12,407 research outputs found
Metal Hybrid Nanoparticles for Catalytic Organic and Photochemical Transformations
No full textIn 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. (Chemical Equation Presented). © 2015 American Chemical Society136361sciescopu
Hybrid gold architectures for sensing and catalytic applications
No full textThis work was supported by the Nano R&D program (2007-02668) and a grant from the
Korea Science and Engineering Foundation (KOSEF), funded by the Korean Government
(MEST) (R11-2007-050-04002-0)
Nanoscale reaction monitoring using localized surface plasmon resonance scatterometry
No full text Heterogeneous reactions are highly dependent upon the local structure and environment of the catalyst surface within a nanoscale. Among numerous techniques for monitoring heterogeneous reactions, dark-field microscopy offers reliable data regardless of specific reaction conditions. In addition, plasmonic nanoprobes provide high sensitivity in a sub-wavelength resolution due to localized surface plasmon resonances susceptible to the dielectric change of objects and surroundings. By clever reaction cell design and data analysis, nanoparticle signals can be parallelly analyzed under variable reaction conditions in a controlled manner. This technique effectively measures the heterogeneity of individual nanoparticles for reaction monitoring. A wide range of chemical and electrochemical reactions have been monitored in situ and in operando at a single-particle level in this way. The advancement of localized surface plasmon scatterometry with simulation techniques approaches sub-particle accuracy in a high temporal resolution up to microseconds. Combining other in situ spectroscopic methods would make dark-field scatterometry a versatile tool for various reaction monitoring and sensing applications. </jats:p
Asymmetric Hollow Nanorod Formation through a Partial Galvanic Replacement Reaction
No full textAn 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.This work was supported by the Pioneer
Research Program under Contract 2008-05103 and by the National Research Foundation, funded by the Korean Government (MEST)
(R11-2007-050-04002-0)
Precise adjutment of structural anisotropy and crystallinity on metal-Fe3O4 hybrid nanoparticles and its influence on magnetic and catalytic properties
No full textIn the present study, we demonstrate the precise adjustment of the morphology and crystallinity of metal (Pd or Au)–Fe3O4 hybrid nanoparticles by reaction kinetics control. The nucleation and growth of the Fe component on the Pd surface are precisely controlled by using a mixture of capping agents, oleylamine and oleic acid. After the oxidation, the resulting Pd–Fe3O4 structures are produced as yolk–shell, irregular core–shell, and dumbbell-like NPs. Along with the morphology change, the average crystal domain size of Fe3O4 and the void gap between the metal cores and the shells are simultaneously adjusted. The crystal domain sizes of Fe3O4 directly influence the magnetic properties, and the structural arrangement of the Pd cores and the Fe3O4 shells leads to a large difference of conversion yields in the Suzuki coupling reactions. Our approach is successfully extended to other metal–Fe3O4 hybrid systems, such as those of Au and Fe3O4.11191sciescopu
Synthesis of polycrystalline Mo/MoOx nanoflakes and their transformation to MoO3 and MoS2 nanoparticles
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