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Šwp˜_•¶ 2012

Size Control of Ni Nanocluster by the Carbon Chain Length of Secondary Alkoxide

H. Kitagawa, N. Ichikuni*, T. Hara, S. Shimizu, S. Xie, T. Tsukuda
e-J. Surf. Sci. Nanotech., 10, 648-650 (2012).

Secondary-alkoxide stabilized Ni colloid was synthesized using secondary alkoxide as a reducing and stabilizing agents. Cluster size was controlled by changing carbon chain length of secondary alkoxide; 2-octanol derived alkoxide gave the smallest nanocluster. Ni colloid thus prepared was applied to the preparation of supported Ni nanocluster catalysts. Size dependency of Ni nanocluster on catalytic activity for water gas shift reaction was observed.

A New Binding Motif of Sterically Demanding Thiolates on a Gold Cluster

Jun-ichi Nishigaki, Risako Tsunoyama, Hironori Tsunoyama, Nobuyuki Ichikuni, Seiji Yamazoe, Yuichi Negishi, Mikinao Ito, Tsukasa Matsuo, Kohei Tamao, and Tatsuya Tsukuda*
J. Am. Chem. Soc.134, 14295-14297 (2012).

A gold cluster, Au41(S-Eind)12, was synthesized by ligating bulky arenethiol (Eind-SH) to preformed Au clusters. EXAFS, XPS, and fragmentation pattern in the mass analysis indicate that formation of gold-thiolate oligomers at the interface is suppressed in sharp contrast to conventional thiolate-protected Au clusters.


Enhancement in Aerobic Alcohol Oxidation Catalysis of Au25 Clusters by Single Pd Atom Doping

S. Xie, H. Tsunoyama, W. Kurashige, Y. Negishi, T. Tsukuda*
ACS Catal., 2, 1519-1523 (2012)

Au25 and Pd1Au24 clusters on multiwalled carbon nanotubes were developed via adsorption of Au25(SC12H25)18 and Pd1Au24(SC12H25)18, respectively, on the nanotubes, followed by calcination. Comparison of their catalysis for the aerobic oxidation of benzyl alcohol showed that single Pd atom doping significantly improved the catalytic performance of Au25 for the first time.

Synthesis and the Origin of the Stability of Thiolate-Protected Au130 and Au187 Clusters

Y. Negishi*, C. Sakamoto, T. Ohyama, T. Tsukuda
J. Phys. Chem. Lett., 3, 1624-1628 (2012)

Two stable thiolate-protected gold clusters (Au:SR), Au130 and Au187 clusters, were synthesized to obtain a better understanding of the size dependence of the origin of the stability of Au:SR clusters. These clusters were synthesized by employing different preparation conditions from those used to synthesize previously reported magic gold clusters; in particular, a lower [C12H25SH] to [AuCl4] molar ratio ([AuCl4]:[RSH] = 1:1) was used than that used to prepare Au25(SR)18, Au38(SR)24, Au68(SR)34, Au102(SR)44, and Au144(SR)60 (id. = 1:4-12). The two clusters thus synthesized were separated from the mixture with a high resolution by high-performance liquid chromatography with reverse-phase columns. Mass spectrometry of the products revealed the presence of two clusters with chemical compositions of Au130(SC12H25)50 and Au187(SC12H25)68. The origin of the stability of these two clusters and the size dependence of the origin of the stability of thiolate-protected gold clusters were discussed in terms of the total number of valence electrons.

Stabilized Gold Clusters: from Isolation Toward Controlled Synthesis

Prasenjit Maity, Songhai Xie, Miho Yamauchi and Tatsuya Tsukuda*
Nanoscale, 4, 4027-4037 (2012) 

Bare metal clusters with fewer than ~100 atoms exhibit intrinsically unique and size-specific properties, making them promising functional units or building blocks for novel materials. To utilize such clusters in functional materials, they need to be stabilized against coalescence by employing organic ligands, polymers, and solid materials. To realize rational development of cluster-based materials, it is essential to clarify how the stability and nature of clusters are modified by interactions with stabilizers by characterizing isolated clusters. The next stage is to design on-demand function by intentionally controlling the structural parameters of cluster-based materials; such parameters include the size, composition, and atomic arrangement of clusters and the interfacial structure between clusters and stabilizers. This review summarizes the current state of isolation of gold clusters stabilized in various environments and surveys ongoing efforts to precisely control the structural parameters with atomic level accuracy.

