A Mechanistic Study on the Nucleation and Growth of Au on Pd Seeds with a Cubic or Octahedral Shape

He, Guannan; Zeng, Jie; Jin, Mingshang; Zhang, Hui; Lü, Ning; Wang, Jinguo; Kim, Moon J.; Xia, Younan

doi:10.1002/cctc.201200205

Cited by 31 publications

(34 citation statements)

References 120 publications

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“…In the following discussion, we refer to them as "Pd cubic seeds" for simplicity. We chose them as seeds for two major reasons: (i) they had a well-defined shape, together with a set of low-index facets on the surface (8,9); and (ii) their side faces are blocked by Br -ions to ensure selective deposition of atoms onto the corner sites during seed-mediated growth (10)(11)(12). These two distinctive features allowed us to easily track the deposition of atoms and their surface diffusion during a growth process by analyzing the shape or morphology of the final product.…”

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On the role of surface diffusion in determining the shape or morphology of noble-metal nanocrystals

Xia

Xie

Liu

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Controlling the shape or morphology of metal nanocrystals is central to the realization of their many applications in catalysis, plasmonics, and electronics. In one of the approaches, the metal nanocrystals are grown from seeds of certain crystallinity through the addition of atomic species. In this case, manipulating the rates at which the atomic species are added onto different crystallographic planes of a seed has been actively explored to control the growth pattern of a seed and thereby the shape or morphology taken by the final product. Upon deposition, however, the adsorbed atoms (adatoms) may not stay at the same sites where the depositions occur. Instead, they can migrate to other sites on the seed owing to the involvement of surface diffusion, and this could lead to unexpected deviations from a desired growth pathway. Herein, we demonstrated that the growth pathway of a seed is indeed determined by the ratio between the rates for atom deposition and surface diffusion. Our result suggests that surface diffusion needs to be taken into account when controlling the shape or morphology of metal nanocrystals. seeded growth | shape control | noble metals S urface diffusion is a general process that involves the motion of adsorbed atoms (adatoms), molecules, or atomic clusters on the surface of a solid material (1, 2). Over the past decades, it has emerged as an important concept in many areas of surface science, including catalysis, epitaxial growth, and electromigration of voids (3-7). Here, we demonstrated that surface diffusion also plays a pivotal role in determining the growth pathway of a seed and thus the shape or morphology taken by the final product in a solutionphase synthesis of metal nanocrystals. Fig. 1 schematically illustrates four possible pathways for the growth of a cubic seed. As a model system, we focused on Pd nanocubes with slight truncation at corners and edges, together with six side faces passivated by chemisorbed Br -ions. In the following discussion, we refer to them as "Pd cubic seeds" for simplicity. We chose them as seeds for two major reasons: (i) they had a well-defined shape, together with a set of low-index facets on the surface (8, 9); and (ii) their side faces are blocked by Br -ions to ensure selective deposition of atoms onto the corner sites during seed-mediated growth (10-12). These two distinctive features allowed us to easily track the deposition of atoms and their surface diffusion during a growth process by analyzing the shape or morphology of the final product.The newly formed Pd atoms resulting from the reduction of a Pd precursor are expected to deposit at the corners of a cubic seed because the side faces are blocked by the chemisorbed Br -ions (Fig. 1A, 1). Upon deposition, there will be two different options for these adatoms: staying at the corner sites or migrating to other sites, including edges and side faces, through surface diffusion (Fig. 1A, 2 and 3). It should be pointed out that only surface diffusion was allowed here to move atoms from corners to edg...

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On the role of surface diffusion in determining the shape or morphology of noble-metal nanocrystals

Xia

Xie

Liu

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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370

457

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“…Most recently, our group demonstrated that kinetic control is a simple and versatile means for achieving siteselective overgrowth. [7,9] By controlling the rate at which Ag atoms are formed in a solution, for example, we could confine the nucleation and growth of Ag to one, three, or six of the {100} side faces of a Pd cubic seed. [9] As a result, Pd-Ag bimetallic nanocrystals with both Pd and Ag being exposed on the surface were obtained in high yields.…”

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“…[5e, 6,7] Owing to the formation of a core-shell structure, only those atoms situated on the outer surface of such a bimetallic nanocrystal are available for catalyzing chemical reactions. In comparison, it will be a significant advantage to formulate a bimetallic nanocrystal into a core-frame structure, in which the atoms of both the core and frame portions will be accessible to reactants.…”

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Synthesis of Pd‐Rh Core–Frame Concave Nanocubes and Their Conversion to Rh Cubic Nanoframes by Selective Etching of the Pd Cores

et al. 2012

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“…A good example is the VIP article by Xia et al, which is featured on the cover of this issue. [7] By a seed-mediated growth mechanism, the authors fabricated bimetallic nanocubes with controlled surface morphologies. By measuring the oxidation of ascorbic acid they concluded that the Pd@Au core-shell nanocubes with concave surfaces exhibited higher activity than nanocubes with flat surfaces.…”

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Editorial: Catalyst Synthesis by Design for the Understanding of Catalysis

Yu¹,

Tao²,

Liu³

2012

ChemCatChem

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Catalysis plays a critical role in our daily life, from energy to healthcare and from clothing to the environment. Heterogeneous catalysis usually occurs on solid surfaces that provide the appropriate electronic and/or geometric environment. The ultimate goal of research on heterogeneous catalysis is to provide a fundamental understanding of the nature of active sites toward the design of efficient heterogeneous catalysts that provide highest activity, 100 % selectivity, and long-term stability. A catalytic reaction, by its nature, involves atomic-scale and nanoscale entities that interact dynamically with reactant molecules. To better understand the complex processes of heterogeneous catalysis requires better control of the structure and chemistry of the active sites. Advancement in synthesis of nanostructured catalysts, such as shape and size control of particles or pores, modification of surface adsorption energies by compositional and structural modulation, fabrication of unique active sites, and manipulation of particle-support interactions, etc., not only provides better-controlled active sites for fundamental studies of heterogeneous catalysis, but also has practical implications for developing improved or novel industrial catalysts for applications in energy, environment, and sustainability.

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A Mechanistic Study on the Nucleation and Growth of Au on Pd Seeds with a Cubic or Octahedral Shape

Cited by 31 publications

References 120 publications

On the role of surface diffusion in determining the shape or morphology of noble-metal nanocrystals

On the role of surface diffusion in determining the shape or morphology of noble-metal nanocrystals

Synthesis of Pd‐Rh Core–Frame Concave Nanocubes and Their Conversion to Rh Cubic Nanoframes by Selective Etching of the Pd Cores

Editorial: Catalyst Synthesis by Design for the Understanding of Catalysis

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