Kang Hyun Park

Hybrid gold nanoparticle-reduced graphene oxide nanosheets as active catalysts for highly efficient reduction of nitroarenes

We demonstrate a simple, one-step synthesis of hybrid gold nanoparticle–graphene oxide nanosheets (Au–GO) through electrostatic self-assembly. This method affords a facile means of controlling the effective concentration of the active Au nanoparticles on the graphene sheets, but also offers the necessary stability of the resulting Au–GO nanostructure for catalytic transformation. Furthermore, this hybrid Au–GO is successfully employed in the catalytic reduction of a series of nitroarenes with high catalytic activity. Through careful investigation of the catalyst, we find the synergistic catalytic effect of Au nanoparticles and GO, further highlighting the significance of hybrid Au–GO nanostructure. Considering the wide potential applications of a two-dimensional graphene sheet as a host material for a variety of nanoparticles, the approach developed here may lead to new possibilities for the fabrication of hybrid nanoparticle–graphene nanosheet structures endowed with multiple functionalities.

Motion of an Isolated Water Molecule within a Flexible Coordination Cage: Structural Properties and Catalytic Effects of Ionic Palladium(II) Complexes

The unique cage complexes [[(Me(4)en)Pd](3)(L)(2)](X)(6) (L = 1,3,5-tris(isonicotinoyloxyethyl)cyanurate; X(-) = BF(4)(-), ClO(4)(-)) were constructed. A single water molecule in a skeletal cage was reversibly associated and dissociated via a combination of the adequate space, polar environment, and conformational flexibility of the cage. In Suzuki-Miyaura C-C cross-coupling reactions, the cage complex showed significant catalytic activity along with the effects of the isolated single water molecule.

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.

Ordered Mesoporous Carbon Supported Colloidal Pd Nanoparticle Based Model Catalysts for Suzuki Coupling Reactions: Impact of Organic Capping Agents

Recent advances in the field of nanoscience have enabled the preparation of high‐surface‐area supported catalysts with precise control over the individual structural components. As such, a range of factors that affect the catalytic reactivity, such as the size, shape, and composition of the nanoparticles (NPs), have been identified. Herein, high‐surface‐area model catalysts that were based on colloidal Pd NPs and a hexagonally ordered mesoporous carbon support were prepared and the impact of various organic capping agents for the Pd NPs on their catalytic activity towards Suzuki coupling reactions was investigated. Colloidal Pd NPs (diameter: 3 nm) were synthesized with different organic capping agents, oleylamine (OA) and trioctylphosphine (TOP), and they were subsequently incorporated into the mesopores of CMK‐3 mesoporous carbon to yield OA‐Pd/CMK‐3 and TOP‐Pd/CMK‐3 nanocatalysts, respectively. The OA‐Pd/CMK‐3 catalyst was treated with acetic acid to generate a supported catalyst with surfactant‐free Pd NPs (OA‐Pd/CMK‐3‐A). Structural characterization revealed that the Pd NPs were uniformly dispersed throughout the mesopores of the CMK‐3 support and the particle size and crystallinity of the Pd NPs were preserved following the incorporation. All of the Pd/CMK‐3 nanocatalysts exhibited higher activity than commercial activated carbon supported Pd catalysts in Suzuki coupling reactions. The catalytic activities of the three Pd/CMK‐3 nanocatalysts were in the following order: OA‐Pd/CMK‐3‐A>OA‐Pd/CMK‐3>TOP‐Pd/CMK‐3. This result suggested that the presence and type of surfactants had a significant effect on the catalytic activity. The OA‐Pd/CMK‐3‐A catalyst also showed high activity for various substrates and good recycling ability in Suzuki coupling reactions.