Preparation and Catalysis of Supported NiO Nanocluster for Oxidative Coupling of Thiophenol

Nobuyuki Ichikuni*, Osamu Tsuchida, Jun Naganuma, Takayoshi Hara, Hironori Tsunoyama, Tatsuya Tsukuda and Shogo Shimazu
Trans. MRS-J , 37, 177-180 (2012).

Supported NiO nanocluster was prepared by using Ni colloid. Alkoxide stabilized Ni nanocluster supported on SiO2 was oxidized by exposing to air at room temperature to produce NiO nanocluster. The cluster size of NiO was estimated by XAFS analysis. Supported NiO nanocluster thus prepared showed the catalytic activity for oxidative coupling of thiophenol, whereas the conventional impregnation NiO catalyst did not. Remarkable NiO cluster size dependency on activity for oxidative coupling of thiophenol was observed.

Size and Shape of Nanoclusters: Single-shot Imaging Approach

Y. Han, D.S. He, Y. Liu. S. Xie, T. Tsukuda, Ziyou Li*
Small 8, 2361-2364 (2012)

A method of single shot imaging via aberration corrected scanning transmission electron microscopy equipped with high angle annular dark-field detector (STEM-HAADF) has been applied to size-selected gold model catalysts (Au25 and Au39) on hydroxyapatite. Through quantitative intensity analysis the size, in terms of number of atoms as well as 3D shape of the clusters are obtained.

Selective Synthesis of Organogold Magic Clusters Au54(CßCPh)26

Prasenjit Maity, Tomonari Wakabayashi, Nobuyuki Ichikuni, Hironori Tsunoyama, Songhai Xie, Miho Yamauchi, and Tatsuya Tsukuda*
Chem. Commun. 48, 6085-6087 (2012) Selected as front cover of Chem. Commun.

Organogold culusters Au54(C2Ph)26 were selectively synthesized by reacting polymer-stabilized Au clusters (1.2}0.2 nm) with excess phenylacetylene in chloroform.

Platonic Hexahedron Composed of Six Organic Faces with an Inscribed Au Cluster

Masanori Sakamoto, Daisuke Tanaka, Hironori Tsunoyama, Tatsuya Tsukuda, Yoshihiro Minagawa, Yutaka Majima, and Toshiharu Teranishi*
J. Am. Chem. Soc., 134 (2), 816-819 (2012)

The structures of nanomaterials determine their individual properties and the suprastructures they can form. Introducing anisotropic shapes and/or interaction sites to isotropic nanoparticles has been proposed to extend the functionality and possible suprastructure motifs. Because of symmetric anisotropy, Platonic solids with regular polygon faces are one of the most promising nanoscale structures. Introduction of Platonic solid anisotropy to isotropic nanomaterials would expand the functionality and range of possible suprastructure motifs. Here, we demonstrate a novel strategy to obtain nano-Platonic solids through the face coordination of square porphyrins on an inscribed Au sphere with adequate size. The face coordination of the multidentate porphyrin derivatives, with four acetylthio groups facing the same direction, on the Au cluster encased the Au cluster in a Platonic hexahedron with six porphyrin faces. Transmission electron microscopy, mass spectrometry, elemental analysis, and scanning tunnelling microscopy were used to confirm the formation of the nano-Platonic hexahedron.

