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Selective cation exchange in the core region of Cu2-xSe/Cu2-xS core/shell nanocrystals.

Miszta K, Gariano G, Brescia R, Marras S, De Donato F, Ghosh S, De Trizio L, Manna L - J. Am. Chem. Soc. (2015)

Bottom Line: We studied cation exchange (CE) in core/shell Cu2-xSe/Cu2-xS nanorods with two cations, Ag(+) and Hg(2+), which are known to induce rapid exchange within metal chalcogenide nanocrystals (NCs) at room temperature.These experiments prove that CE in copper chalcogenide NCs is facilitated by the high diffusivity of guest cations in the lattice, such that they can probe the whole host structure and identify the preferred regions where to initiate the exchange.For both guest ions, CE is thermodynamically driven as it aims for the formation of the chalcogen phase characterized by the lower solubility under the specific reaction conditions.

View Article: PubMed Central - PubMed

Affiliation: Department of Nanochemistry, Istituto Italiano di Tecnologia (IIT) , via Morego, 30, 16163 Genova, Italy.

ABSTRACT
We studied cation exchange (CE) in core/shell Cu2-xSe/Cu2-xS nanorods with two cations, Ag(+) and Hg(2+), which are known to induce rapid exchange within metal chalcogenide nanocrystals (NCs) at room temperature. At the initial stage of the reaction, the guest ions diffused through the Cu2-xS shell and reached the Cu2-xSe core, replacing first Cu(+) ions within the latter region. These experiments prove that CE in copper chalcogenide NCs is facilitated by the high diffusivity of guest cations in the lattice, such that they can probe the whole host structure and identify the preferred regions where to initiate the exchange. For both guest ions, CE is thermodynamically driven as it aims for the formation of the chalcogen phase characterized by the lower solubility under the specific reaction conditions.

No MeSH data available.


Related in: MedlinePlus

XRD patternsof (c) pristine, (b) Ag+, and (a) Hg2+ partiallyexchanged Cu2–xSe/Cu2–xS NRs, with bulk reflectionsof hexagonal Cu2S (high chalcocite, ICDD 98-016-6578) andorthorhombic Ag2Se (naumannite, ICDD 98-026-1822). Reflectionsof the Cu2Se “chalcocite-like” phase areadapted from ref (7a). The Bragg peaks emerging after Hg2+ partial exchangecorrespond to the bulk reflections of hexagonal CdSe (cadmoselite,ICDD 96-901-6057). In all samples, other minor peaks (labeled with*) can be assigned to a substoichiometric tetragonal Cu116S64 phase (roxbyite, ICDD 96-901-5183), probably appearingdue to slight oxidation of the NC films exposed to air during patternacquisition.
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fig3: XRD patternsof (c) pristine, (b) Ag+, and (a) Hg2+ partiallyexchanged Cu2–xSe/Cu2–xS NRs, with bulk reflectionsof hexagonal Cu2S (high chalcocite, ICDD 98-016-6578) andorthorhombic Ag2Se (naumannite, ICDD 98-026-1822). Reflectionsof the Cu2Se “chalcocite-like” phase areadapted from ref (7a). The Bragg peaks emerging after Hg2+ partial exchangecorrespond to the bulk reflections of hexagonal CdSe (cadmoselite,ICDD 96-901-6057). In all samples, other minor peaks (labeled with*) can be assigned to a substoichiometric tetragonal Cu116S64 phase (roxbyite, ICDD 96-901-5183), probably appearingdue to slight oxidation of the NC films exposed to air during patternacquisition.

Mentions: These findings were supported by elemental analyses (viaSTEM-EDS),which yielded a Hg/Se ratio of ∼1 and a Ag/Se ratio of ∼2for the Hg-treated and Ag-treated NRs, respectively (Table S1). High-resolution TEM (HRTEM) images of partiallyexchanged Cu2–xSe/Cu2–xS NRs, with both Ag+ and Hg2+ ions, reported in Figure S5, confirmedthe selective ion replacement in the core region and, importantly,showed a continuous shell, exhibiting no cracks, surrounding the cores.The exposure of Cu2–xSe/Cu2–xS NRs to a higher amount of Ag+ or Hg2+ ions led to an almost complete replacementof Cu+ ions (see Figures S6, S7 and Table S1). The peculiarity of these results stands in the evidencethat cation replacement in the Cu2–xSe core must be preceded, both for Ag+ and Hg2+ cations, by diffusion of cations through the Cu2–xS shell. The structural transformations of the core/shellCu2–xSe/Cu2–xS NRs upon partial CE were monitored via X-ray diffraction(XRD). The XRD patterns of the pristine Cu2–xSe/Cu2–xS NRs (Figure 3c) were dominatedby the hexagonal Cu2S (high chalcocite) peaks, with otherminor reflections ascribable to the metastable Cu2Se “chalcocite-like”phase, as previously reported by us.7a TheXRD patterns of partially exchanged NRs, instead, evidenced in bothcases the presence of high chalcocite Cu2S, together witha second majority phase that, in the case of Ag+-treatedNRs, could be indexed according to the orthorhombic Ag2Se (naummanite) phase (see Figure 3b), while for the Hg2+-treated rods, itcould not be indexed to any known bulk HgSe or to any alloyed HgSexS1–x phase.


