Ultrathin Hexagonal Hybrid Nanosheets Synthesized by Graphene Oxide‐Assisted Exfoliation of β‐Co(OH)2 Mesocrystals

In the present study, we report the synthesis of a high‐quality, single‐crystal hexagonal β‐Co(OH)₂ nanosheet, exhibiting a thickness down to ten atomic layers and an aspect ratio exceeding 900, by using graphene oxide (GO) as an exfoliant of β‐Co(OH)₂ nanoflowers. Unlike conventional approaches using ionic precursors in which morphological control is realized by structure‐directing molecules, the β‐Co(OH)₂ flower‐like superstructures were first grown by a nanoparticle‐mediated crystallization process, which results in large 3D superstructure consisting of ultrathin nanosheets interspaced by polydimethoxyaniline (PDMA). Thereafter, β‐Co(OH)₂ nanoflowers were chemically exfoliated by surface‐active GO under hydrothermal conditions into unilamellar single‐crystal nanosheets. In this reaction, GO acts as a two‐dimensional (2D) amphiphile to facilitate the exfoliation process through tailored interactions between organic and inorganic molecules. Meanwhile, the on‐site conjugation of GO and Co(OH)₂ promotes the thermodynamic stability of freestanding ultrathin nanosheets and restrains further growth through Oswald ripening. The unique 2D structure combined with functionalities of the hybrid ultrathin Co(OH)₂ nanosheets on rGO resulted in a remarkably enhanced lithium‐ion storage performance as anode materials, maintaining a reversible capacity of 860 mA h g^?1 for as many as 30 cycles. Since mesocrystals are ubiquitous and rich in morphological diversity, the strategy of the GO‐assisted exfoliation of mesocrystals developed here provides an opportunity for the synthesis of new functional nanostructures that could bear importance in clean renewable energy, catalysis, photoelectronics, and photonics.     

Self-organized hierarchical ZnS/SiO(2) nanowire heterostructures

Novel hierarchical heterostructures formed by wrapping ZnS nanowires with highly dense SiO(2) nanowires were successfully synthesized by a vapor-liquid-solid process. The as-synthesized products were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy equipped with an energy-dispersive X-ray spectrometer. Studies indicate that a typical hierarchical ZnS/SiO(2) heterostructure consists of a single-crystalline ZnS nanowire (core) with diameter gradually decreasing from several hundred nanometers to 20 nm and adjacent amorphous SiO(2) nanowires (branches) with diameters of about 20 nm. A possible growth mechanism was also proposed for the growth of the hierarchical heterostructures.     

Synthesis of TiO2 nanocoral structures in ever-changing aqueous reaction systems

A far-from-equilibrium strategy is developed to synthesize coral-like nanostructures of TiO(2) on a variety of surfaces. TiO(2) nanocoral structures consist of anatase base film and rutile nanowire layers, and they are continuously formed on substrates immersed in aqueous TiOSO(4)-H(2)O(2). The sequential deposition of TiO(2) 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 °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. TiO(2) 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 TiO(2) nanocoral structures, and the concept of nonequilibrium synthetic approach would be widely applicable to developing structurally graded inorganic nanointerfaces.     

Silicon-silica nanowires, nanotubes, and biaxial nanowires: inside, outside, and side-by-side growth of silicon versus silica on zeolite

It was demonstrated that zeolite can be used as a pseudo-template to grow very fine and uniform silicon nanostructures via disproportionation reaction of SiO by thermal evaporation. Three distinct types of composite nanowires and nanotubes of silicon and silica were grown on the surfaces of zeolite Y pellets. The first type is formed by an ultrafine crystalline silicon nanowire sheathed by an amorphous silica tube (a silicon nanowire inside a silica nanotube). The second type is formed by a crystalline silicon nanotube filled with amorphous silica (a silicon nanotube outside a silica nanowire). The third type is a biaxial silicon-silica nanowire structure with side-by-side growth of crystalline silicon and amorphous silica. These silicon nanostructures exhibit unusually intense photoluminescence (in comparison to ordinary silicon nanowires).     

Helical structure of single-crystalline ZnGa2O4 nanowires

Two unique helical zinc gallate (ZnGa2O4) nanostructures were synthesized by thermal evaporation using the zinc selenide (ZnSe) nanowires; helical ZnGa2O4 nanowire rolls either on a straight ZnSe nanowire support or without any support. They all consist of single-crystalline cubic ZnGa2O4 crystals without any dislocation over the entire helical structure and have four equivalent growth directions of 011 with the axial direction of [001]. We suggest that the lattice matching with the ZnSe nanowires would be an important factor in determining the growth direction of the helical ZnGa2O4 nanowires.     

