Physical Chemistry, TU Dresden , Bergstr. 66b, 01062 Dresden, Germany.
IMEM-CNR , Parco Area delle Scienze, 37/A, 43124 Parma, Italy.
J Am Chem Soc. 2017 Jul 19;139(28):9583-9590. doi: 10.1021/jacs.7b03706. Epub 2017 Jul 10.
Stoichiometric CuSe nanocrystals were synthesized in either cubic or hexagonal (metastable) crystal structures and used as the host material in cation exchange reactions with Pb 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 CuSe nanocrystals to Pb cations led to the initial formation of PbSe unselectively on the overall surface of the host nanocrystals, generating CuSe@PbSe core@shell nanoheterostructures. The formation of such intermediates was attributed to the low diffusivity of Pb ions inside the host lattice and to the absence of preferred entry points in cubic CuSe. On the other hand, in hexagonal CuSe nanocrystals, the entrance of Pb ions generated PbSe stripes "sandwiched" in between hexagonal CuSe domains. These peculiar heterostructures formed as a consequence of the preferential diffusion of Pb ions through specific (a, b) planes of the hexagonal CuSe 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.
等摩尔比的 CuSe 纳米晶可合成出立方或六方（亚稳）晶体结构，并可作为与 Pb 离子进行阳离子交换反应的主体材料。即使交换的最终产物在这两种情况下都是岩盐型 PbSe 纳米晶，我们在这里表明，起始纳米晶的晶体结构对交换途径有很强的影响。暴露在 Pb 阳离子中的立方 CuSe 纳米晶导致 PbSe 非选择性地在主体纳米晶的整个表面上形成，生成 CuSe@PbSe 核壳纳米异质结构。形成这种中间体归因于 Pb 离子在主体晶格内的低扩散率以及在立方 CuSe 中不存在优先进入点。另一方面，在六方 CuSe 纳米晶中，Pb 离子的进入会生成夹在六方 CuSe 畴之间的 PbSe 条纹。这些特殊的异质结构是由于 Pb 离子通过六方 CuSe 结构的特定（a，b）面优先扩散而形成的，这些面的特点是几乎空的八面体位置。我们的发现表明，部分阳离子交换反应形成的纳米异质结构的形态不仅与 NC 主体材料有关，而且与其晶体结构密切相关。
