Cu Vacancies Boost Cation Exchange Reactions in Copper Selenide Nanocrystals.
Cu Vacancies Boost Cation Exchange Reactions in Copper Selenide Nanocrystals.
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DOI：
10.1021/jacs.5b03868
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发表时间：
2015-07-29
影响因子：
15
通讯作者：
Manna L
中科院分区：
文献类型：
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作者：
Lesnyak V;Brescia R;Messina GC;Manna L
我们使用两种不同的二价离子作为客体阳离子（Zn2+和Cd2+）研究了硒化铜纳米晶体中的阳离子交换反应，并比较了接近化学计量（即Cu2Se）纳米晶体与非化学计量（Cu2-xSe）纳米晶体的反应性，以深入了解纳米尺度的阳离子交换机制。我们发现，大密度铜空位的存在显着加速了室温下的交换过程，并证实了空位扩散是这些反应的主要驱动因素之一。部分交换的样品表现出由共享外延界面的不混溶域组成的类似两面神(Janus)的异质结构。没有观察到合金或核壳结构。膦（如三正辛基膦）在这些反应中的作用是多方面的：除了在交换过程中充当离开纳米颗粒的 Cu+ 离子的选择性溶剂化配体之外，它们还通过将大量的硒萃取到溶液相中来实现阴离子扩散，这可能会进一步促进交换过程。在较高温度 (150 °C) 下运行的反应中，铜空位很快从纳米晶体中消除，并且初始 Cu2Se 和 Cu2-xSe 样品之间 Cu 化学计量以及反应性的主要差异迅速消除。这些实验表明，在本工作的特定条件下，阳离子交换在室温下比在较高温度下更有效。
We have investigated cation exchange reactions in copper selenide nanocrystals using two different divalent ions as guest cations (Zn2+ and Cd2+) and comparing the reactivity of close to stoichiometric (that is, Cu2Se) nanocrystals with that of nonstoichiometric (Cu2–xSe) nanocrystals, to gain insights into the mechanism of cation exchange at the nanoscale. We have found that the presence of a large density of copper vacancies significantly accelerated the exchange process at room temperature and corroborated vacancy diffusion as one of the main drivers in these reactions. Partially exchanged samples exhibited Janus-like heterostructures made of immiscible domains sharing epitaxial interfaces. No alloy or core–shell structures were observed. The role of phosphines, like tri-n-octylphosphine, in these reactions, is multifaceted: besides acting as selective solvating ligands for Cu+ ions exiting the nanoparticles during exchange, they also enable anion diffusion, by extracting an appreciable amount of selenium to the solution phase, which may further promote the exchange process. In reactions run at a higher temperature (150 °C), copper vacancies were quickly eliminated from the nanocrystals and major differences in Cu stoichiometries, as well as in reactivities, between the initial Cu2Se and Cu2–xSe samples were rapidly smoothed out. These experiments indicate that cation exchange, under the specific conditions of this work, is more efficient at room temperature than at higher temperature.