Facile and mild solution synthesis of Cu2O nanowires and nanotubes driven by screw dislocations

We report a green synthesis of Cu(2)O nanowires and nanotubes in aqueous solution by reducing Cu(2+) to Cu(+) with glucose or fructose via Fehling's reaction. The screw dislocation-driven growth of Cu(2)O nanowires and nanotubes is confirmed by imaging the dislocation contrast, the Eshelby twist associated with dislocations and the spontaneously formed hollow nanotubes.     

Inorganic semiconductor nanowires: rational growth, assembly, and novel properties

Rationally controlled growth of inorganic semiconductor nanowires is important for their applications in nanoscale electronics and photonics. In this article, we discuss the rational growth, physical properties, and integration of nanowires based on the results from the authors' laboratory. The composition, diameter, growth position, and orientation of the nanowires are controlled based on the vapor-solid-liquid (VLS) crystal growth mechanism. The thermal stability and optical properties of these semiconductor nanowires are investigated. Particularly, ZnO nanowires with well-defined end surfaces can function as room-temperature ultraviolet nanolasers. In addition, a novel microfluidic-assisted nanowire integration (MANI) process was developed for the hierarchical assembly of nanowire building blocks into functional devices and systems.     

Tl_2O_3/聚-N-乙烯基咔唑复合纳米线的研究

微型化是纳米科技发展的关键驱动力之一，然而使用现行的光刻技术生产大规模集成电路器件的技术已经接近极限尺寸（～0．8μm）．1982年STM的研制成功使得在纳米尺寸上进行操作成为可能[1－3]同时，LB技术正在应用于纳米粒子薄膜的制备中[4]．进一步利用Iangmuir单层膜诱导控制     

Efficient reduction of graphene oxide catalyzed by copper

We report that copper thin films deposited on top of graphene oxide (GO) serve as an effective catalyst to reduce GO sheets in a diluted hydrogen environment at high temperature. The reduced GO (rGO) sheets exhibit higher effective field-effect hole mobility, up to 80 cm(2) V(-1) s(-1), and lower sheet resistance (13 kΩ □(-1)) compared with those reduced by reported methods such as hydrazine and thermal annealing. Raman and XPS characterizations are addressed to study the reduction mechanism on graphene oxide underneath copper thin films. The level of reduction in rGO sheets is examined by Raman spectroscopy and it is well correlated with hole mobility values. The conductivity enhancement is attributed to the growth of the graphitic domain size. This method is not only suitable for reduction of single GO sheets but also applicable to lower the sheet resistance of Langmuir-Blodgett assembled GO films.     

Tl2O3/聚-N-乙烯基咔唑复合纳米线的研究

Stable monolayers of electropolymerized poly-N-vinylcarbazole (EPVK) and arachidic acid(AA) are obtained on a subphase of alkaline Tl2O3 colloidal solutions. As revealed by the atomic force microscope, there is phase separation in the mixed LB monolayers. Transmission electron microscopic observations reveal that ordered arrays of composite Tl2O3/Epvk nanowires are formed in the mixed monolayers. Formation of the composite nanowire arrays is attributed to the ordered adsorption of Tl2O3 colloidal particles along the polycationic EPVK chains. The composite nanowire array is 3.2nm wide with a spacing of 2.7nm.The composite nanowire arrays can also be formed when pure EPVK is used. Composite LB multilayers of Tl2O3/EPVK nanowire arrays are prepared. The bilayer spacing is 5.54nm.The present study is of importance to the fabrication of inorganic semiconductor/functional polymer composite nanowires.     

Bioinspired synthesis of calcium carbonate hollow spheres with a nacre-type laminated microstructure

In this Article, we combine the characters of hyperbranched polymers and the concept of double-hydrophilic block copolymer (DHBC) to design a 3D crystal growth modifier, HPG-COOH. The novel modifier can efficiently control the crystallization of CaCO(3) from amorphous nanoparticles to vaterite hollow spheres by a nonclassical crystallization process. The obtained vaterite hollow spheres have a special puffy dandelion-like appearance; that is, the shell of the hollow spheres is constructed by platelet-like vaterite mesocrystals, perpendicular to the globe surface. The cross-section of the wall of a vaterite hollow sphere is similar to that of nacres in microstructure, in which platelet-like calcium carbonate mesocrystals pile up with one another. These results reveal the topology effect of the crystal growth modifier on biomineralization and the essential role of the nonclassical crystallization for constructing hierarchical microstructures.     

