A remote-controlled generation of gold@polydopamine (core@shell) nanoparticles via physical-chemical stimuli of polydopamine/gold composites.

We present the synthesis of polydopamine particle-gold composites (PdopP-Au) and unique release of Au@Pdop core@shell nanoparticles (NPs) from the PdopP-Au upon external stimuli. The PdopP-Au was prepared by controlled synthesis of AuNPs on the Pdop particles. Upon near infrared (NIR) irradiation or NaBH4 treatment on the PdopP-Au, the synthesized AuNPs within the PdopPs could be burst-released as a form of Au@Pdop NPs. The PdopP-Au composite showed outstanding photothermal conversion ability under NIR irradiation due to the ultrahigh loading of the AuNPs within the PdopPs, leading to a remote-controlled explosion of the PdopP-Au and rapid formation of numerous Au@Pdop NPs. The release of the Au@Pdop NPs could be instantly stopped or re-started by off or reboot of NIR, respectively. The structure of the released Au@Pdop NPs is suitable for a catalyst or adsorbent, thus we demonstrated that the PdopP-Au composite exhibited excellent and sustained performances for environmental remediation due to its capability of the continuous production of fresh catalysts or adsorbents during the reuse.

Defect-mediated modulation of optical properties in vertically aligned ZnO nanowires via substrate-assisted Ga incorporation.

We report the defect-mediated modulation of optical properties in vertically aligned ZnO nanowires via a substrate-assisted Ga incorporation method. We find that Ga atoms were incorporated into a ZnO lattice via the diffusion of liquid Ga droplets from a GaAs substrate in which as-grown ZnO nanowires were placed face down on the GaAs substrate and annealed at 650 °C. Based on structural and compositional characterization, it was confirmed that the substrate-assisted incorporation of Ga can induce a high defect density in vertically aligned ZnO nanowires grown on a Si substrate. In addition, distinct differences in optical properties between as-grown and Ga-incorporated ZnO nanowires were found and discussed in terms of defect-mediated modifications of energy band states, which were associated with the generation and recombination of photoexcited carriers. Furthermore, it was clearly observed that for Ga-incorporated ZnO nanowires, the photocurrent rise and decay processes were slower and the photocurrents under UV illumination were significantly higher compared with as-grown nanowires.

Rattle-type hierarchical particles containing multilevel cores (Ag@AgCl@SiO2 and Au/Ag@AgCl@SiO2) as versatile catalysts.

A protocol for the synthesis of rattle-type core@shell particles containing Ag@AgCl or Au/Ag@AgCl core structures was developed, and the use of these particles as catalysts for the decomposition of toxic materials was demonstrated. A monometallic Ag or bimetallic Au/Ag core was incorporated into the interior of SiO2 capsules via controlled heat treatment of metal nanoparticle/SiO2-coated polymer particles, resulting in the formation of rattle-type core@shell structures. By appropriate treatments, it was possible to transform the Ag or Au/Ag core into multilevel cores (Ag@AgCl or Au/Ag@AgCl) within the SiO2 capsules (Ag@AgCl@SiO2 or Au/Ag@AgCl@SiO2). This method for the synthesis of rattle-type core@shell particles is useful for further introducing AgCl fused with plasmonic materials into the capsule structures. The rattle-type core@shell structures were used as photocatalysts for the decomposition of organic pollutants such as methyl orange. Furthermore, these nanocatalysts containing semiconductors such as AgCl were also applied toward the reduction of nitrophenol (NPh) to aminophenol (APh). The Ag@AgCl@SiO2 or Au/Ag@AgCl@SiO2 catalysts showed excellent catalytic properties in the decomposition of toxic substances in terms of their activity and reusability.

Sea-urchin-like iron oxide nanostructures for water treatment.

