol aqueous solutions as reaction media. Dense colloidal gold (40 g L-1) and silver (22 g L-1) nanoparticle aqueous solutions were obtained by re-dispersing the metal nanoparticle powders. (C) 2011 Elsevier Inc. All rights reserved.

A novel one-pot low temperature preparation of Fe-doped anatase-rutile TiO2 (Fe-TiO2) films is demonstrated using plasma electrolytic oxidation (PEO). Pale yellow TiO2 films are obtained by PEO treatment of Ti metals in the electrolyte dispersing TiO2 and Fe2O3 particles. The oxidized layer on Ti metal have a sponge-like structure with thickness and pore size of 10 and 0.1-1 mu m, respectively. Investigation by X-ray diffraction, X-ray photoelectron spectroscopy, and UV-Vis absorption spectroscopy all indicate that dissolved Fe3+ ions in the strong acidic electrolyte are doped into the TiO2 structure during PEO. The photocatalytic activity of Fe-TiO2 samples was investigated by studying the photocatalytic decomposition of acetaldehyde. Fe-TiO2 samples doped with optimum Fe content show visible light photocatalytic activity and further increased photocatalytic activity under UV illumination compared with that of pure TiO2 films.

Supported catalysts are widely used in industry and can be optimized by tuning the composition and interface of the metal nanoparticles and oxide supports. Rational design of metal-metal oxide interfaces in nanostructured catalysts is critical to achieve better reaction activities and selectivities. We introduce here a new class of nanocrystal tandem catalysts that have multiple metal-metal oxide interfaces for the catalysis of sequential reactions. We utilized a nanocrystal bilayer structure formed by assembling platinum and cerium oxide nanocube monolayers of less than 10 nm on a silica substrate. The two distinct metal-metal oxide interfaces, CeO(2)-Pt and Pt-SiO(2), can be used to catalyse two distinct sequential reactions. The CeO(2)-Pt interface catalysed methanol decomposition to produce CO and H(2), which were subsequently used for ethylene hydroformylation catalysed by the nearby Pt-SiO(2) interface. Consequently, propanal was produced selectively from methanol and ethylene on the nanocrystal bilayer tandem catalyst. This new concept of nanocrystal tandem catalysis represents a powerful approach towards designing high-performance, multifunctional nanostructured catalysts.

CuO nanobelt arrays supported on copper substrates are synthesized by a simple and one-pot low-temperature vapor oxidation method. The CuO nanobelt arrays show high electrocatalytic activity towards glucose oxidation.

A room-temperature nanocarving strategy is developed for the fabrication of complex gold nanoplates having corolla- and propeller-like architectures. It is based on the simultaneous growth and etching of gold nanoplates in aqueous solution, which occur in the course of photoreduction of Au(OH)(4)(-) ions. The presence of bromide ion, poly(vinylpyrrolidone) (PVP), and molecular oxygen is indispensable, where bromide ions play multiple roles. First, they promote formation of nanoplate structures by forming adlayers on the fcc(111) surface. Second, they facilitate oxidative dissolution of gold nanocrystals by converting the oxidized Au(I) species to soluble AuBr(2)(-) ions, which lead to the formation of ultrathin nanocrevasses. PVP also stabilizes the nucleation of gold nanoplates. Although the overall reactions proceed in one-pot, the crystal growth and etching show interplay and occur with different kinetics due to changes in the concentration of Au(OH)4- and other species with time. Corolla- or propeller-like gold nanoplates formed under these conditions are single-crystalline, as indicated by selected area electron diffraction patterns and the observation of moire fringes. The morphology of corolla- or propeller-like gold nanoplates is controllable depending on the concentration of bromide ion and PVP in the aqueous mixture. On the basis of these results, a preliminary mechanism is proposed which involves the concurrent crystal growth and oxidative etching on the surface of nanocrystals.

An aqueous-phase synthesis of gold nanotadpoles by using bilayer membranes as growth regulating factor is newly developed. The gold nanotadpoles are formed by photoreduction of Au(OH)(4)(-) in aqueous bilayer dispersion. The outgrowth of tails occurred from spherical nanoparticles, which are regulated depending on the photoirradiation time.

