Reuleaux triangle disks: new shape on the block.

We report here the unprecedented preparation of Reuleaux triangle disks. The hydrolysis and precipitation of bismuth nitrate in an ethanol-water system with 2,3-bis(2-pyridyl)pyrazine yielded basic bismuth nitrate Reuleaux triangle disks. Analysis of the intermediates provided insights into the mystery behind the formation of the Reuleaux triangle disk, revealing a unique growth process. The report of a facile method to prepare crystals of a novel shape in high yield, with good homogeneity, and with excellent reproducibility is expected to unlock new research directions in multiple disciplines.

Colloidal beading: sonication-induced stringing of selenium particles.

We report the preparation of monodispersed Se colloidal aggregates (dimers and trimers) via sonication-induced aggregation of spherical monomers. Control over the size and morphology of the products was achieved by changing the aging and sonication times, respectively. The possible mechanisms for the formation of colloidal aggregates were discussed. This method can provide a simple and versatile approach to the production of colloidal molecules of particles composed of different materials, which will be useful for fundamental studies related to colloidal systems.

Formation of Ag2Se nanotubes and dendrite-like structures from UV irradiation of a CSe2/Ag colloidal solution.

Ag2Se nanotubes have been successfully synthesized by UV photodissociation of adsorbed CSe2 on the surface of Ag nanowires under ambient conditions. Transmission electron microscopy was used to trace the growth of hollow interiors, allowing a detail study of the Kirkendall effect in 1-dimensional nanosystems. Voids were observed to grow from both ends of the nanowires along the longitudinal axis and ultimately merged to form hollow nanotubes. This phenomenon is attributed to the crystallographic selective adsorption of poly(vinylpyrolidone) on Ag nanowire templates. In addition, we observed the formation of dendrites on aging of the reaction mixture and explained its growth based on a diffusion-limited aggregation model.

Shape evolution of Cu2O nanostructures via kinetic and thermodynamic controlled growth.

We report the shape evolution process of Cu(2)O nanocrystals upon slow oxidation of Cu under ambient conditions, yielding novel hexagonal and triangular platelike morphologies. The shape of the obtained nanocrystals evolves from hexagonal to triangular to octahedral; the growth patterns are governed by kinetically and thermodynamically controlled growth. Preferential adsorption of I(-) on {111} planes of Cu(2)O nanoparticles induced the selective crystal growth of metastable platelike structures with {111} faces as the basal planes. On aging, the growth process appeared to shift into the thermodynamic regime and the thermodynamically stable octahedral shape is obtained. The possible growth mechanisms were investigated by varying the synthetic conditions. The band gap of Cu(2)O nanooctahedrons was determined by the classical Tauc approach to be 2.24 eV, which is blue shifted with respect to the bulk Cu(2)O value (2.17 eV). Results suggest that the slow oxidation process and use of crystallographic selective surfactants are essential for the appearance of anisotropic metastable shapes. In general, surface energy control by surfactant molecules might provide a convenient channel for tailoring nanocrystal shapes of metal oxides.