25 research outputs found
Synthesis of Single-Crystalline Lead Sulfide Nanoframes and Nanorings
We present a colloidal synthesis strategy to obtain single-crystalline PbS nanorings. By controlling the ripening process in the presence of halide ions, a transformation of initial PbS nanosheets to framelike structures and finally to nanorings was achieved. We found that the competing ligands oleic acid, oleate, and halide ions play an important role in the formation of these nanostructures. Therefore, we propose a formation mechanism based on a thermally induced ripening of crystal facets dependent on the surface passivation. With this method, it became possible to synthesize colloidal nanorings of cubic crystal phase galena PbS. The synthesis was followed via TEM, and the products are characterized by XRD, AFM, and STEM tomography. Control of the initial nanoframe morphology allows adjusting the later nanoring dimensions
Colloidal lead iodide nanorings
Colloidal chemistry of nanomaterials experienced a tremendous development in
the last decades. In the course of the journey 0D nanoparticles, 1D nanowires,
and 2D nanosheets have been synthesized. They have in common to possess a
simple topology. We present a colloidal synthesis strategy for lead iodide
nanorings, with a non-trivial topology. First, two-dimensional structures were
synthesized in nonanoic acid as the sole solvent. Subsequently, they underwent
an etching process in the presence of trioctylphosphine, which determines the
size of the hole in the ring structure. We propose a mechanism for the
formation of lead iodide nanosheets which also explains the etching of the
two-dimensional structures starting from the inside, leading to nanorings. In
addition, we demonstrate a possible application of the as-prepared nanorings in
photodetectors. These devices are characterized by a fast response, high gain
values, and a linear relation between photocurrent and incident light power
intensity over a large range. The synthesis approach allows for inexpensive
large-scale production of nanorings with tunable properties.Comment: 26 pages, 7 figures, 2 scheme
Function Follows Form: From Semiconducting to Metallic toward Superconducting PbS Nanowires by Faceting the Crystal
In the realm of colloidal nanostructures, with its immense capacity for shape
and dimensionality control, the form is undoubtedly a driving factor for the
tunability of optical and electrical properties in semiconducting or metallic
materials. However, influencing the fundamental properties is still challenging
and requires sophisticated surface or dimensionality manipulation. In this
work, we present such a modification for the example of colloidal lead sulphide
nanowires. We show that the electrical properties of lead sulphide
nanostructures can be altered from semiconducting to metallic with indications
of superconductivity, by exploiting the flexibility of the colloidal synthesis
to sculpt the crystal and to form different surface facets. A particular
morphology of lead sulphide nanowires has been synthesized through the
formation of {111} surface facets, which shows metallic and superconducting
properties in contrast to other forms of this semiconducting crystal, which
contain other surface facets ({100} and {110}). This effect, which has been
investigated with several experimental and theoretical approaches, is
attributed to the presence of lead rich {111} facets. The insights promote new
strategies for tuning the properties of crystals as well as new applications
for lead sulphide nanostructures.Comment: 23 pages, 6 figure
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Improved CO oxidation activity in the presence and absence of hydrogen over cluster-derived PtFe/SiO2 catalysts
Low-Lanthanide-Content CeO2/MgO Catalysts with Outstandingly Stable Oxygen Storage Capacities: An In-Depth Structural Characterization by Advanced STEM Techniques
International audienceA novel CeO2/MgO catalyst with low ceria loading has been synthesized. This catalyst showed unique redox properties compared with conventional high and low surface area CeO2. Advanced (scanning) transmission electron microscopy techniques revealed the presence of a variety of highly dispersed ceria nanostructures: isolated CeOx entities, CeO2 clusters, as well as fairly small (<5nm) CeO2 nanoparticles. More interestingly, this CeO2/MgO catalyst showed outstanding stability in its redox response against high temperature aging treatments. Thus, after reduction in hydrogen at 950 degrees C and further oxidation at 500 degrees C, CeO2 reduction effects took still place at low temperatures, and no significant loss of oxygen storage capacity (OSC) was detected. Unique ceria-bilayer nanostructures were found and characterized in the aged catalyst. Their peculiar structural and chemical properties seem to be responsible for the large improvement observed in the stability of the redox response
Improved Oxidase Mimetic Activity by Praseodymium Incorporation into Ceria Nanocubes
Ceria
nanocubes (NC) modified with increasing concentrations of praseodymium
(5, 10, 15, and 20 mol %) have been successfully synthesized by a
hydrothermal method. The as-synthesized Pr-modified ceria nanocubes
exhibit an enhanced oxidase-like activity on the organic dye TMB within
a wide range of concentrations and durations. The oxidase activity
increases with increasing Pr amounts in Pr-modified ceria nanocubes
within the investigated concentration range. Meanwhile, these Pr-modified
ceria nanocubes also show higher reducibility than pure ceria nanocubes.
The kinetics of their oxidase mimetic activity is fitted with the
Michaelis–Menten equation. A mechanism has been proposed on
how the Pr incorporation could affect the energy level of the bands
in ceria and hence facilitate the TMB oxidation reaction. The presence
of Pr<sup>3+</sup> species on the surface also contributes to the
increasing activity of the Pr-modified ceria nanocubes present higher
oxidase activity than pure ceria nanocubes