Crystal overgrowth on gold nanorods: tuning the shape, facet, aspect ratio, and composition of the nanorods

Electrochemically prepared Au nanorods were used as seeds for the overgrowth of thin shells of gold, silver, and palladium by using a mild reducing agent, ascorbic acid, in the presence of surfactants at ambient condition. The unique crystal facets of the starting nanorods results in anisotropic crystal overgrowth. The overgrowth rates along different crystallographical directions can be further regulated by adding foreign ions or by using different metal reduction methods. This overgrowth study provides insights on how different metal ions could be reduced preferentially on different Au nanorod surfaces, so that the composition, aspect ratio, shape, and facet of the resulting nanostructures can be rationally tuned. These surfactant-stabilized bimetallic Au(core)M(shell) (M=Au, Ag, Pd) nanorod colloids might serve as better substrates in surface-enhanced Raman spectroscopy as well as exhibiting enhanced catalytic properties.     

Superstructures of Functional Colloids: Chemistry on the Nanometer Scale

Chemistry is classically concerned with the connection of atoms and molecules into new functional units. The rules of connection are yet to be extended to the generation and connection of larger objects, whose dimensions are measured in nanometers. However, linking objects of this size through molecules approaching each other randomly is inefficient, instead the principle of self-assembly is decisive, in which lyotropic structure formation or amphiphilic interaction play a significant role. As a result of the nature of the energetic driving forces, the objects generated in this way are often well-defined aggregate structures or highly symmetric volume phases. In contrast to “molecular chemistry”, the linking of larger objects also disregards the inherent borders of classical fields of chemistry: for example, the nanoscale association of inorganic colloids with polymers affords hybrid materials that combine the physical properties of both partners. In such a way, catalytic, optical, and electronic features of inorganic colloids might be combined with the mechanical characteristics of polymers such as film formation, elasticity, and melt processibility.     

Oriented attachment mechanism in anisotropic nanocrystals: a "polymerization" approach.

The kinetic model of stepwise polymerization is revisited, with some adaptations for its application to the kinetics of oriented attachment of nanoparticles in colloidal suspensions, which results in the formation of anisotropic particles. A comparison with experimental data reported in the literature shows good agreement with the model and supports comparisons with other systems.     

Linked crystallites in the conducting topmost layer of polymer bilayer films controlled by temperature: from micro- to nanocrystallites.

Temperature has great impact on the structure and size of the linked crystallites of the conducting topmost layer formed at the surface of a polycarbonate film via the reaction BEDT-TTF+IBr [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene]. We show that fine temperature control permits formation of a semiconducting topmost layer of alpha'-(BEDT-TTF)(2)(I(x)Br(1-x))(3) crystallites with either micro- or nanometre size, a result that opens a route to miniaturized conducting plastic materials.     

Orthogonal PbS nanowire arrays and networks and their Raman scattering behavior

Three-dimensional, orthogonal lead sulfide (PbS) nanowire arrays and networks have been prepared by using a simple, atmospheric pressure chemical vapor deposition (APCVD) method. These uniform nanowires (average diameter 30 nm) grow epitaxially from the surface of the initial PbS crystal seeds and form orthogonal arrays and networks in space. The growth mechanism has been explored, and the process was classified as homogeneous, epitaxial growth in the 200 directions. Furthermore, Raman spectra of PbS nanowires are reported here, and their characteristic Raman peak (190 cm(-1), no shoulder) could be used as a unique probe for the study of PbS nanomaterials.     

Microwave-induced formation of platinum nanostructured networks with superior electrochemical activity and stability

Platinum nanostructured networks (PNNs) can be synthesized through the chemical reduction of H(2)PtCl(6) by benzyl alcohol under microwave irradiation without the introduction of any surfactants, templates, or seeds. The synthesis route utilizes benzyl alcohol as both the reductant and the structure-directing agent, and thus, the process is particularly simple and highly repeatable. The formation of the PNN structure was ascribed to the collision-induced fusion of Pt nanocrystals owing to the cooperative functions of microwave irradiation and benzyl alcohol. Compared with a commercial Pt/C catalyst, the as-prepared PNNs possessed superior electrochemical activity and stability on the oxidation of methanol because of the unique 3D nanostructured networks and abundant defects formed during the assembly process. This study may provide a facile microwave-induced approach for the synthesis of other 3D nanostructured noble metals or their alloys.     

