Jae Eui Yie

Reversible replication between ordered mesoporous silica and mesoporous carbon

Highly ordered mesoporous silica can be regenerated from a mesoporous carbon CMK-3 that is a negative replica of mesoporous silica SBA-15, indicating reversible replication between carbon and inorganic materials.

Systematic phase control of periodic mesoporous organosilicas using Gemini surfactants

Highly ordered periodic mesoporous organosilica (PMO) materials with various mesostructures, including lamellar, bicontinuous cubic Ia3d, 2D hexagonal (P6mm), 3D hexagonal (P63/mmc) and cubic Pm3n, have been synthesized using Gemini surfactants with general formulas of [CnH2n+1N(CH3)2(CH2)sN (CH3)2CnH2n+1]Br2 (n = 6–18 and s = 3–12, Cn-s-n). The nature of the Gemini surfactant such as alkyl chain length (n) and spacer length (s), and the synthetic conditions such as reaction temperatures and molar compositions are controlling parameters for desired mesostructures. The PMO materials, synthesized at room temperature from Cn-6-n, exhibit phase transition from lamellar to bicontinuous cubic Ia3d, 2D hexagonal, 3D hexagonal and cubic Pm3n as the chain length decreases, whereas only the lamellar and 2D hexagonal PMO materials with different lattice parameters depending on the chain length are obtained at high reaction temperature (373 K). The Cn-8-n and Cn-10-n surfactants also yield 2D hexagonal PMO material in a very wide range of synthetic condition at 373 K. The PMO materials with various mesostructures thus obtained exhibit high BET surface areas in the range of 900–1500 m2 g−1 and total pore volumes of about 0.5–1.4 cm3 g−1.

Simple and fast microwave-enhanced wet etching of SiC particles for electroless Ni-P plating

A simple and fast microwave-enhanced wet chemical etching process of SiC particles has been developed for electroless Ni-P plating, and the etching effects are investigated by using BET surface area analysis, SEM, XPS and XAFS. The results indicate that the microwave etching for only 30 s gives the formation of surface oxide species, which leads to an increase in BET surface area of the SiC sample. The modified SiC surfaces are suitable for the electroless Ni-P plating and the deposit exhibits excellent chemical and mechanical adhesion strength. The etching technique, developed in the present work, will be a very useful tool for the preparation of composite materials between SiC particles and metal matrix.

Direct synthesis of ordered mesoporous materials constructed with polymer-silica hybrid frameworks

Highly ordered mesoporous materials constructed with integrated polymer-silica hybrid frameworks can be obtained via a one-step synthetic strategy using a mixture of polymer and silicate as the framework sources in the presence of a structure-directing agent.

Synergism and kinetics in CO oxidation over palladium-rhodium bimetallic catalysts

The activity and kinetics of CO oxidation over alumina-supported Pd-Rh bimetallic catalysts were investigated. One bimetallic catalyst, Pd-Rh(2), was prepared by two-step impregnation and another, Pd-Rh(l), by simultaneous impregnation. Monometallic catalysts as well as a physical mixture of them were also prepared. The catalysts were characterized by selective chemisorption of both H2 and CO, and an attempt was made to determine the surface compositions of the bimetallic catalysts. The bimetallic catalysts showed different kinetic behavior, such as higher turnover frequencies (TOFs), lower apparent activation energies and/or negative reaction orders for CO which were smaller in the absolute value, from that of the monometallic catalysts as well as a physical mixture of them. It is suggested that this Pd-Rh synergism is due to an interaction on the catalyst surface, such that adsorbed CO or oxygen on one metal migrates to the other metal site so that the reaction rate is facilitated and also that the particles of Pd and Rh are located close enough to each other for the interaction to occur. On the surface of Pd-Rh (2) most of the Pd and Rh particles existed as separate entities, while a great portion of the particles on Pd-Rh(l) exhibited the surface enrichment of Pd. This explains the higher TOF and the negative reaction orders for CO over Pd-Rh(2) which were smaller in the absolute value than those over Pd-Rh(l).

Rational design of ordered mesoporous carbon with controlled bimodal porosity via dual silica templating route

Combining both nano-replication and nano-imprinting techniques using dual silica templates provides a simple way to synthesize ordered mesoporous carbons with bimodal pore size distributions ( approximately 1.5 nm and approximately 3.5 nm).

Regeneration of mesoporous inorganic materials using ordered mesoporous carbon as the template

Abstract Regeneration of mesoporous inorganic materials from ordered mesoporous carbons has been successfully performed in the present work. A mesoporous silica SBA-15 are used as a template for the synthesis of the mesoporous carbon CMK-3. Subsequently, mesoporous inorganic replica materials can be obtained from the mesoporous carbon. This synthetic principle is very useful for the preparation of various kinds of the mesoporous inorganic materials.

An XANES study of carbides of molybdenum and tungsten

The X-ray absorption near edge structure (XANES) of molybdenum and tungsten compounds has been studied by using synchrotron radiation. Substantial difference in XANES features between metals and their carbides suggested significant difference in electronic structure between them. The shift in edge position indicated charge transfer from metal to carbon when a carbide is formed. In light of a modern band theory, the larger white line areas for carbides could be interpreted as due to some of the unoccupied d-states which are not measured by x-ray white line area.

Effect of multivalent cations on agglomeration of Ru clusters supported on Y zeolite

The effect of multivalent cations, Ca2+, Ba2+, Y3+, Ce3+ and La3+ on the agglomeration of Ru clusters on NaY zeolite under oxygen and at high temperature has been investigated with 129Xe NMR spectroscopy and X-ray absorption fine structure. Multivalent metal cations exchanged into the zeolite suppress neither the migration nor agglomeration of small Ru clusters inside the supercage of NaY zeolite into large metal particles onto the external surface of NaY zeolite under 1 atm oxygen above 520 K. However, the resultant Ru particle size depends on the type of metal cations exchanged into NaY zeolite.

The Improvement of Chemical and Mechanical Properties of Al/Cu-Coated SiC Composites

The effect of a microwave-enhanced wet chemical etching process of SiC particles on the electroless copper plating and on the Al/Cu-coated SiC composites was investigated. The microwave-enhanced wet etching process increased the concentration of surface oxides on SiC. The BET surface area of SiC increased, reached its maximum value at 30 s, and then decreased during an etching process. The enhanced chemical adhesion strength between the coated copper and SiC was observed after an etching process. Furthermore, the sintering density and transverse rupture strength (TRS) of Al/Cu-coated SiC composites were improved when SiC particles were etched. This result indicated that the microwave-enhanced etching of SiC particles also improved chemical and mechanical adhesion of Al/Cu-coated SiC composites.