15 research outputs found
Influence of the Ion Coordination Number on Cation Exchange Reactions with Copper Telluride Nanocrystals
Cu2-xTe nanocubes were used as starting seeds to access metal telluride
nanocrystals by cation exchanges at room temperature. The coordination number
of the entering cations was found to play an important role in dictating the
reaction pathways. The exchanges with tetrahedrally coordinated cations (i.e.
with coordination number 4), such as Cd2+ or Hg2+, yielded monocrystalline CdTe
or HgTe nanocrystals with Cu2-xTe/CdTe or Cu2-xTe/HgTe Janus-like
heterostructures as intermediates. The formation of Janus-like architectures
was attributed to the high diffusion rate of the relatively small tetrahedrally
coordinated cations, which could rapidly diffuse in the Cu2-xTe NCs and
nucleate the CdTe (or HgTe) phase in a preferred region of the host structure.
Also, with both Cd2+ and Hg2+ ions the exchange led to wurtzite CdTe and HgTe
phases rather than the more stable zinc-blende ones, indicating that the anion
framework of the starting Cu2- xTe particles could be more easily deformed to
match the anion framework of the metastable wurtzite structures. As hexagonal
HgTe had never been reported to date, this represents another case of
metastable new phases that can only be accessed by cation exchange. On the
other hand, the exchanges involving octahedrally coordinated ions (i.e. with
coordination number 6), such as Pb2+ or Sn2+, yielded rock-salt polycrystalline
PbTe or SnTe nanocrystals with Cu2-xTe@PbTe or Cu2-xTe@SnTe core@shell
architectures at the early stages of the exchange process. In this case, the
octahedrally coordinated ions are probably too large to diffuse easily through
the Cu2-xTe structure: their limited diffusion rate restricts their initial
reaction to the surface of the nanocrystals, where cation exchange is initiated
unselectively, leading to core@shell architectures.Comment: 11 pages, 7 figures in J. Am. Chem. Soc, 13 May 201
Ab Initio Structure Determination of Cu2- xTe Plasmonic Nanocrystals by Precession-Assisted Electron Diffraction Tomography and HAADF-STEM Imaging
We investigated pseudo-cubic CuTe nanosheets using electron diffraction tomography and high-resolution HAADF-STEM imaging. The structure of this metastable nanomaterial, which has a strong localized surface plasmon resonance in the near-infrared region, was determined ab initio by 3D electron diffraction data recorded in low-dose nanobeam precession mode, using a new generation background-free single-electron detector. The presence of two different, crystallographically defined modulations creates a 3D connected vacancy channel system, which may account for the strong plasmonic response of this material. Moreover, a pervasive rotational twinning is observed for nanosheets as thin as 40 nm, resulting in a tetragonal pseudo-symmetry
Ab Initio Structure Determination of Cu2- xTe Plasmonic Nanocrystals by Precession-Assisted Electron Diffraction Tomography and HAADF-STEM Imaging
We investigated pseudo-cubic Cu2-xTe nanosheets using electron diffraction tomography and high-resolution HAADF-STEM imaging. The structure of this metastable nanomaterial, which has a strong localized surface plasmon resonance in the near-infrared region, was determined ab initio by 3D electron diffraction data recorded in low-dose nanobeam precession mode, using a new generation background-free single-electron detector. The presence of two different, crystallographically defined modulations creates a 3D connected vacancy channel system, which may account for the strong plasmonic response of this material. Moreover, a pervasive rotational twinning is observed for nanosheets as thin as 40 nm, resulting in a tetragonal pseudo-symmetry
Nanoscale Transformations in Covellite (CuS) Nanocrystals in the Presence of Divalent Metal Cations in a Mild Reducing Environment
We studied the structural and compositional transformations of colloidal covellite (CuS) nanocrystals (and of djurleite (Cu1.94S) nanocrystals as a control) when exposed to divalent cations, as Cd2+ and Hg2+, at room temperature in organic solvents. All the experiments were run in the absence of phosphines, which are a necessary ingredient for cation exchange reactions involving copper chalcogenides, as they strongly bind to the expelled Cu+ ions. Under these experimental conditions, no remarkable reactivity was indeed seen for both CuS and Cu1.94S nanocrystals. On the other hand, in the covellite structure 2/3 of sulfur atoms form covalent S–S bonds. This peculiarity suggests that the combined presence of electron donors and of foreign metal cations can trigger the entry of both electrons and cations in the covellite lattice, causing reorganization of the anion framework due to the rupture of the S–S bonds. In Cu1.94S, which lacks S–S bonds, this mechanism should not be accessible. This hypothesis was proven by the experimental evidence that adding ascorbic acid increased the fraction of metal ions incorporated in the covellite nanocrystals, while it had no noticeable effect on the Cu1.94S ones. Once inside the covellite particles, Cd2+ and Hg2+ cations engaged in exchange reactions, pushing the expelled Cu+ ions toward the not-yet exchanged regions in the same particles, or out to the solution, from where they could be recaptured by other covellite nanoparticles/domains. Because no good solvating agent for Cu ions was present in solution, they essentially remained in the nanocrystals.ISSN:0897-475
Nanoscale Transformations in Covellite (CuS) Nanocrystals in the Presence of Divalent Metal Cations in a Mild Reducing Environment
We
studied the structural and compositional transformations of
colloidal covellite (CuS) nanocrystals (and of djurleite (Cu<sub>1.94</sub>S) nanocrystals as a control) when exposed to divalent cations, as
Cd<sup>2+</sup> and Hg<sup>2+</sup>, at room temperature in organic
solvents. All the experiments were run in the absence of phosphines,
which are a necessary ingredient for cation exchange reactions involving
copper chalcogenides, as they strongly bind to the expelled Cu<sup>+</sup> ions. Under these experimental conditions, no remarkable
reactivity was indeed seen for both CuS and Cu<sub>1.94</sub>S nanocrystals.
