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Metal Hybrid Nanoparticles for Catalytic Organic and Photochemical Transformations
American Chemical Society 2015 Accounts of chemical research Vol.48 No.3
<title>Conspectus</title><P>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.</P><P>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.</P><P>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.</P><P>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.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/achre4/2015/achre4.2015.48.issue-3/ar500411s/production/images/medium/ar-2014-00411s_0010.gif'></P>
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장배관 및 고낙차를 고려한 멀티형 히트펌프 시스템의 성능특성에 관한 수치적 연구
송재선(Jaesun Song),이선일(Sunil Lee),정현준(Hyunjoon Chung),김용찬(Yongchan Kim),김성구(Sunggoo Kim) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
The performance of a multi-type heap pump system was degraded with the increases of pipe length and head when it was installed in buildings. To investigate the performance of a multi-type heat pump according to pipe length and head, a simulation model containing five modules of a compressor, evaporator, condenser, electronic expansion valve, and pipes was developed in the heating and cooling mode operation. The system was composed of one outdoor unit with a 10 HP compressor, and five indoor units. The maximum length and head of the pipe were 100 m. The simulation results showed that the system capacity was more affected by the pipe head than the length. The pipe length had less effects on the system performance in the cooling mode than that in the heating mode.
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Shin, Dongwoo,Kim, Mijong,Song, Hyunjoon Wiley-VCH 2015 Chemistry, an Asian journal Vol.10 No.8
<P>Although numerous morphologies of MnO nanostructures have been reported, an exact structural analysis and mechanistic study has been lacking. In the present study, the formation of regular MnO octapods was demonstrated in a simple procedure, comprising the thermal decomposition of manganese oleate. Because of their structural uniformity, an ideal three-dimensional model was successfully constructed. The eight arms protruded from the cubic center with tip angles of 38° and surface facets of {311} and {533} with rounded edges. The concentrations of oleate and chloride ions were the determining factors for the octapod formation. Selective coordination of the oleate ions to the {100} faces led to edge growth along the <111> direction, which was then limited by the chloride ions bound to the high-index surface facets. These structural and mechanistic analyses should be helpful for understanding the complex nanostructures and for tuning their structure-related properties.</P>
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Lee, Joongoo,Park, Ji Chan,Song, Hyunjoon WILEY-VCH Verlag 2008 Advanced Materials Vol.20 No.8
<B>Graphic Abstract</B> <P>A nanoreactor system comprising gold cores and silica hollow shells with empty inner space demonstrated. The Au@SiO<SUB>2</SUB> yolk/shell nanoreactor is synthesized by selective etching of the gold cores in Au@SiO<SUB>2</SUB> core/shell particles (see figure). This nanoreactor framework catalyzes the reduction of p-nitrophenol, exhibiting interesting size-dependent reaction property. <img src='wiley_img/09359648-2008-20-8-ADMA200702338-content.gif' alt='wiley_img/09359648-2008-20-8-ADMA200702338-content'> </P>
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Park, Garam,Lee, Chanhyoung,Seo, Daeha,Song, Hyunjoon American Chemical Society 2012 Langmuir Vol.28 No.24
<P>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<SUB>2</SUB>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.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2012/langd5.2012.28.issue-24/la300154x/production/images/medium/la-2012-00154x_0001.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la300154x'>ACS Electronic Supporting Info</A></P>
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Park, Garam,Seo, Daeha,Chung, Im Sik,Song, Hyunjoon American Chemical Society 2013 Langmuir Vol.29 No.44
<P>Gold nanoparticles with suitable surface functionalities have been widely used as a versatile nanobioplatform. However, functionalized gold nanoparticles using thiol-terminated ligands have a tendency to aggregate, particularly in many enzymatic reaction buffers containing biological thiols, because of ligand exchange reactions. In the present study, we developed a one-step synthesis of poly(ethylene glycol) (PEG)ylated gold nanoparticles using poly(dimethylaminoethyl methacrylate) (PDMAEMA) in PEG as a polyol solvent. Because of the chelate effect of polymeric functionalities on the gold surface, the resulting PEGylated gold nanoparticles (Au@P-PEG) are very stable under the extreme conditions at which the thiol-monolayer-protected gold nanoparticles are easily coagulated. Using the solvent mixture of PEG and ethylene glycol (EG) and subsequent hydrolysis, gold nanoparticles bearing mixed functionalities of PEG and carboxylate are generated. The resulting particles exhibit selective adsorption of positively charged chymotrypsin (ChT) without nonselective adsorption of bovine serum albumin (BSA). The present nanoparticle system has many advantages, including high stability, simple one-step synthesis, biocompatibility, and excellent binding specificity; thus, this system can be used as a versatile platform for potential bio-related applications, such as separation, sensing, imaging, and assays.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2013/langd5.2013.29.issue-44/la402315a/production/images/medium/la-2013-02315a_0013.gif'></P>
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Park, Youngchan,Lee, Chanhyoung,Ryu, Seol,Song, Hyunjoon American Chemical Society 2015 The Journal of Physical Chemistry Part C Vol.119 No.34
<P>The galvanic replacement reaction has recently been established as a standard protocol to create complex hollow structures with various compositions and morphologies. In the present study, the structural evolution of Ag nanocubes with Au precursors is monitored at the single-particle level by means of <I>ex situ</I> and <I>in situ</I> characterization tools. We explore two important features distinct from previous observations. First, the peak maximum of localized surface plasmon resonance (LSPR) spectra abruptly shifts at the initial stage and reaches a steady wavelength of ∼600 nm; however, the structure continuously evolves to yield a nanobox even during the late stages of the reaction. This steady wavelength results from a balance of the LSPR between the red-shift by the growth of the inner cavity and the blue-shift by the deposition of Au on the interior, as confirmed by theoretical simulations. Second, the change in morphology at different temperatures is first analyzed by both <I>ex situ</I> and <I>in situ</I> monitoring methods. The reaction at 25 °C forms granules on the surface, whereas the reaction at 60 °C provides flat and even surfaces of the hollow structures due to the large diffusion rate of Ag atoms in Au at a higher temperature. These plasmon-based monitoring techniques have great potentials to investigate various heterogeneous reaction mechanisms at the single-particle level.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2015/jpccck.2015.119.issue-34/acs.jpcc.5b05541/production/images/medium/jp-2015-05541s_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp5b05541'>ACS Electronic Supporting Info</A></P>
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