Jin Hoe Kim

Morphology-selective synthesis of mesoporous SBA-15 particles over micrometer, submicrometer and nanometer scales

Mesoporous silica structures are of increasing importance as supports for enzymes and molecular organometallic catalysts. For high-surface-area, porous 3-d catalytic supports, the relationship between the exterior particle morphology and the 3-d mesopore structure is of particular significance. This paper describes the designed synthesis of selected morphologies of mesoporous SBA-15, which can be chosen from micrometer sized spheres to hundreds or tens of nanometers sized monodispersed particles such as platelets, hexagonal columns, rice-shapes, rods with tunable aspect ratios, and donuts. These are directly synthesized via control of the fundamental synthesis factors, including initial temperature, stirring rate and micelle packing parameter, rather than by the use of additives that have been generally utilized for specific morphologies in previous reports. The relationship between these basic synthesis parameters and morphologies provides insights into the formation of mesostructured materials.The SBA materials with various morphologies are expected to be useful in applications that require anisotropic or path-length-controlled diffusion.

Highly reversible conversion-capacity of MnOx-loaded ordered mesoporous carbon nanorods for lithium-ion battery anodes

An ordered mesoporous carbon (OMC) with a nanorod-shaped morphology and enhanced graphitic character was employed as an ideal support for MnOx (major phase of Mn3O4 with a small portion of MnO) nanocrystals which possess a high theoretical conversion capacity as a Li-ion battery anode. The MnOx/OMC nanocomposite was prepared by a simple wet-impregnation of Mn(NO3)2 aqueous solution onto OMC nanorods followed by thermal treatment at 450 °C in an Ar flow. The electrochemical properties of MnOx/OMC were investigated in comparison to those of bare OMC and a commercial graphite as an anode for Li-ion batteries. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction, N2 adsorption–desorption analysis, X-ray photoelectron spectroscopy, and thermogravimetric analysis revealed that 3–30 nm MnOx nanocrystals at a high loading of 68.4 wt% were formed and well dispersed in the pore structure of OMC nanorods. The MnOx/OMC exhibited a high reversible capacity (>950 mAh g−1) after 50 deep charge–discharge cycles with excellent cycling stability, Coulombic efficiency and rate capability. As an anode for Li-ion batteries, the incorporation of insulating high density MnOx nanocrystals into OMC nanorods showed synergistic benefits of high volumetric capacity as well as specific capacity, and small redox voltage hysteresis compared to OMC nanorods.

Ultrastable Pt nanoparticles supported on sulfur-containing ordered mesoporous carbonvia strong metal-support interaction

Sulfur-containing ordered mesoporous carbon (S-OMC) material was successfully obtained from a mesoporous silica template through a nano-replication method using p-toluenesulfonic acid as the framework source. The S-OMC material thus obtained could be utilized as an excellent support for Pt nanoparticles of size 3.14 nm, even though the Pt loading was 60 wt%. The Pt nanoparticles supported on the S-OMC material (Pt/S-OMC) exhibited excellent thermal stability compared with those supported on sulfur-free ordered mesoporous carbon and Vulcan carbon. XPS analysis indicated that the strong metal-support interaction between the sulfur atoms in the S-OMC support and the surface atoms of the loaded Pt nanoparticles played an important role in stabilization of the Pt nanoparticles against the Ostwald ripening process during the thermal treatments. Cyclic voltammogram results revealed that the Pt/S-OMC material exhibited reasonably high electrochemically active Pt surface areas before and after thermal treatments at 600 °C, indicating that the surface of Pt nanoparticles was not poisoned by the sulfur atoms of the S-OMC support.

Spontaneous Phase Separation Mediated Synthesis of 3D Mesoporous Carbon with Controllable Cage and Window Size

Because of their well developed porosity, high surface area, electric conductivity, high thermal conductivity, light weight, and chemical stability, porous carbon materials are of particular interest for a variety of energy-based and separation applications. [ 1 ] However, conventional microporous carbon materials, which are usually prepared by high-temperature pyrolysis followed by a physical or chemical activation process, have broad pore-size distributions mostly in the micropore ( < 2 nm) range with little control and hence suffer from critical drawbacks in advanced applications that require larger ( > 2 nm), well identifi ed, and controllable pore structures. Recent pioneering work based on nano-replication (or nano-casting) methods has enabled the successful preparations of porous carbon materials with well developed and uniform porous structures. [ 2–18 ] Inorganic templates such as zeolites, [ 5 ] ordered mesoporous silica (OMS), [ 6–10 ] colloidal silicas, [ 11–16 ] and polymer beads [ 17 , 18 ] have been employed to create uniform pore structures constructed with carbon framework. Alternatively, soft templates such as ionic surfactants and non-ionic amphiphilic block copolymers have been successfully utilized for the direct synthesis of ordered mesoporous carbon (OMC). [ 19–23 ]

