RESUMEN
Excavated polyhedral noble-metal materials that were built by the orderly assembly of ultrathin nanosheets have both large surface areas and well-defined facets, and therefore could be promising candidates for diverse important applications. In this work, excavated cubic Pt-Sn alloy nanocrystals (NCs) with {110} facets were constructed from twelve nanosheets by a simple co-reduction method with the assistance of the surface regulator polyvinylpyrrolidone. The specific surface area of the excavated cubic Pt-Sn NCs is comparable to that of commercial Pt black despite their larger particle size. The excavated cubic Pt-Sn NCs exhibited superior electrocatalytic activity in terms of both the specific area current density and the mass current density towards methanol oxidation.
RESUMEN
The intrinsic factors affecting the bulk structures of nanocrystallites are not well explored during crystallization. In this study, it is demonstrated that the chemical potential of growth units plays decisive role in governing the final structure of nanocrystals. It is found that the types of reaction vessels are able to vary the chemical potential of growth units, and make the Pt and Pd nanocrystals (NCs) unexpectedly evolve from the cyclic penta-twinned to the single-crystal nanostructures. In turn, it is concluded that the crystal growth units with lower chemical potential favor the formation of crystal nuclei with lower chemical potential during the nucleation. This new approach in tuning the bulk structures of NCs enriches the understanding of the crystallization process under supersaturated (nonequilibrium) condition, and would provide a general guidance for controlling nanocrystals with various thermodynamic forms.
RESUMEN
Concave morphologies provide noble metal nanocrystals (NCs) with unique performances due to large specific surface areas, high curves, hot spots, and elevated energy facets. As a result, concave morphologies have attracted considerable attention in many areas. However, most NCs with concave shapes are currently made of a single metal, leaving plenty of room for easy wet chemical synthesis and structural analysis of unique concave structures, especially bimetallic compounds. In this work, concave octahedral Pt-Pd alloy NCs with high-index {hhl} faces were synthesized using glycine as a coordination molecule and polyvinylpyrrolidone as the surfactant and reducing agent. The high-index facets coupled with the synergistic and electronic effects between Pt and Pd provided concave octahedral Pt-Pd alloy NCs with excellent activity and stability toward the electrooxidation of formic acid when compared to their convex counterparts and commercial Pt black.
RESUMEN
By combining the fluorophores of axially chiral 1,1'-binaphthol (BINOL) and 1,4-dihydropyridine derivatives, axially chiral 1,4-dihydropyridine derivatives ((R)-/(S)-2) with aggregation-induced emission (AIE) in exciplexes were designed and synthesized. (R)-/(S)-2 emitted low fluorescence in THF solutions of their locally excited states; however, they emitted red-shifted fluorescence in the aggregate state upon exciplex formation. Moreover, (R)-/(S)-2 showed linear and multi-exponential relationships between their local excited and exciplex fluorescence intensities and the viscosity of the medium, which allowed us to determine the viscosities of different mixed solvents. In addition, as an axially chiral viscosity probe, (R)-/(S)-2 show excellent CD signals and have potential applications in the fields of chiral recognition and fluorescence imaging, which will broaden the new family of AIE fluorophores. To the best of our knowledge, there are few reports of axially chiral intramolecular exciplex-mediated AIE molecules.
RESUMEN
Icosahedra have small contact areas during packing, leading small icosahedral Pt nanoparticles to highly disperse on carbon nanotubes (CNT). The as-synthesized highly monodispersed Pt icosahedra on CNT exhibited superior catalytic activity and structural stability to their Pt nanocube counterparts on CNT towards methanol electro-oxidation.
RESUMEN
Seed-mediated growth is the most general way to controllably synthesize bimetal nano-heterostructures. Despite successful instances through trial and error were reported, the way for second metal depositing on the seed, namely whether the symmetry of resulted nano-heterostructure follows the original crystal symmetry of seed metal, remains an unpredictable issue to date. In this work, we propose that the thermodynamic factor, i.e., the difference of equilibrium electrochemical potentials (corresponding to their Fermi levels) of two metals in the growth solution, plays a key role for the symmetry breaking of bimetal nano-heterostructures during the seed-mediated growth. As a proof-of-principle experiment, by reversing the relative position of Fermi levels of the Pd nanocube seeds and the second metal Au with changing the concentration of reductant (L-ascorbic acid) in the growth solution, the structure of as-prepared products successfully evolved from centrosymmetric Pd@Au core-shell trisoctahedra to asymmetric Pd-Au hetero-dimers. The idea was further demonstrated by the growth of Ag on the Pd seeds. The present work intends to reveal the origin of symmetry breaking in the seed-mediated growth of nano-heterostructures from the viewpoint of thermodynamics, and these new insights will in turn help to achieve rational construction of bimetal nano-heterostructures with specific functions.
RESUMEN
In wet chemical syntheses of noble metal nanocrystals, surfactants play crucial roles in regulating their morphology. To date, more attention has been paid to the effect of the surfactant on the surface energy of crystal facets, while less attention has been paid to its effect on the growth kinetics. In this paper, using the growth of Au-Pd alloy nanocrystals as an example, we demonstrate that different concentration of surfactant hexadecyltrimethyl ammonium chloride (CTAC) may cause the different packing density of CTA+ bilayers on different sites (face, edge or vertex) of crystallite surface, which would change the crystal growth kinetics and result in preferential crystal growth along the edge or vertex of crystallites. The unique shape evolution from trisoctahedron to excavated rhombic dodecahedron and multipod structure for Au-Pd alloy nanocrystals was successfully achieved by simply adjusting the concentration of CTAC. These results help to understand the effect of surfactants on the shape evolution of nanocrystals and open up avenues to the rational synthesis of nanocrystals with the thermodynamically unfavorable morphologies.
RESUMEN
A simple strategy for the direct and indirect detections of bisphenol A (BPA) at an ITO electrode is described. The direct determination of BPA in buffer solution of pH 7.2 is accomplished by the application of differential pulse voltammograms with the anodic peak at 0.546 V. The indirect approach is based on the mediation of [Ru(bpy)(3)](2+) (where bpy=2,2'-bipyridine), which is served as an excellent catalyst to induce the oxidation of BPA. By monitoring the peak current of [Ru(bpy)(3)](2+)-BPA complex, the mediated detection of BPA is successfully carried out. The response current exhibits a linear range between 5 and 120 micromol L(-1) with a high sensitivity (0.22 microA micromol(-1) L). The detection limit of BPA is 0.29 micromol L(-1) (S/N=3), which is larger than that analyzed by gas chromatography-mass spectrometry, however this detection method not only has the advantages of low cost and simple operation, but also provides a powerful basis for removing BPA. In addition, according to the effects of pH, scan rate and mediator concentrations on the voltammetric responses of BPA oxidation, the oxidized mechanism of BPA in the presence of [Ru(bpy)(3)](2+) on the ITO electrode is discussed in detail.