Unstable Single-Layered Colloidal TiS2 Nanodisks†

Layer-structured materials are an important class of solid materials, and are especially useful as electrode materials. Usually, multilayered materials are formed by the weak interaction between the layers, which serves to stabilize the structure. The intercalation or doping into the interlamellar space of these materials enables materials scientists to tailor their physical properties. It has been suggested that the number of layers is closely related to the physical properties, thus allowing the electrical properties to be tuned by adjusting the number of layers. With the help of the accumulated synthetic knowledge, there has been special interest in monolayered materials. Although the preparation of single-layered materials including graphene is quite challenging, many studies have been conducted in an attempt to find an efficient synthetic route. There are two main ways to prepare single-layered materials; layer separation from multilayered materials or the direct synthesis of monolayered materials. In the former case, the relatively weak interaction between the layers that stabilizes the structure must be overcome. Thus, the physical separation of the layers or, more recently, the chemical functionalization of the layers, has been actively explored. In the latter case, although it is not common, there are rare reports on the direct synthesis of a monolayered structure under specialized conditions. Titanium disulfide (Figure 1) is known to form the layered structural motif (Figure 2b), in which each layer is stacked via relatively weak van der Waals interactions with its

Highly efficient and reusable copper-catalyzed N-arylation of nitrogen-containing heterocycles with aryl halides.

CuO/AB was found to be a simple and efficient catalyst for the N-arylation of a variety of nitrogen-containing heterocycles, giving the products in excellent yields.

Chemical transformation and morphology change of nickel-silica hybrid nanostructures via nickel phyllosilicates.

Ni@SiO(2) core-shell nanoparticles were transformed to Ni particles on silica spheres via a branched nickel phyllosilicate phase by hydrothermal and hydrogen reduction reactions; the final morphology was successfully employed as an active nanocatalyst for the hydrogen transfer reaction of acetophenone.

Azide-alkyne Huisgen [3+2] cycloaddition using CuO nanoparticles.

Recent developments in the synthesis of SpellECuO nanoparticles (NPs) and their application to the [3+2] cycloaddition of azides with terminal alkynes are reviewed. With respect to the importance of click chemistry, CuO hollow NPs, CuO hollow NPs on acetylene black, water-soluble double-hydrophilic block copolymer (DHBC) nanoreactors and ZnO–CuO hybrid NPs were synthesized. Non-conventional energy sources such as microwaves and ultrasound were also applied to these click reactions, and good catalytic activity with high regioselectivity was observed. CuO hollow NPs on acetylene black can be recycled nine times without any loss of activity, and water-soluble DHBC nanoreactors have been developed for an environmentally friendly process.

Gram-Scale Synthesis of Magnetically Separable and Recyclable Co@SiO2 Yolk-Shell Nanocatalysts for Phenoxycarbonylation Reactions

Co@SiO2 yolk‐shell nanostructures were fabricated on a gram scale by simple hydrogen reduction of CoO@SiO2 core‐shell nanoparticles without using an etching step. The cobalt core diameters were reduced by the lattice volume contraction of CoO to Co, forming vacancy between the cores and the silica shells. The Co@SiO2 yolk‐shell nanocatalysts were employed for the phenoxycarbonylation of iodobenzene, and exhibited high activity and reusability. The magnetic property of the cobalt cores enabled the facile separation of catalysts from the products.

Platinum-centered yolk-shell nanostructure formation by sacrificial nickel spacers.

We have synthesized Pt@silica/nickel phyllosilicate and Pt@silica yolk-shell nanostructures from NiPt@silica core-shell particles by simple chemical treatments. Silica coating of the NiPt alloy nanoparticles via the microemulsion method yielded spherical NiPt@silica core-shell nanoparticles with an average core diameter of 6.5 nm. Under a reflux condition in water, the core-shell structure transformed into Pt@silica yolk-shell nanoparticles with branched nickel phyllosilicate, which exhibited high surface area and large pore volume. The addition of hydrochloric acid selectively etched the nickel component from the NiPt cores and yielded Pt@silica yolk-shell nanoparticles with single-crystalline platinum cores. The average diameter of the metal cores was reduced to 4.5 nm. In both cases, the nickel components behaved as sacrificial spacers and successfully formed a vacancy between the metal cores and the silica hollow shells.