Mechanistic insight into gold nanorod transformation in nanoscale confinement of ZIF-8
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Mechanistic insight into gold nanorod transformation in nanoscale confinement of ZIF-8 Cheongwon Bae1, Jaedeok Lee1, Lehan Yao2, Suhyeon Park1, Yeonju Lee1, Jieun Lee1, Qian Chen2,3,4,5, and Juyeong Kim1 () 1
Department of Chemistry and Research Institute of Natural Sciences, Gyeongsang National University, Jinju 52828, South Korea Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA 3 Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA 4 Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA 5 Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA 2
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 17 May 2020 / Revised: 5 August 2020 / Accepted: 7 August 2020
ABSTRACT Core–shell hybrid nanomaterials have shown new properties and functions that are not attainable by their single counterparts. Nanoscale confinement effect by porous inorganic shells in the hybrid nanostructures plays an important role for chemical transformation of the core nanoparticles. However, metal–organic frameworks (MOFs) have been rarely applied for understanding mechanical insight into such nanoscale phenomena in confinement, although MOFs would provide a variety of properties for the confining environment than other inorganic shells such as silica and zeolite. Here, we examine chemical transformation of a gold nanorod core enclosed by a zeolitic imidazolate framework (ZIF) through chemical etching and regrowth, followed by quantitative analysis in the core dimension and curvature. We find the nanorod core shows template-effective behavior in its morphological transformation. In the etching event, the nanorod core is spherically carved from its tips. The regrowth on the spherically etched core inside the ZIF gives rise to formation of a raspberry-like branched nanostructure in contrast to the growth of an octahedral shape in bulk condition. We attribute the shell-directed regrowth to void space generated at the interfaces between the etched core and the ZIF shell, intercrystalline gaps in multi-domain ZIF shells, and local structural deformation from the acidic reaction conditions.
KEYWORDS nanoscale confinement, core–shell structure, gold nanorod, metal–organic framework, oxidative etching, reductive regrowth
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Introduction
Hybrid nanomaterials, composed of a nanoparticle core and a porous inorganic shell, have shown unique properties and new functions in sensing [1–3], catalysis [4–6], and solid-state reaction [7–9] that cannot be achieved by their single component. The incorporation of the porous shell can allow stability of the nanoparticle core, which is otherwise often sensitive and vulnerable in the solution phase. Depending on the shell porosity and polarity, such hybrid nanomaterials can be utilized as a molecular selective sensor [10, 11]. Catalytic nanoparticle cores
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