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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.


CE in “inverted”core/shell Cu2–xS/Cu2–xSe NRs,with Ag+ and Hg2+ ions. HAADF-STEM images ofrepresentative “inverted” NRs partially exchanged with(a) Ag+ or (b) Hg2+, along with the correspondingSTEM-EDS elemental maps. The scale bars in the images are 20 nm.
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fig4: CE in “inverted”core/shell Cu2–xS/Cu2–xSe NRs,with Ag+ and Hg2+ ions. HAADF-STEM images ofrepresentative “inverted” NRs partially exchanged with(a) Ag+ or (b) Hg2+, along with the correspondingSTEM-EDS elemental maps. The scale bars in the images are 20 nm.

Mentions: These experiments were then benchmarked against CE on CdSe/CdSnanoheterostructures. In cadmium chalcogenide structures, where thedensity of vacancies is considerably lower than in Cu-based ones,ion diffusion proceeds mostly interstially. When CdSe/CdS NRs werepartially exchanged with Ag+ ions, no preferential exchangeof the core was observed (see Figure S9). Instead, at the early stage of the CE process, Ag-containing domainsstarted “decorating” the CdS outer layer, accompaniedby the replacement of Cd2+ ions at the tips of the rods,producing heterostructures similar to the Ag2S-CdS NRsreported in the literature.2a Also, ina previous work of ours, we studied CE involving CdSe/CdS octapod-shapedNCs with Cu+ ions, in conditions that are similar to thoseof this work;2c in that case too, the CEstarted at the extremities of the CdS pods and left the CdSe coreunaltered. Furthermore, our data are in line with those of recentworks where it was shown that partial exchange of core/shell CdSe/CdSnanoplatelets and NRs with Cu+ ions resulted in a selectivereplacement of Cd2+ cations in the CdS shell.13 In the light of the data discussed on Cu2–xSe/Cu2–xS NRs so far, these results suggest that, in CdSe/CdS NRs,even if the thermodynamically preferred phases would be Cu2Se and Ag2Se (Table 1), the limited diffusivities of both the entering Cu+ or Ag+ cations and the exiting Cd2+ ions are mainly responsible for the preferential nucleation of theCu2S or Ag2S phases at regions of the NCs closeto their surface. We also ran control experiments starting from “inverted”core/shell Cu2–xS/Cu2–xSe NRs, prepared by complete Cu+ exchangeon CdS/CdSe NRs (see SI).8c When partial exchange with Ag+ or Hg2+ ions was carried out on them, the replacement affected selectivelythe shell region (i.e., the Cu2–xSe phase), as shown in Figure 4 (see also Table S1). It is interestingto notice that, in CE reactions involving Hg2+ ions, therewas a substantial anion interdiffusion throughout the NRs (Figure 4b). This furtherproves that CE, affecting in this case mainly the shell region, representsonly the final step of a series of events in which Hg2+ ions had previously probed extended regions inside the rods, inthis case partially “dragging”, along their way, S2– and Se2– ions.


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)

CE in “inverted”core/shell Cu2–xS/Cu2–xSe NRs,with Ag+ and Hg2+ ions. HAADF-STEM images ofrepresentative “inverted” NRs partially exchanged with(a) Ag+ or (b) Hg2+, along with the correspondingSTEM-EDS elemental maps. The scale bars in the images are 20 nm.
© Copyright Policy
Related In: Results  -  Collection

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

fig4: CE in “inverted”core/shell Cu2–xS/Cu2–xSe NRs,with Ag+ and Hg2+ ions. HAADF-STEM images ofrepresentative “inverted” NRs partially exchanged with(a) Ag+ or (b) Hg2+, along with the correspondingSTEM-EDS elemental maps. The scale bars in the images are 20 nm.
Mentions: These experiments were then benchmarked against CE on CdSe/CdSnanoheterostructures. In cadmium chalcogenide structures, where thedensity of vacancies is considerably lower than in Cu-based ones,ion diffusion proceeds mostly interstially. When CdSe/CdS NRs werepartially exchanged with Ag+ ions, no preferential exchangeof the core was observed (see Figure S9). Instead, at the early stage of the CE process, Ag-containing domainsstarted “decorating” the CdS outer layer, accompaniedby the replacement of Cd2+ ions at the tips of the rods,producing heterostructures similar to the Ag2S-CdS NRsreported in the literature.2a Also, ina previous work of ours, we studied CE involving CdSe/CdS octapod-shapedNCs with Cu+ ions, in conditions that are similar to thoseof this work;2c in that case too, the CEstarted at the extremities of the CdS pods and left the CdSe coreunaltered. Furthermore, our data are in line with those of recentworks where it was shown that partial exchange of core/shell CdSe/CdSnanoplatelets and NRs with Cu+ ions resulted in a selectivereplacement of Cd2+ cations in the CdS shell.13 In the light of the data discussed on Cu2–xSe/Cu2–xS NRs so far, these results suggest that, in CdSe/CdS NRs,even if the thermodynamically preferred phases would be Cu2Se and Ag2Se (Table 1), the limited diffusivities of both the entering Cu+ or Ag+ cations and the exiting Cd2+ ions are mainly responsible for the preferential nucleation of theCu2S or Ag2S phases at regions of the NCs closeto their surface. We also ran control experiments starting from “inverted”core/shell Cu2–xS/Cu2–xSe NRs, prepared by complete Cu+ exchangeon CdS/CdSe NRs (see SI).8c When partial exchange with Ag+ or Hg2+ ions was carried out on them, the replacement affected selectivelythe shell region (i.e., the Cu2–xSe phase), as shown in Figure 4 (see also Table S1). It is interestingto notice that, in CE reactions involving Hg2+ ions, therewas a substantial anion interdiffusion throughout the NRs (Figure 4b). This furtherproves that CE, affecting in this case mainly the shell region, representsonly the final step of a series of events in which Hg2+ ions had previously probed extended regions inside the rods, inthis case partially “dragging”, along their way, S2– and Se2– ions.

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.