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.

One‐Dimensional Cuprous Selenide Nanostructures with Switchable Plasmonic and Super‐ionic Phase Attributes

“…Zuschriften hcp Se 2À arrangement of these wurtzite CdSe domains is preserved in the cation exchange reaction [11,14] resulting in the attainment of hcp domains in the otherwise pseudo-cubic Cu 2 Se NWs.T he 1 % 7nmC u 2 Se NWs do not show diffraction peaks corresponding to the hcp phase,e xcept for aw eak shoulder peak at 2q % 28.58 8.T his difference between the Cu 2 Se NWs of the two 1 is due to the fact that the zinc blende phase of CdSe becomes energetically more favorable at smaller sizes. [15] From HRTEM and XRD analyses,t he Cu 2 Se NWs are found to be in the vacancy-ordered b-phase.W esubjected the NWs to differential scanning calorimetry (DSC) to determine the temperature at which the NWs could be transitioned into the SI a-phase (Figure 4a,b).…”

“…The cubic zinc blende and hexagonal wurtzite polymorphs of CdSe have a low energy difference, which commonly results in a polytypism where CdSe NWs can have both zinc blende and wurtzite domains separated by stacking faults along their growth direction. The hcp Se 2− arrangement of these wurtzite CdSe domains is preserved in the cation exchange reaction resulting in the attainment of hcp domains in the otherwise pseudo‐cubic Cu 2 Se NWs. The Ø≈7 nm Cu 2 Se NWs do not show diffraction peaks corresponding to the hcp phase, except for a weak shoulder peak at 2 θ ≈28.5°.…”

Structural and compositional control in copper selenide nanocrystals for light-induced self-repairable electrodes

“…Not only composition, but the arrangement of atoms in a given structural phase is also a crucial parameter to control electronic, thermal, and chemical properties of copper selenide [20] , [21] , [22] , [23] . For example, Pb +2 ions selectively react with different planes of cubic and hexagonal stoichiometric Cu 2 Se NCs in cation exchange reactions [24] . Owing to these magnificent characteristics, compositional and structural control in copper selenide NCs is highly desirable for their specific scientific and technological applications, which poses a general challenge for researchers to discover new synthesis methodologies.…”

“…Typical methodology discovery is conducted with conventional solution chemistry, where either the concentration of chemical precursors is varied [25] , or post-processing techniques, such as cation exchange or thermal annealing, are used to control chemical composition or crystallinity/phase of materials [24] , [26] , [27] . In the former case, the amount of required precursor needs to be calculated and measured precisely for a given chemical composition.…”

Smart Assembly of Sulfide Heterojunction Photocatalysts with Well‐Defined Interfaces for Direct Z‐Scheme Water Splitting under Visible Light

“…Following this mechanism, some half‐reaction photocatalysts, such as WO 3 , BiVO 4 , Fe 2 O 3 , CuInS 2 , and CoS 2 , have been merged into CdS to assemble direct Z‐scheme hybrid photocatalysts by various methods in recent years. To establish Z‐scheme heterojunctions, cation exchange has attracted considerable attention because it provides a predictable means to design high‐quality interfacial contacts with atomic precision . γ‐MnS, a typical visible‐light‐responsive semiconductor (band gap≈2.1 eV), processes a suitable band potential for O 2 evolution from water and could be a candidate for a Z‐scheme hybrid photocatalyst.…”