Hyunjoon Song

Ni@SiO2 yolk-shell nanoreactor catalysts: High temperature stability and recyclability

Nickel-based catalysts have been good candidates for steam reforming of methane, but their stability has been restricted due to the agglomeration among particles at high temperature. In the present work, a new type of Ni@SiO2 yolk-shell nanoreactor framework comprising Ni cores inside hollow silica shells has been prepared through direct silica coating and subsequent selective etching of the metal cores. This nanoreactor framework is remarkably stable at high temperatures up to 973 K, because the silica hollow shells around the nickel cores essentially block particle sintering. The Ni@SiO2 nanoreactor structure is employed as a model catalyst for the steam methane reforming reaction. The catalysts exhibit a continuous conversion rate of methane and hydrogen, and significantly enhanced stability at high temperatures, leading to high recyclability without loss of catalytic activity. These reaction properties are superior to Ni/MCF catalysts, and comparable with state-of-the-art commercial catalysts. This catalyst design can be generalized for other bifunctional systems, such as Co@SiO2 and Fe@SiO2.

A Selective Fluoroionophore Based on BODIPY‐functionalized Magnetic Silica Nanoparticles: Removal of Pb2+ from Human Blood

Get the lead out: The title fluorescence receptor exhibits a high affinity and selectivity for Pb(2+) over competing metal ions in water (see picture) with an overall emission change of approximately 8-fold at the emission maximum for Pb(2+). The fluorescence receptor can remove 96 % of 100 ppb Pb(2+) from human blood, and can be useful and effective for the selective and rapid removal of Pb(2+) in vivo.

Ag-Au-Ag heterometallic nanorods formed through directed anisotropic growth.

The Ag−Au−Ag heterometallic nanorods were synthesized epitaxially though directed anisotropic overgrowth from multiply twinned gold decahedrons and rods. The silver segments were stoichiometrically converted to Ag2S by reaction with sulfide ions, generating Ag2S−Au−Ag2S heterojunction nanorods.

Au@Ag Core–Shell Nanocubes for Efficient Plasmonic Light Scattering Effect in Low Bandgap Organic Solar Cells

In this report, we propose a metal-metal core-shell nanocube (NC) as an advanced plasmonic material for highly efficient organic solar cells (OSCs). We covered an Au core with a thin Ag shell as a scattering enhancer to build Au@Ag NCs, which showed stronger scattering efficiency than Au nanoparticles (AuNPs) throughout the visible range. Highly efficient plasmonic organic solar cells were fabricated by embedding Au@Ag NCs into an anodic buffer layer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and the power conversion efficiency was enhanced to 6.3% from 5.3% in poly[N-9-hepta-decanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] (PCDTBT):[6,6]-phenyl C71-butyric acid methyl ester (PC70BM) based OSCs and 9.2% from 7.9% in polythieno[3,4-b]thiophene/benzodithiophene (PTB7):PC70BM based OSCs. The Au@Ag NC plasmonic PCDTBT:PC70BM-based organic solar cells showed 2.2-fold higher external quantum efficiency enhancement compared to AuNPs devices at a wavelength of 450-700 nm due to the amplified plasmonic scattering effect. Finally, we proved the strongly enhanced plasmonic scattering efficiency of Au@Ag NCs embedded in organic solar cells via theoretical calculations and detailed optical measurements.

Single‐Crystalline Hollow Face‐Centered‐Cubic Cobalt Nanoparticles from Solid Face‐Centered‐Cubic Cobalt Oxide Nanoparticles

Hollow nanoparticles are of great interest because of their applications in catalysis, nanoelectronics, photonics, drug delivery system, nanoreactors, lubrication, and chemical storage. Various known hollow spheres include those composed of carbon, polymers, metals, and inorganic materials. Diverse synthetic methods have been developed to prepare these hollow nanoparticles, such as removal of the templating core, galvanic replacement, and through the Kirkendall effect. Cobalt exhibits hexagonal closed-packed (hcp Co) and face-centered cubic (fcc Co) structures in the bulk, and a metastable cubic structure labeled e-Co in the nanometer range. Cobalt nanostructures have been widely studied because of their potential applications, mainly in ultrahighdensity magnetic storage. However, reports on hollow cobalt nanoparticles are very limited thus far, although they are interesting materials in terms of their unusual magnetic domains and quantum properties. We herein report that fcc Co hollow nanoparallelepipeds have been prepared by thermolysis of fcc CoO solid nanoparallelepipeds in oleylamine (C18H35NH2). The fcc CoO solid nanoparallelepipeds, surprisingly, are reduced by the oleylamine surfactant to form fcc Co hollow nanoparallelepipeds. This new phenomenon could signify an important methodology to produce constituent metal (M) hollow nanoparticles from metal oxide (MO) solid nanoparticles. In our previous work, we reported phaseand sizecontrolled syntheses of hexagonal and cubic CoO nanocrystals (hcp CoO and fcc CoO). The fcc CoO solid nanoparallelepipeds in oleylamine undergoes reduction at high temperatures (270–290 8C) to transform into hollow nanoparallelepipeds composed of cubic metallic Co (fcc Co). Figure 1 shows the evolution of the morphology of fcc Co

Asymmetric Hollow Nanorod Formation through a Partial Galvanic Replacement Reaction

An asymmetric single hollow structure was generated from Ag-Au-Ag heterometal nanorods by a partial galvanic replacement reaction for the first time. The C(2)-symmetry breaking took place because of the random generation of a single pit on only one end of the silver domain at an early stage of the reaction. Careful control of the reaction kinetics could also yield a double-hollow structure on both ends of the silver domain. The resulting single- and double-hollow nanorods exhibited characteristic extinctions in the near-IR range.

