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Role of the Crystal Structure in Cation Exchange Reactions Involving Colloidal Cu₂Se Nanocrystals.

ABSTRACT: Stoichiometric Cu₂Se nanocrystals were synthesized in either cubic or hexagonal (metastable) crystal structures and used as the host material in cation exchange reactions with Pb²⁺ ions. Even if the final product of the exchange, in both cases, was rock-salt PbSe nanocrystals, we show here that the crystal structure of the starting nanocrystals has a strong influence on the exchange pathway. The exposure of cubic Cu₂Se nanocrystals to Pb²⁺ cations led to the initial formation of PbSe unselectively on the overall surface of the host nanocrystals, generating Cu₂Se@PbSe core@shell nanoheterostructures. The formation of such intermediates was attributed to the low diffusivity of Pb²⁺ ions inside the host lattice and to the absence of preferred entry points in cubic Cu₂Se. On the other hand, in hexagonal Cu₂Se nanocrystals, the entrance of Pb²⁺ ions generated PbSe stripes "sandwiched" in between hexagonal Cu₂Se domains. These peculiar heterostructures formed as a consequence of the preferential diffusion of Pb²⁺ ions through specific (a, b) planes of the hexagonal Cu₂Se structure, which are characterized by almost empty octahedral sites. Our findings suggest that the morphology of the nanoheterostructures, formed upon partial cation exchange reactions, is intimately connected not only to the NC host material, but also to its crystal structure.

SUBMITTER: Gariano G

PROVIDER: S-EPMC6105078 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature

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Role of the Crystal Structure in Cation Exchange Reactions Involving Colloidal Cu2Se Nanocrystals.

Gariano Graziella G Lesnyak Vladimir V Brescia Rosaria R Bertoni Giovanni G Dang Zhiya Z Gaspari Roberto R De Trizio Luca L Manna Liberato L

Journal of the American Chemical Society 20170710 28

Stoichiometric Cu2Se nanocrystals were synthesized in either cubic or hexagonal (metastable) crystal structures and used as the host material in cation exchange reactions with Pb2+ ions. Even if the final product of the exchange, in both cases, was rock-salt PbSe nanocrystals, we show here that the crystal structure of the starting nanocrystals has a strong influence on the exchange pathway. The exposure of cubic Cu2Se nanocrystals to Pb2+ cations led ...[more]

PMID: 28644018

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Project description:Augmenting the oriented attachment (OA) crystal growth phenomena, herein, we demonstrate fabrication of ultrathin CuO nanowires from self-assembled one-dimensional (1D) nanowires of Cu(OH)2 nanocrystals. A facile environmentally benign sol-gel approach, which utilizes base-catalyzed hydrolysis followed by directed self-assembly and crystal growth of nanocrystals, is developed to prepare Cu(OH)2 nanowires. The sol of Cu(OH)2 nanocrystals shows aggregative self-assembly guided by the OA crystal growth process to form ultrathin Cu(OH)2 nanowires, with an average length of 675 ± 4 nm and diameter of 6 ± 2 nm. The time-dependent UV-visible spectral traces, along with real-time imaging of nanocrystals self-assembly and growth under the transmission electron microscope, are evidenced the concept of the OA crystal growth directed self-assembly, yielding 1D colloidal nanoarrays of Cu(OH)2. The powder XRD traces collected during the self-assembly and crystal growth process reveal the directional aggregative crystal growth along the facet of [001], confirming the OA directed crystal growth and fusion of nanocrystals to yield 1D nanostructures. The gradual blue-shift in optical absorption maxima from 770 nm in initial precursor solution, to 670 nm for Cu(OH)2 nanocrystals sol, and finally to 647 nm for self-assembled 1D Cu(OH)2 nanowires have further evidenced the formation of Cu(OH)2 nanowires. Upon subjecting self-assembled Cu(OH)2 nanowires for post-annealing treatment, ultrathin CuO nanowires with average length of 7 ± 0.50 μm and diameter of 27 ± 2 nm is obtained in high purity. The experimental powder XRD patterns of Cu(OH)2 and CuO nanowires match the simulated XRD patterns, indexing the crystal unit cell structures to orthorhombic and monoclinic, respectively. The tailored narrow optical band gaps for Cu(OH)2 and CuO nanowires are found to be 1.51 eV and 1.10 eV. The theoretical band gap predicted for Cu(OH)2 nanowires is 1.52 eV and is in good agreement with its optical band gap, whereas theoretical band computed for CuO nanowires is 0.13 eV lower than from its optical band gap.

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Role of the Crystal Structure in Cation Exchange Reactions Involving Colloidal Cu₂Se Nanocrystals.

Publications

Role of the Crystal Structure in Cation Exchange Reactions Involving Colloidal Cu<sub>2</sub>Se Nanocrystals.

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