Dye-sensitized solar cells based on anatase TiO2 nanoparticle/nanowire composites

Dye-sensitized solar cells were fabricated based on the composites of anatase TiO2 nanoparticles and single crystalline anatase TiO2 nanowires. Nanoparticle/nanowire composites can possess the advantages of both building blocks, i.e., the high surface area of nanoparticle aggregates and the rapid electron transport rate and the light scattering effect of single-crystalline nanowires. Three different composites were prepared with 5 wt %, 20 wt %, and 77 wt % nanowires, respectively. The performances of composite solar cells were compared with pure nanoparticle cells at a series of film thickness. With low nanowire concentrations (5 wt % and 20 wt %), the composite films maintain similar specific surface area as the pure nanoparticle films, while the composite cells show higher short-circuit current density and open-circuit voltage. An enhancement of power efficiency from 6.7% for pure nanoparticle cells to 8.6% for the composite cell with 20 wt % nanowires has been achieved under 1 Sun AM1.5 illumination (100 mW/cm2). For the composite film with 77 wt % nanowires, the nanowires became the major phase. Their less compact packing resulted in significant decrease of the specific surface area, and thus the current density. However, with the increase of film thickness, the current density showed a continuous increase in the whole thickness range up to 17 microm, indicating the improved electron diffusion length due to the formed nanowire network. The nanowires also helped to preserve crack-free thick films. These results show that employing nanoparticle/nanowire composites represents a promising approach for further improving the efficiencies of sensitized solar cells.     

A novel chemical route to SiO_2 nanowires

A white substance was got by directly heating TiSi powder on Ti foil, under Ar+O2 atmosphere. ED, EDX, SEM and HRTEM studies reveal that the white substance consists of amorphous SiO2nanowires of smooth surface and uniform diameter (40-90 nm). X-ray-induced luminescent emission experiment shows that two broad peaks are at 430 and 570 nm. A one-dimensional growth mechanism, on the basis of the one-dimensional thermal flow during nanowire formation, is discussed.     

Solid state coordination chemistry: construction of 2D networks and 3D frameworks from phosphomolybdate clusters and binuclear Cu(II) complexes. The syntheses and structures of [(Cu2(tpypyz)(H2O)2)(Mo5O15)(HOPO3)2].nH2O [n = 2, 3; tpypyz = tetra(2-pyridyl)pyrazine

The hydrothermal reaction of MoO3, Cu(C2H3O2)2.H2O, tpypyz, H3PO4 and H2O yields a 2D material, [(Cu2(tpypyz)(H2O)2)(Mo5O15)(HOPO3)2].2H2O (1.2H2O), constructed from (Mo5O15(HOPO3)2)4- clusters linked through (Cu2(tpypyz)(H2O)2)2+ components; in contrast, use of Cu2O in the synthesis in place of Cu(C2H3O2)2.H2O yields a 3D material [(Cu2(tpypyz)(H2O)2)(Mo5O15)(HOPO3)2].3H2O (2.3H2O), constructed from the same building blocks as 1.2H2O.     

正丁基氯化镁还原氧化石墨烯的表征

采用元素分析、红外光谱(FTIR)、X射线光电子能谱(XPS)、拉曼光谱、X射线衍射(XRD)、固体¹³C核磁共振波谱(¹³C MAS NMR)、热失重分析(TGA)、导电率测试以及原子力显微镜(AFM)等手段对正丁基氯化镁还原的氧化石墨烯进行了系统的表征. 结果表明, 正丁基氯化镁可以有效还原氧化石墨烯, 随着其用量的增加, 氧化石墨烯还原程度增加, 碳/氧摩尔比升高, 片层间距减小, 热稳定性增强, 导电率增大(可达3.6×10² S/m). 还原后部分氧化石墨烯片层发生聚集.     

Low-temperature synthesis of single crystalline Ag2S nanowires on silver substrates

We report on the successful synthesis of silver sulfide (Ag(2)S) nanowires by a simple and mild gas-solid reaction approach. For the nanowire synthesis, a preoxidized silver substrate is exposed to an atmosphere of an O(2)/H(2)S mixture at room temperature or slightly above. The resulting Ag(2)S nanowires are phase pure with a monoclinic crystal structure and have diameters of a few tens of nanometers and lengths up to 100 mum. The influence of reaction conditions on the diameter, length, and morphology of the Ag(2)S nanowires has been studied by a number of structural and spectroscopic techniques. The nanowire growth mechanism on the Ag substrate has been discussed, which is likely characterized by continuous deposition at the tip. Additionally, we demonstrate thinning and cutting of individual Ag(2)S nanowires with electron beams and laser beams, which are potentially useful for nanowire manipulation and engineering.     