To obtain adsorbents with high capacities for removing heavy metals and organic pollutants capable of quick magnetic separation, we fabricated unique sea-urchin-like magnetic iron oxide (mixed γ-Fe2O3/Fe3O4 phase) nanostructures (called u-MFN) with large surface areas (94.1m(2) g(-1)) and strong magnetic properties (57.9 emu g(-1)) using a simple growth process and investigated their potential applications in water treatment. The u-MFN had excellent removal capabilities for the heavy metals As(V) (39.6 mg g(-1)) and Cr(VI) (35.0 mg g(-1)) and the organic pollutant Congo red (109.2 mg g(-1)). The u-MFN also displays excellent adsorption of Congo red after recycling. Because of its high adsorption capacity, fast adsorption rate, and quick magnetic separation from treated water, the u-MFN developed in the present study is expected to be an efficient magnetic adsorbent for heavy metals and organic pollutants in aqueous solutions.

Hierarchical hollow spheres of Fe2O3 @polyaniline for lithium ion battery anodes.

Hierarchical hollow spheres of Fe2 O3 @polyaniline are fabricated by template-free synthesis of iron oxides followed by a post in- and exterior construction. A combination of large surface area with porous structure, fast ion/electron transport, and mechanical integrity renders this material attractive as a lithium-ion anode, showing superior rate capability and cycling performance.

Rapid two-step metallization through physicochemical conversion of Ag2O for printed "black" transparent conductive films.

A rapid two-step metallization for fabrication of a "black" transparent conductive film on a flexible substrate for display applications is presented, using a mixture of silver oxide (Ag2O) and silver neodecanoate (C10H19AgO2), and its electrical conductivity and colour transition behaviours are investigated. Silver nanoparticles, which are physicochemically converted from silver oxide microparticles in the presence of silver neodecanoate in the course of the first metallization step at 150 °C for 10 min, are chemically annealed by immersing them in an acidic ferric chloride (FeCl3) solution at room temperature for 10 s. During this second metallization step, silver nanoparticles are found to be tightly packed through Ostwald ripening, which eventually leads to the dramatic enhancement of electrical conductivity by six orders of magnitude from 1.33 S m(-1) to 1.0 × 10(7) S m(-1), which corresponds to 15.9% of the electrical conductivity of bulk silver. In addition to the enhancement of electrical conductivity, the silver chloride (AgCl) layer formed on the surface of the silver layer due to ferric ions (Fe(3+)) enhances the blackness of the transparent conductive film by a factor of 1.69, from 36.29 B to 61.51 B. The sheet resistance and optical transparency of a roll-to-roll printed black transparent conductive film for a touch screen panel are found to be as low as 0.9 Ω□(-1) and 81%, respectively, after conducting the proposed two-step metallization.

Hydrogen-induced morphotropic phase transformation of single-crystalline vanadium dioxide nanobeams.

We report a morphotropic phase transformation in vanadium dioxide (VO2) nanobeams annealed in a high-pressure hydrogen gas, which leads to the stabilization of metallic phases. Structural analyses show that the annealed VO2 nanobeams are hexagonal-close-packed structures with roughened surfaces at room temperature, unlike as-grown VO2 nanobeams with the monoclinic structure and with clean surfaces. Quantitative chemical examination reveals that the hydrogen significantly reduces oxygen in the nanobeams with characteristic nonlinear reduction kinetics which depend on the annealing time. Surprisingly, the work function and the electrical resistance of the reduced nanobeams follow a similar trend to the compositional variation due mainly to the oxygen-deficiency-related defects formed at the roughened surfaces. The electronic transport characteristics indicate that the reduced nanobeams are metallic over a large range of temperatures (room temperature to 383 K). Our results demonstrate the interplay between oxygen deficiency and structural/electronic phase transitions, with implications for engineering electronic properties in vanadium oxide systems.

Formation of CuInSe2 absorber layers formed using co-electrodeposition combined with selenization.

Stoichiometric CuInSe2 absorber layers were formed using co-electrodeposition coupled with selenization. We investigated the influence of the metal ion ratio, supporting electrolyte, and deposition voltages on the structural and chemical properties of Cu-In alloys. The increases in deposition voltage and metal ion concentration helped to form In-rich Cu-In alloy with dendrite structure composed of a long central trunk with secondary branches. In addition, on increasing the concentration of the supporting electrolyte, the ratio of In to Cu in the Cu-In alloy increased, and surface morphology improved. Finally, based on an optimized co-electrodeposition process, the selenization of Cu-In alloys using the evaporation of the Se element was employed to form high quality CuInSe2 absorber layers.