Nanometer-sized gold particles with varying mean size from 3.2 to 12.2 nm were loaded on the surfaces of TiO2 particles in a highly dispersed state with the loading amount maintained constant (0.46 +/- 0.02 mass %) using the deposition-precipitation method. Light irradiation (lambda(ex) > 300 nm) to a deaerated ethanol TiO2 particle suspension containing elemental sulfur (S-8) led to the energetically uphill reduction of S-8 to H2S. It has been found that this reaction is dramatically enhanced with such a low level of Au loading on TiO2 and that the zero-order rate constant of reaction increases with decreasing mean size of Au nanoparticles (d). The effects of reaction parameters ( substrate concentration, light intensity, temperature) on the rate of reaction were studied to infer the essential reaction mechanism. Further, a kinetic analysis has led to a conclusion that the increase in the rate of reaction with decreasing d results from the improvement of the charge separation efficiency.

Ultrathin, single-crystal line gold nanosheets with thickness of ca. 10nm are successfully obtained in water by photoreduction of Au(OH)(4)(-) ions at the surface of ionic liquid (IL) mu-droplets. The nanosheets produced at the interface are spontaneously extracted into the ionic liquid phase, which effectively prevents the formation of thicker nanoplates.

Au particles (mean size ca. 3 nm) supported on TiO2 particles were irradiated by UV light (> 300 nm) in aqueous solutions at 278 K. Photoinduced dissolution of Au nanoparticles followed by redeposition occurred in aqueous solutions containing halogen ions. The dissolution of An nanoparticles yielded a Au(III) complex with a halogen ion; subsequent reduction of the Au(III) complex caused precipitation of larger An particles on TiO2,. (c) 2005 Elsevier Inc. All rights reserved.

The aim of this study is to prepare Au clusters with a mean size (d) of less than 3.0 nm, at which nonmetallic properties can be expected to appear. Au clusters (d < 3.0 nm) have been formed rapidly (<2 min) on TiO2 surfaces by a two-step method consisting of Au(III)-complex chemisorption and subsequent photoreduction (lambda(ex) > 300 nm) at temperatures below 25 degreesC. In the photoreduction of the Au(III) complex to Au-0, chemisorbed and physisorbed H2O on the TiO2 surface acts as a reductant. This method also enables us to produce Au clusters selectively at the UV-irradiated TiO2 surfaces.

当該年度においては，ハロゲン化銀の保護剤を用いない形状制御合成について検討した。具体的には，室温において，硝酸銀とハロゲン化ナトリウムの水溶液を混合し，撹拌しながらこれらの二種類の溶液を混合した。硝酸銀とハロゲン化ナトリウム中の銀イオンとハロゲン化物イオンのモル比を変化させて種々の実験を行った。その結果，種々のハロゲン化物イオンに対応するハロゲン化銀ナノ粒子が生成した。得られた粒子について電子顕微鏡観察を行ったところ，臭化銀，塩化銀，ヨウ化銀において，それぞれナノシート，ナノキューブ，形状の崩れたナノシートを形成していることがわかった。 また，昨年度の成果において金と臭化銀の接合化に成功したことから，この接合ナノ粒子を用いて表面増強ラマン散乱分光への応用を検討した。すなわち，接合ナノ粒子分散液をガラス基板に固定化し，そこに色素溶液を滴下してラマン測定を行った。その結果，単純な色素乾燥薄膜と比較して，明らかな表面増強結果が得られた。色素溶液について低濃度と高濃度条件について検討したところ，ある濃度までは濃度とシグナルに比例関係が見られたが，特定の濃度以上ではシグナル強度の飽和が見られた。これは，電場増強された接合界面と，その影響を受ける色素分子の距離に関係があるものと考えられる。また，この結果は，接合界面が増強されたラマン散乱光に関係していることを直接示した結果であると言える。 ハロゲン化銀と金の接合粒子の合成を行っているときに，20面体の金ナノ粒子が生成することを発見した。種々の条件について検討したところ，水溶性高分子であるポリビニルピロリドン（PVP）とハロゲン化物イオンが共存する環境下で金イオンの光還元を行うと，九角形金ナノシートや20面体の金ナノ粒子などが得られることがわかった。この結果は，ハロゲン化物イオンとPVPの協奏的な保護作用によるものであると結論付けた。