Redox-buffer effect of Fe2+ ions on the selective olefin/paraffin separation and hydrogen tolerance of a Cu+-based mesoporous adsorbent

In the present work, a new mesoporous adsorbent containing ferrous/cuprous ionic species (Fe–Cu/MCM-41) has been developed for selective separation of 1-butene/n-butane. Co-impregnation of Fe2+ ions with Cu+ ions within mesopores gives superior 1-butene/n-butane separation ability. Fe–Cu/MCM-41 exhibits much higher heat of adsorption for 1-butene (−23.4 kJ mol−1) compared to that of Cu/MCM-41 (−11.2 kJ mol−1), resulting in a larger adsorption amount of 1-butene over Fe–Cu/MCM-41 (4.4 mmol g−1 at 1 atm) than that over Cu/MCM-41 (2.8 mmol g−1 at 1 atm). The results indicate that Fe–Cu/MCM-41 exhibits superior π-complexation ability for 1-butene than Cu/MCM-41. Moreover, the adsorption ability of Fe–Cu/MCM-41 does not change very much upon H2-treatment at different temperatures in the range of 273 K to 473 K, revealing the excellent hydrogen tolerance of the adsorbent. Physicochemical analyses indicated that the existence of Fe2+ species prevented the oxidation and reduction of Cu+ species during the adsorbent preparation and during the separation process in the presence of a reducing gas such as hydrogen, i.e., the Fe2+ species may act as a kind of redox buffer in the Fe–Cu/MCM-41 adsorbent for improving the chemical stability of Cu+ species that are highly effective for π-complexation with olefin.

Preparation of polypyrrole-incorporated mesoporous carbon-based composites for confinement of Eu(III) within mesopores

Mesoporous polymer-carbon composite (CMPEI/CMK-3) materials were successfully prepared by incorporation of a chelating polymer, carboxymethylated polyethyleneimine (CMPEI), into a mesoporous carbon (CMK-3) and for immobilization of Eu(III) ions, commonly used surrogates for radioactive Am(III) ions. After Eu(III) ions were loaded onto the CMPEI/CMK-3 composite, they were subsequently confined by incorporation of polypyrrole (ppy) into the mesopores of the composites. Ppy was prepared as soluble short-chain polymers using NO+ ions as oxidizing agents in a mildly acidic solution. These polymer chains were easily adsorbed on the walls of Eu-CMPEI/CMK-3 composites, efficiently immobilizing the Eu(III) ions. The use of a metal-free oxidizing agent, NO+, in mildly acidic conditions (pH 6) ensured the minimal loss of Eu(III) ions from the composites during polymerization. The resulting ppy/Eu-CMPEI/CMK-3 composites were characterized by electron microscopy, X-ray diffraction and N2 sorption analysis. The results from these characterizations commonly supported the conclusion that ppy was incorporated into the mesopores of the composites, altering the mesoporous features and reducing the pore volumes of the CMK-3 supports. Eu(III)-leaching tests showed that the presence of ppy layers in the composites could significantly improve the retention of Eu(III) ions. This study demonstrated that chelating polymer-based composites can be used for removal and long-term confinement of radioactive actinide species by properly optimizing polymer incorporation processes.

Fixation of Carbon Nanotube Within Mesoporous Titania Particles

Carbon nanotube (CNT) and mesoporous TiO2 composite (CNT/meso-TiO2) was synthesized by a nanocasting method using CNT-implanted mesoporous silica material as the template. The CNT was successfully incorporated within a mesoporous TiO2 particle, and the CNT/meso-TiO2 composite obtained exhibits a high surface area and well-established mesoporosity. Moreover, the composite material exhibits much lower electric resistance than those of mesoporous TiO2 only and physical mixture of CNT and mesoporous TiO2, which probably due to the large interface area and strong junction between the implanted CNT and TiO2 framework in the composite.