High solar-light photocatalytic activity of using Cu3Se2/rGO nanocomposites synthesized by a green co-precipitation method

Current work presents a facile, cost-effective, and green method to synthesize copper selenide nanostructures and copper selenide/graphene nanocomposites. The products were synthesized by a co-precipitation method by glycine amino acid as a green surfactant and graphene oxide (GO) sheets as a graphene source. X-ray diffraction patterns (XRD) of the products indicated that the products were Cu₂Se₃ with tetragonal phase. Fourier transform infrared (FTIR) spectroscopy and the XRD patterns indicated that the GO sheets were changed into reduced GO (rGO) during the synthesis process. Scanning and transmission electron microscopy (SEM and TEM) images showed the nanoparticles (NPs) that were decorated on rGO sheets had the significantly smaller size in compared to the pristine NPs. UV-vis results revealed that, the absorption peak of the products were in the visible region with a band-gap value between 1.85 eV and 1.95 eV. Finally, the products were applied as photocatalytic materials to remove Methylene Blue (MB) dye under solar-light and visible-light irradiation conditions. It was observed; the rGO had a significant role in enhancing the photocatalytic performance of the products and Cu₂Se₃/rGO (15%) could degrade more than 91% and 73% of MB only during 1 h under solar-light and visible-light sources, respectively.     

Template-directed synthesis of ordered single-crystalline nanowires arrays of Cu2ZnSnS4 and Cu2ZnSnSe4

Highly ordered quaternary semiconductor Cu(2)ZnSnS(4) nanowires array have been prepared via a facile solvothermal approach using anodic aluminum oxide (AAO) as a hard template. The as-prepared nanowires are uniform and single crystalline. They grow along either the crystalline [110] or [111] direction. The structure, morphology, composition, and optical absorption properties of the as-prepared Cu(2)ZnSnS(4) samples were characterized using X-ray powder diffraction, transmission electron microscopy, energy dispersive X-ray spectrometry, scanning electron microscopy, and UV-vis spectrometry. A possible formation mechanism of the nanowire arrays is proposed. Governed by similar mechanism, we show that Cu(2)ZnSnSe(4) nanowire array with similar structural characteristics can also be obtained.     

Controlled growth of large-area, uniform, vertically aligned arrays of alpha-Fe2O3 nanobelts and nanowires

Vertically aligned iron oxide nanobelt and nanowire arrays have been synthesized on a large-area surface by direct thermal oxidation of iron substrates under the flow of O(2). The effects of reactive gas pressure, composition, and temperature have been systematically studied. It was found that nanobelts (width, tens of nanometers; thickness, a few nanometers) are produced in the low-temperature region (approximately 700 degrees C) whereas cylindrical nanowires tens of nanometers thick are formed at relatively higher temperatures (approximately 800 degrees C). Both nanobelts and nanowires are mostly bicrystallites with a length of tens of micrometers which grow uniquely along the [110] direction. The growth habits of the nanobelts and nanowires in the two temperature regions indicate the role of growth rate anisotropy and surface energy in dictating the ultimate nanomorphologies.     

Wires, plates, flowers, needles, and core-shells: diverse nanostructures of gold using polyaniline templates

A simple and versatile method for the synthesis of a wide range of polyaniline (PANI)-based 1D and 2D gold nanostructures of uniform size distribution with high colloidal stability is demonstrated. All the nanostructures were synthesized from oligoaniline-coated gold nanoparticle precursors. The nanostructures include nanowires of various sizes, nanoplates, and flower-like nanoparticles. These nanowires showed a pH-dependent shape transformation. Needle-like aggregates of Au/PANI were formed as the pH of the nanowire solution changed to 2.5. At higher pH (10.2), nanowires converted into spherical nanoparticles. Core-shell particles of Au/PANI composites have been achieved by the reversal of the pH of the nanowire from 10.2 to 2.9. The morphology of the nanostructures was studied by TEM and SEM. FTIR, UV-vis, XRD, and LDI MS were utilized for the characterization of the chemical composition of the nanostructures. A mechanism for the nanowire growth is proposed.