3D heterostructured architectures of Co3O4 nanoparticles deposited on porous graphene surfaces for high performance of lithium ion batteries.

Control of structure and morphology in electrode design is crucial for creating efficient transport pathways of ions and electrons in high-performance energy storage devices. Here we report the fabrication of high-performance anode materials for lithium-ion batteries based on a 3D heterostructured architecture consisting of Co(3)O(4) nanoparticles deposited onto porous graphene surfaces. A combination of replication and filtration processes - a simple and general method - allows a direct assembly of 2D graphene sheets into 3D porous films with large surface area, porosity, and mechanical stability. The polystyrene spheres are employed as sacrificial templates for an embossing technique that yields porous structures with tunable pore sizes ranging from 100 nm to 2 µm. Co(3)O(4) nanoparticles with high-energy storage capacity can be easily incorporated into the pore surfaces by a simple deposition strategy, thereby creating a 3D heterogeneous Co(3)O(4)/graphene film. In particular, we exploit the 3D Co(3)O(4)/graphene composite films as anode materials for lithium ion batteries in order to resolve the current issues of rate capability and cycling life. This unique heterogeneous 3D structure is capable of delivering excellent Li(+) ion storage/release and displays the following characteristics: a high rate capability of 71% retention even at a high current rate of 1000 mA g(-1) and a good cycling performance with 90.6% retention during 50 cycles. The versatile and simple nature of preparing 3D heterogeneous graphene films with various functional nanoparticles can be extended to overcome the major challenges that exist for many electrochemical devices.

Production of graphene by exfoliation of graphite in a volatile organic solvent.

The production of unfunctionalized and nonoxidized graphene by exfoliation of graphite in a volatile solvent, 1-propanol, is reported. A stable homogeneous dispersion of graphene was obtained by mild sonication of graphite powder and subsequent centrifugation. The presence of a graphene monolayer was observed by atomic force microscopy and transmission electron microscopy. The solvent, 1-propanol, from the deposited dispersion was simply and quickly removed by air drying at room temperature, without the help of high temperature annealing or vacuum drying, which shortens production time and does not leave any residue of the solvent in the graphene sheets.

Graphene-based multifunctional iron oxide nanosheets with tunable properties.

We report the synthesis of graphenes with tunable properties due to the growth of needlelike iron oxide (IO) nanoparticles on their surfaces. The electrical conductivity, flexibility, and magnetic properties of graphene nanosheets (GNSs) could be tuned on demand by fine controlling both the surface coverage and the length of the IO nanoneedles. The degree of coverage of the IO nanoparticles on the surface of the GNSs made it possible to control the resulting properties of the IO/GNSs on demand. As examples of their utility, paperlike materials were generated by simple filtration, and the resulting IO/GNS nanocomposites showed extraordinary removal capacity and fast adsorption rates for As(V) and Cr(VI) ions in water. Another possible application is the preparation of multifunctional films equipped with conductivity, flexibility, and magnetic properties. The fabrication process is easy to scale up at a low cost. In addition, both the colloidal solution and film forms of the resulting IO/GNSs were effective for removal of heavy metal ions, meaning this material could be utilized for actual industrial applications.

Single-walled hollow nanospheres assembled from the aluminogermanate precursors.

Ordered single-walled hollow aluminogermanate (ALGE) nanospheres (NSs) with average monodisperse diameters of 5 nm have been synthesized for the first time using simple pH control. This involved basification of the ALGE precursors (having an Al/Ge ratio of 1.33) to a pH value of 13, followed by immediate acidification to a pH value of 9.

Quantitative assessment of nanoparticle single crystallinity: palladium-catalyzed splitting of polycrystalline metal oxide nanoparticles.

Crystal gazing: A simple Pd-catalyzed site-specific nanoetching method was developed to visualize the polycrystalline nature of Fe(3)O(4) (see picture), Fe(2)O(3), MnFe(2)O(4), CoFe(2)O(4), and MnO nanoparticle systems. The technique relies on the very fast etching speed of the grain interface within bi- or polycrystalline nanocrystals.