Study of the Structure and Electronic State of Thiolate-protected Gold Clusters by Means of 197Au Mössbauer Spectroscopy

N. Kojima*, K. Ikeda, Y. Kobayashi, T. Tsukuda, Y. Negishi, G. Harada, T. Sugawara, M. Seto
Hyperfine Interactions, 207 (1-3), 127-131(2012)

We have investigated the structures and electronic states of a series of glutathionate-protected Au clusters, Aun(SG)m with n = 10 - ~55, using 197Au Mössbauer spectroscopy, which allows us to probe the local environment of the constituent Au atoms via isomer shift (IS) and quadrupole splitting (QS). The spectral profile abruptly changes on going from Au22(SG)17 to Au25(SG)18, then it smoothly changes to that of Au55(SG)m. However, the spectral profile dramatically changes on going from Au55(SG)m to the dodecanethiolate-protected Au cluster with average diameter of 2 nm. The 197Au Mössbauer spectra of glutathionate-protected Au clusters and dodecanethiolate-protected Au clusters were successfully analyzed on the basis of the structure and electronic state of Au25(SG)18.

Thermal Stabillization of Thin Gold Nanowires by Surfactant-Coating: A Molecular Dynamic Study

S. E. Huber*, C. Warakulwit, J. Limtrakul, T. Tsukuda, M. Probst
Nanoscale, 4, 585-590 (2012)

The thermal stabilization of thin gold nanowires with a diameter of about 2 nm by surfactants is investigated by means of classical molecular dynamics simulations. While the well-known melting point depression leads to a much lower melting of gold nanowires compared to bulk gold, coating the nanowires with surfactants can reverse this, given that the attractive interaction between surfactant molecules and gold atoms lies beyond a certain threshold. It is found that the melting process of coated nanowires is dominated by surface instability patterns,whereas the melting behaviour of gold nanowires in a vacuum is dominated by the greater mobility of atoms with lower coordination numbers that are located at edges and corners. The suppression of the melting by surfactants is explained by the isotropic pressure acting on the gold surface (due to the attractive interaction) which successfully suppresses large-amplitude thermal motions of the gold atoms.

Toward an Atomic-Level Understanding of Size-Specific Properties of Protected and Stabilized Gold Clusters

Tatsuya Tsukuda*
Bull. Chem. Soc. Jpn., 85 (2), 151-168 (2012)

Metal clusters consisting of fewer than 100 atoms (diameter < 2 nm) are highly promising as a new class of building units for functional materials because of their novel and size-dependent properties. Nevertheless, basic and applied studies of metals clusters have been hampered by the lack of specific guidelines for design and precise synthetic methods. This account surveys recent investigations of gold clusters focusing on our effort toward an atomic-level understanding and control of their size-specific properties. We have developed a size-controlled method for synthesizing gold clusters protected by ligands, stabilized by polymers, and supported on solids. Remarkable size-effects on stabilities and various properties including catalysis were observed. Their mechanisms are discussed based on fundamental knowledge of bare gold clusters in the gas phase.


High-yield Synthesis of PVP-stabilized Small Pt Clusters by Microfluidic Method

M. Jakir Hossain, Hironori Tsunoyama, Miho Yamauchi, Nobuyuki Ichikuni, Tatsuya Tsukuda*
Catal. Today, 183, 101-107 (2012).
*Selected as featured article in Chemical Engineering of Advances in Enginerring

Monodisperse PVP-stabilized Pt nanoparticles (PtNPs) with an average diameter of 1.4 } 0.3 nm were efficiently produced via the complete reduction of Pt4+ ions by BH4 in a micromixer. Because of microfluidic mixing, hydrolytic decomposition of BH4- by the PtNPs formed in the initial stage of the reaction was suppressed, and hence, the PtNP yield was higher than that in the conventional batch mixing. The results of various spectroscopic analyses including EXAFS, FTIR of CO and XPS revealed that the microfluidically synthesized PtNPs were negatively charged and had a high population of edges and vertices on their surface. The PtNPs dispersed in oxygen-saturated water catalyzed the selective oxidation of PhCH2OH to PhCHO.

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