Shape- and phase-controlled synthesis of monodisperse, single-crystalline ternary chalcogenide colloids through a convenient solution synthesis strategy

Colloidal, monodisperse, single-crystalline pyramidal CuInS2 and rectangular AgInS2 nanocrystals were successfully synthesized through a convenient and improved solvothermal process that uses hexadecylamine as a capping reagent. The crystal phase, morphology, crystal lattice, and chemical composition of the as-prepared products were characterized by using X-ray diffraction, transmission electron microscopy (TEM), high-resolution TEM, and energy dispersive X-ray spectroscopy. Results revealed that the as-synthesized CuInS2 colloid is in the tetragonal phase (size: 13-17 nm) and the AgInS2 in the orthorhombic structure (size: 17+/-0.5 nm). A possible shape evolution and crystal growth mechanism has been suggested for the formation of pyramidal CuInS2 and rectangular AgInS2 colloids. Control experiments indicated that the morphology- and/or phase-change of CuInS2 and orthorhombic AgInS2 colloids are temperature- and/or time-dependent. CuInS2 colloids absorb well in the range of visible light at room-temperature, indicating its potential application as a solar absorber. Two photoluminescence (PL) subbands at 1.938 and 2.384 eV in the PL spectra of CuInS2 colloids revealed that the recombination of the closest and the second closest donor-acceptor pairs within the CuInS2 lattice, in which the donor defect (Cui) occupies an interstitial position and the acceptor defect (VIn) resides at an adjacent cation site. In addition, the synthesis strategy developed in this study is convenient and inexpensive, and could also be used as a general process for the synthesis of other pure or doped ternary chalcogenides that require a controlled size (or shape). This process could be extended to the synthesis of other functional nanomaterials.     

Synthesis of Hierarchical Macro‐/Mesoporous Solid‐Solution Photocatalysts by a Polymerization–Carbonization–Oxidation Route: The Case of Ce0.49Zr0.37Bi0.14O1.93

A hierarchical macro‐/mesoporous Ce_0.49Zr_0.37Bi_0.14O_1.93 solid‐solution network has been synthesized on a large scale by means of a simple and general polymerization–carbonization–oxidation synthetic route. The as‐prepared product has been characterized by SEM, XRD, TEM, BET surface area measurement, UV/Vis diffuse‐reflectance spectroscopy, energy‐dispersive X‐ray spectroscopy (EDS), and photoelectrochemistry measurements. The photocatalytic activity of the product has been demonstrated through the photocatalytic degradation of methyl orange. Structural characterization has indicated that the hierarchical macro‐/mesoporous solid‐solution network not only contains numerous macropores, but also possesses an interior mesoporous structure. The mesopore size and BET surface area of the network have been measured as 2–25 nm and 140.5 m² g^?1, respectively. The hierarchical macro‐/mesoporous solid‐solution network with open and accessible pores was found to be well‐preserved after calcination at 800 °C, indicating especially high thermal stability. Due to its high specific surface area, the synergistic effect of the coupling of macropores and mesopores, and its high crystallinity, the Ce_0.49Zr_0.37Bi_0.14O_1.93 solid‐solution material shows a strong structure‐induced enhancement of visible‐light harvest and exhibits significantly improved visible‐light photocatalytic activity in the photodegradation of methyl orange compared with those of its other forms, such as mesoporous hollow spheres and bulk particles.     

Synthesis of monolayer-patched graphene from glucose

Graphene patchwork: A simple synthetic process requiring neither catalyst nor solvent was used to convert glucose directly into polycrystalline carbon sheets having a "patched" multidomain graphene structure with domains 2-15?nm in size. The carbon assemblies exhibit high conductivity, high specific surface area, and an unexpectedly good solution processability.     

The Generation of an Organic Inverted Chemical Garden

A chemical garden based on iron salt that grows in organic solvents and ions is demonstrated for the first time. This prototype chemical garden develops in an inverted orientation, thus providing evidence that downward growth is feasible.     

Early stages of ZnS nanoparticle growth studied by in-situ stopped-flow UV absorption spectroscopy.

The early stages of ZnS nanoparticle growth from supersaturated solution are investigated in situ by stopped-flow UV absorption spectroscopy with a time resolution of 1.28 ms. A model for data analysis is suggested which makes it possible to study both the average particle radius and the concentration. The average radii lie in the sub-nanometer range. During the first 40 ms, growth is predominantly governed by ripening.