Abstract Bismuth compounds have generated much interest as agents for the removal of radioactive iodine. In this work, we present the shape‐controlled preparation of basic bismuth nitrate crystals (BBN) in the form of Reuleaux triangles, hexagons, and deformed hexagon disks. Shape control was achieved through modulation of the effect of the shape‐directing agent 2,3‐bis(2‐pyridyl)pyrazine (dpp). The crystals were shown to be capable of iodide removal through reaction with I − to form BiOI. Depending on the degree of saturation, the resultant solids can exhibit colors ranging from yellow (unsaturated) to orange (saturated). Sedimentation of the products facilitates its removal after use. While the removal capacities did not depend on the crystal morphology, the Reuleaux triangle disks exhibited faster reaction rates than the other two shapes. With improved removal capacities of up to 3.6 mmol g −1 , fast removal kinetics, good selectivity, and capture irreversibility, the BBN crystals show good potential as agents for radioactive iodine removal.
A facile and effective method to produce sub-10 nm Ag nanoparticles in a water solution is reported. Stabilization of the nanoparticles was achieved by hydrophobic interactions with the apolar primary faces of α-CD. In addition, hydrogen-bonding interactions between the exposed secondary -OH groups facilitated the threading of neighboring CDs, leading to the self-assembly of the Ag nanoparticles into 1-D "pearl necklace" arrays. The preparation of such metal nanoparticles unravels possibilities for the assembly of nanoparticles in 2- and 3-D patterns.
Recent research has established the influence of seed nature in determining the final shapes of metallic (Ag, Au) nanocrystals. In this work, we utilize and extend this knowledge to produce anisotropic β-AgI nanoplatelets in high yield: Ag seeds (∼20 nm) with twin defects were first selectively nucleated and then reacted with I- in a one-pot tandem reaction. I- performs multiple roles of oxidative dissolution regulator and reactant and surface stabilizing agent, thereby reducing the complexity of the synthesis. Examination of the nanocrystals at different stages of the reaction via electron microscopy confirmed that the AgI nanoplates grew from twinned Ag seeds and the initial Ag seed formation step was found to be vital to the appearance of the anisotropic platelike AgI nanocrystals. In general, the reaction of preformed metallic seeds with other reactive species may provide a convenient channel for the shape-controlled production of semiconductor nanostructures, with the final shapes being determined by the structure (twinning) of the seed. Aging of the reaction mixture in the presence of light resulted in the dissolution of AgI nanoplates to form Ag dendritic nanostructures. We explained its growth based on a diffusion-limited aggregation model.
The synthesis of Ag stellar dendrites was achieved using a solution-phase method by modeling the growth of stellar snowflakes. In the synthesis, 2,3-bis(2-pyridyl)pyrazine (dpp) acted as the growth-directing agent, forming hexagonal structures that served as the nuclei for the growth of stellar dendrites. Coupled with the careful control of experimental parameters to achieve a balance between reaction and diffusion rates, uniform and directional growth ensued, yielding symmetrical stellar dendrites represented by {111} facets. The influences of experimental conditions were investigated by analyzing the products formed under varied reaction and diffusion rates. The results were organized into an empirical chart that can serve as a visual reference to determine the experimental modifications required to prepare stellar dendrites. Time-dependence studies were carried out to elucidate the mechanism of growth into the unique dendritic patterns. SEM and HRTEM imaging of the intermediate structures revealed that the growth had occurred via oriented attachment of ∼10 nm Ag grains.
In the battle against radioactive material discharge, basic bismuth nitrate crystals in the form of Reuleaux triangles, deformed hexagons, and regular hexagon disks were tested for their ability to remove radioactive iodine in aqueous solutions. Shape control was achieved through modulation of the effect of the shape-directing agent 2,3-bis(2-pyridyl)pyrazine (dpp). More information can be found in the Full Paper by W. Y. Fan et al. on page 133 in Issue 2, 2016 (DOI: 10.1002/cnma.201500179).
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.
The study of metastable phases has been elusive due to their propensity to convert to the stable phase. In this work, 3-bis(2-pyridyl)pyrazine (dpp)-doping was successfully used to relieve the high pressures required for the formation of metastable α-Ag2MoO4. α-Ag2MoO4 spheres were prepared via solution-phase precipitation under ambient conditions with the addition of dpp. While the properties of β-Ag2MoO4 have been well-studied, the difficulty in preparing the α-phase has limited its investigations to theoretical calculations. The overdue synthesis of α-Ag2MoO4 allowed empirical snapshots of its electronic and optical properties. The spheres show absorption in the visible/near-IR regions, and the band gap was determined to be 1.26 eV. Unlike β-Ag2MoO4, which is known to decay into Ag filaments on electron irradiation, the α-Ag2MoO4 spheres maintain their structural and electronic integrity. The inclusion of dpp into the crystal lattice is used to explain the experimental observations.
We report a high-yield facile synthesis of uniform single-crystalline γ-CuI nanocrystals with tetrahedral morphology from the reaction between Cun and KI under ambient conditions. In our method, I- perform the roles of reactant and surface stabilizing agent, thereby reducing the complexity of the reaction by eliminating the need for an external capping agent. Nanotetrahedrons grow from single-crystalline seeds whose growth has been promoted by iodide-induced oxidative etching of twinned seeds. These nanocrystals have Td symmetry in which three triangular faces meet at each corner, and thus may be classified as platonic solids. Removal of excess free I- in solution initiates the dissolution of CuI nanotetrahedrons and simultaneous oxidation to CuO nanocages. Transmission electron microscopy was used to trace the hollowing process, and the nanoscale Kirkendall effect and other possible mechanisms were discussed for the formation of void interiors.
We report the shape evolution process of Cu2O 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 Cu2O 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 Cu2O nanooctahedrons was determined by the classical Tauc approach to be 2.24 eV, which is blue shifted with respect to the bulk Cu2O 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.
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.
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