Selective cation exchange in the core region of Cu2-xSe/Cu2-xS core/shell nanocrystals.

Miszta K, Gariano G, Brescia R, Marras S, De Donato F, Ghosh S, De Trizio L, Manna L - J. Am. Chem. Soc. (2015)

XRD patternsof (c) pristine, (b) Ag+, and (a) Hg2+ partiallyexchanged Cu2–xSe/Cu2–xS NRs, with bulk reflectionsof hexagonal Cu2S (high chalcocite, ICDD 98-016-6578) andorthorhombic Ag2Se (naumannite, ICDD 98-026-1822). Reflectionsof the Cu2Se “chalcocite-like” phase areadapted from ref (7a). The Bragg peaks emerging after Hg2+ partial exchangecorrespond to the bulk reflections of hexagonal CdSe (cadmoselite,ICDD 96-901-6057). In all samples, other minor peaks (labeled with*) can be assigned to a substoichiometric tetragonal Cu116S64 phase (roxbyite, ICDD 96-901-5183), probably appearingdue to slight oxidation of the NC films exposed to air during patternacquisition.
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4591528&req=5

fig3: XRD patternsof (c) pristine, (b) Ag+, and (a) Hg2+ partiallyexchanged Cu2–xSe/Cu2–xS NRs, with bulk reflectionsof hexagonal Cu2S (high chalcocite, ICDD 98-016-6578) andorthorhombic Ag2Se (naumannite, ICDD 98-026-1822). Reflectionsof the Cu2Se “chalcocite-like” phase areadapted from ref (7a). The Bragg peaks emerging after Hg2+ partial exchangecorrespond to the bulk reflections of hexagonal CdSe (cadmoselite,ICDD 96-901-6057). In all samples, other minor peaks (labeled with*) can be assigned to a substoichiometric tetragonal Cu116S64 phase (roxbyite, ICDD 96-901-5183), probably appearingdue to slight oxidation of the NC films exposed to air during patternacquisition.
Mentions: These findings were supported by elemental analyses (viaSTEM-EDS),which yielded a Hg/Se ratio of ∼1 and a Ag/Se ratio of ∼2for the Hg-treated and Ag-treated NRs, respectively (Table S1). High-resolution TEM (HRTEM) images of partiallyexchanged Cu2–xSe/Cu2–xS NRs, with both Ag+ and Hg2+ ions, reported in Figure S5, confirmedthe selective ion replacement in the core region and, importantly,showed a continuous shell, exhibiting no cracks, surrounding the cores.The exposure of Cu2–xSe/Cu2–xS NRs to a higher amount of Ag+ or Hg2+ ions led to an almost complete replacementof Cu+ ions (see Figures S6, S7 and Table S1). The peculiarity of these results stands in the evidencethat cation replacement in the Cu2–xSe core must be preceded, both for Ag+ and Hg2+ cations, by diffusion of cations through the Cu2–xS shell. The structural transformations of the core/shellCu2–xSe/Cu2–xS NRs upon partial CE were monitored via X-ray diffraction(XRD). The XRD patterns of the pristine Cu2–xSe/Cu2–xS NRs (Figure 3c) were dominatedby the hexagonal Cu2S (high chalcocite) peaks, with otherminor reflections ascribable to the metastable Cu2Se “chalcocite-like”phase, as previously reported by us.7a TheXRD patterns of partially exchanged NRs, instead, evidenced in bothcases the presence of high chalcocite Cu2S, together witha second majority phase that, in the case of Ag+-treatedNRs, could be indexed according to the orthorhombic Ag2Se (naummanite) phase (see Figure 3b), while for the Hg2+-treated rods, itcould not be indexed to any known bulk HgSe or to any alloyed HgSexS1–x phase.

Bottom Line: We studied cation exchange (CE) in core/shell Cu2-xSe/Cu2-xS nanorods with two cations, Ag(+) and Hg(2+), which are known to induce rapid exchange within metal chalcogenide nanocrystals (NCs) at room temperature.These experiments prove that CE in copper chalcogenide NCs is facilitated by the high diffusivity of guest cations in the lattice, such that they can probe the whole host structure and identify the preferred regions where to initiate the exchange.For both guest ions, CE is thermodynamically driven as it aims for the formation of the chalcogen phase characterized by the lower solubility under the specific reaction conditions.

View Article: PubMed Central - PubMed

Affiliation: Department of Nanochemistry, Istituto Italiano di Tecnologia (IIT) , via Morego, 30, 16163 Genova, Italy.

ABSTRACT
We studied cation exchange (CE) in core/shell Cu2-xSe/Cu2-xS nanorods with two cations, Ag(+) and Hg(2+), which are known to induce rapid exchange within metal chalcogenide nanocrystals (NCs) at room temperature. At the initial stage of the reaction, the guest ions diffused through the Cu2-xS shell and reached the Cu2-xSe core, replacing first Cu(+) ions within the latter region. These experiments prove that CE in copper chalcogenide NCs is facilitated by the high diffusivity of guest cations in the lattice, such that they can probe the whole host structure and identify the preferred regions where to initiate the exchange. For both guest ions, CE is thermodynamically driven as it aims for the formation of the chalcogen phase characterized by the lower solubility under the specific reaction conditions.

No MeSH data available.


Related in: MedlinePlus