On the other hand, in the covellite structure 2/3 of sulfur atoms
form covalent S–S bonds. This peculiarity suggests that the
combined presence of electron donors and of foreign metal cations
can trigger the entry of both electrons and cations in the covellite
lattice, causing reorganization of the anion framework due to the
rupture of the S–S bonds. In Cu<sub>1.94</sub>S, which lacks
S–S bonds, this mechanism should not be accessible. This hypothesis
was proven by the experimental evidence that adding ascorbic acid
increased the fraction of metal ions incorporated in the covellite
nanocrystals, while it had no noticeable effect on the Cu<sub>1.94</sub>S ones. Once inside the covellite particles, Cd<sup>2+</sup> and
Hg<sup>2+</sup> cations engaged in exchange reactions, pushing the
expelled Cu<sup>+</sup> ions toward the not-yet exchanged regions
in the same particles, or out to the solution, from where they could
be recaptured by other covellite nanoparticles/domains. Because no
good solvating agent for Cu ions was present in solution, they essentially
remained in the nanocrystals
<i>Ab Initio</i> Structure Determination of Cu<sub>2–<i>x</i></sub>Te Plasmonic Nanocrystals by Precession-Assisted Electron Diffraction Tomography and HAADF-STEM Imaging
We
investigated pseudo-cubic Cu<sub>2–<i>x</i></sub>Te nanosheets using electron diffraction tomography and high-resolution
HAADF-STEM imaging. The structure of this metastable nanomaterial,
which has a strong localized surface plasmon resonance in the near-infrared
region, was determined <i>ab initio</i> by 3D electron diffraction
data recorded in low-dose nanobeam precession mode, using a new generation
background-free single-electron detector. The presence of two different,
crystallographically defined modulations creates a 3D connected vacancy
channel system, which may account for the strong plasmonic response
of this material. Moreover, a pervasive rotational twinning is observed
for nanosheets as thin as 40 nm, resulting in a tetragonal pseudo-symmetry
Post-Synthesis Incorporation of 64Cu in CuS Nanocrystals to Radiolabel Photothermal Probes: A Feasible Approach for Clinics
We report a simple method for the incorporation of Cu(I) or 64Cu(I) radionuclides in covellite nanocrystals (CuS NCs). After the in situ reduction of Cu(II) or 64Cu(II) ions by ascorbic acid, their incorporation in PEG-coated CuS NCs takes place at room temperature. In all the reaction steps, the stability of the NCs under physiological conditions was ensured. The copper incorporation reaction could also take place on CuS NCs bearing biotin molecules at their surface, with no detrimental effects on the specific binding affinity of the NCs toward streptavidin after incorporation. At low loading of Cu ions, the strong near-infrared (NIR) absorption band of the starting CuS NCs was essentially preserved, which allowed for efficient plasmonic photothermal therapy. The combined presence in the NCs of 64Cu ions, well suitable for positron emission tomography, and of free carriers responsible for the NIR absorption, should enable their theranostic use as radiotracers and as photothermal probes in tumor ablation treatments. Moreover, the simplicity of the preparation scheme, which involves the use of radioactive species only as a last step, makes the protocol easily transferable to the clinical practice.ISSN:0002-7863ISSN:1520-512