Porosity Control of Pd@SiO2 Yolk–Shell Nanocatalysts by the Formation of Nickel Phyllosilicate and Its Influence on Suzuki Coupling Reactions

The surface of Pd@SiO(2) core-shell nanoparticles (1) was simply modified by the formation of nickel phyllosilicate. The addition of nickel salts formed branched nickel phyllosilicates and generated pores in the silica shells, yielding Pd@SiO(2)-Niphy nanoparticles (Niphy = nickel phyllosilicate; 2, 3). By removal of the silica residue, Pd@Niphy yolk-shell nanoparticles (4) was uniformly obtained. The four distinct nanostructures (1-4) were employed as catalysts for Suzuki coupling reactions with aryl bromide and phenylboronic acid, and the conversion yields were in the order of 1 < 2 < 3 < 4 as the pore volume and surface area of the catalysts increased. The reaction rates were strongly correlated with shell porosity and surface exposure of the metal cores. The chemical inertness of nickel phyllosilicate under the basic conditions rendered the catalysts reusable for more than five times without loss of activity.

Plasmonic monitoring of catalytic hydrogen generation by a single nanoparticle probe.

Plasmonic nanostructures such as gold nanoparticles are very useful for monitoring chemical reactions because their optical properties are highly dependent upon the environment surrounding the particle surface. Here, we designed the catalytic structure composed of platinized cadmium sulfide with gold domains as a sensitive probe, and we monitored the photocatalytic decomposition of lactic acid to generate hydrogen gas in situ by single-particle dark-field spectroscopy. The plasmon band shift of the gold probe throughout the reaction exhibits significant particle-to-particle variation, and by simulating the reaction kinetics, the rate constant and structural information (including the diffusion coefficient through the shell and the relative arrangement of the active sites) can be estimated for individual catalyst particles. This approach is versatile for the monitoring of various heterogeneous reactions with distinct components at a single-particle level.

Metal Hybrid Nanoparticles for Catalytic Organic and Photochemical Transformations

In order to understand heterogeneous catalytic reactions, model catalysts such as a single crystalline surface have been widely studied for many decades. However, catalytic systems that actually advance the reactions are three-dimensional and commonly have multiple components including active metal nanoparticles and metal oxide supports. On the other hand, as nanochemistry has rapidly been developed and been applied to various fields, many researchers have begun to discuss the impact of nanochemistry on heterogeneous catalysis. Metal hybrid nanoparticles bearing multiple components are structurally very close to the actual catalysts, and their uniform and controllable morphology is suitable for investigating the relationship between the structure and the catalytic properties in detail. In this Account, we introduce four typical structures of metal hybrid nanoparticles that can be used to conduct catalytic organic and photochemical reactions. Metal@silica (or metal oxide) yolk-shell nanoparticles, in which metal cores exist in internal voids surrounded by thin silica (or metal oxide) shells, exhibited extremely high thermal and chemical stability due to the geometrical protection of the silica layers against the metal cores. The morphology of the metal cores and the pore density of the hollow shells were precisely adjusted to optimize the reaction activity and diffusion rates of the reactants. Metal@metal oxide core-shell nanoparticles and inverted structures, where the cores supported the shells serving an active surface, exhibited high activity with no diffusion barriers for the reactants and products. These nanostructures were used as effective catalysts for various organic and gas-phase reactions, including hydrogen transfer, Suzuki coupling, and steam methane reforming. In contrast to the yolk- and core-shell structures, an asymmetric arrangement of distinct domains generated acentric dumbbells and tipped rods. A large domain of each component added multiple functions, such as magnetism and light absorption, to the catalytic properties. In particular, metal-semiconductor hybrid nanostructures could behave as effective visible photocatalysts for hydrogen evolution and CO oxidation reactions. Resulting from the large surface area and high local concentration of the reactants, a double-shell hollow structure showed reaction activities higher than those of filled nanoparticles. The introduction of plasmonic Au probes into the Pt-CdS double-shell hollow particles facilitated the monitoring of photocatalytic hydrogen generation that occurred on an individual particle surface by single particle measurements. Further development of catalysis research using well-defined metal hybrid nanocatalysts with various in situ spectroscopic tools provides a means of maximizing catalytic performances until they are comparable to or better than those of homogeneous catalysts, and this would have possibly useful implications for industrial applications.

Full-Color Tuning of Surface Plasmon Resonance by Compositional Variation of Au@Ag Core–Shell Nanocubes with Sulfides

In the present study, we demonstrate the precise tuning of surface plasmon resonance over the full visible range by compositional variation of the nanoparticles. The addition of sulfide ions into the Au@Ag core-shell nanocubes generates stable Au@Ag/Ag(2)S core-shell nanoparticles at room temperature, and the plasmon extinction maximum shifts to the longer wavelength covering the entire visible range of 500-750 nm. Based on the optical property, the Au@Ag core-shell nanocubes are employed as a colorimetric sensing framework for sulfide detection in water. The detection limit is measured to be 10 ppb by UV-vis spectroscopy and 200 ppb by naked eyes. Such nanoparticles would be useful for decoration and sensing purposes, due to their precise color tunability and high stability.