Hyunchul Oh

Metal@COFs: Covalent Organic Frameworks as Templates for Pd Nanoparticles and Hydrogen Storage Properties of Pd@COF‐102 Hybrid Material

Three-dimensional covalent organic frameworks (COFs) have been demonstrated as a new class of templates for nanoparticles. Photodecomposition of the [Pd(η(3)-C(3) H(5))(η(5)-C(5)H(5))]@COF-102 inclusion compound (synthesized by a gas-phase infiltration method) led to the formation of the Pd@COF-102 hybrid material. Advanced electron microscopy techniques (including high-angle annular dark-field scanning transmission electron microscopy and electron tomography) along with other conventional characterization techniques unambiguously showed that highly monodisperse Pd nanoparticles ((2.4±0.5) nm) were evenly distributed inside the COF-102 framework. The Pd@COF-102 hybrid material is a rare example of a metal-nanoparticle-loaded porous crystalline material with a very narrow size distribution without any larger agglomerates even at high loadings (30 wt %). Two samples with moderate Pd content (3.5 and 9.5 wt %) were used to study the hydrogen storage properties of the metal-decorated COF surface. The uptakes at room temperature from these samples were higher than those of similar systems such as Pd@metal-organic frameworks (MOFs). The studies show that the H(2) capacities were enhanced by a factor of 2-3 through Pd impregnation on COF-102 at room temperature and 20 bar. This remarkable enhancement is not just due to Pd hydride formation and can be mainly ascribed to hydrogenation of residual organic compounds, such as bicyclopentadiene. The significantly higher reversible hydrogen storage capacity that comes from decomposed products of the employed organometallic Pd precursor suggests that this discovery may be relevant to the discussion of the spillover phenomenon in metal/MOFs and related systems.

Highly Effective Hydrogen Isotope Separation in Nanoporous Metal–Organic Frameworks with Open Metal Sites: Direct Measurement and Theoretical Analysis

Separating gaseous mixtures that consist of very similar size is one of the critical issues in modern separation technology. Especially, the separation of the isotopes hydrogen and deuterium requires special efforts, even though these isotopes show a very large mass ratio. Conventionally, H/D separation can be realized through cryogenic distillation of the molecular species or the Girdler-sulfide process, which are among the most energy-intensive separation techniques in the chemical industry. However, costs can be significantly reduced by using highly mass-selective nanoporous sorbents. Here, we describe a hydrogen isotope separation strategy exploiting the strongly attractive open metal sites present in nanoporous metal-organic frameworks of the CPO-27 family (also referred to as MOF-74). A theoretical analysis predicts an outstanding hydrogen isotopologue separation at open metal sites due to isotopal effects, which has been directly observed through cryogenic thermal desorption spectroscopy. For H2/D2 separation of an equimolar mixture at 60 K, the selectivity of 12 is the highest value ever measured, and this methodology shows extremely high separation efficiencies even above 77 K. Our theoretical results imply also a high selectivity for HD/H2 separation at similar temperatures, and together with catalytically active sites, we propose a mechanism to produce D2 from HD/H2 mixtures with natural or enriched deuterium content.

Exploiting Diffusion Barrier and Chemical Affinity of Metal–Organic Frameworks for Efficient Hydrogen Isotope Separation

Deuterium plays a pivotal role in industrial and scientific research, and is irreplaceable for various applications such as isotope tracing, neutron moderation, and neutron scattering. In addition, deuterium is a key energy source for fusion reactions. Thus, the isolation of deuterium from a physico-chemically almost identical isotopic mixture is a seminal challenge in modern separation technology. However, current commercial approaches suffer from extremely low separation efficiency (i.e., cryogenic distillation, selectivity of 1.5 at 24 K), requiring a cost-effective and large-scale separation technique. Herein, we report a highly effective hydrogen isotope separation system based on metal-organic frameworks (MOFs) having the highest reported separation factor as high as ∼26 at 77 K by maximizing synergistic effects of the chemical affinity quantum sieving (CAQS) and kinetic quantum sieving (KQS). For this purpose, the MOF-74 system having high hydrogen adsorption enthalpies due to strong open metal sites is chosen for CAQS functionality, and imidazole molecules (IM) are employed to the system for enhancing the KQS effect. To the best of our knowledge, this work is not only the first attempt to implement two quantum sieving effects, KQS and CAQS, in one system, but also provides experimental validation of the utility of this system for practical industrial usage by isolating high-purity D2 through direct selective separation studies using 1:1 D2/H2 mixtures.

Facile Synthesis Tool of Nanoporous Carbon for Promising H2, CO2, and CH4 Sorption Capacity and Selective Gas Separation

The commercialization of hydrogen as a clean source of energy is a vital requirement for overcoming the anticipated energy crisis. In addition, the capture of CO2 and commercialization of methane as an efficient and clean alternative to polluting gasoline are important goals. To this end, we have developed a nanoporous activated carbon material prepared from renewable resources that has a high storage capacity for various gases. Sugar beet leaves were converted to graphite flakes and decorated with polymer nanoparticles, giving rise to a highly porous activated carbon through chemical activation. The developed porous carbon has a high surface area (2800 m2 g−1) and specific pore volume (1.86 cm3 g−1), as well as high nitrogen and oxygen contents. The combination of high surface area, pore volume, and nitrogen and oxygen contents provided superior storage capacity for various gases. The total hydrogen storage capacities at 20 bar were 5.9 and 0.15 wt% at 77 and 298 K, respectively. In addition, the physical upper limit of hydrogen storage capacity was also evaluated using Brunauer–Emmett–Teller isotherms at the liquefaction temperature of hydrogen (20 K). A value of 14.1 wt% was obtained, which is the highest reported value for a porous carbon. The CO2 capture and CH4 storage capacities at room temperature and 20 bar were 19.65 and 7.6 mmol g−1, respectively, which are also among the highest values reported for porous carbon materials. Furthermore, the separation selectivity for CO2/CH4 binary mixtures was evaluated based on the ideal adsorbed solution theory (IAST) model and found to be 4.6.

A Review of Anodic TiO 2 Nanostructure Formation in High-temperature Phosphate-based Organic Electrolytes: Properties and Applications

In the present review, we provide an overview of the research trend of anodic TiO2 nanostructures. To date, most anodic TiO2 nanostructure formation has focused on the fluoride ion electrolyte system to form nanotube layers. Recently, a novel approach that describes the formation of thick, self-organized TiO2 nanostructures was reported. These layers can be prepared on Ti metal by anodization in a hot organic/K2HPO4 electrolyte. This nanostructure consists of a strongly interlinked network of nanosized TiO2, and thus provides a considerably higher specific surface area than that of using anodic TiO2 nanotubes. This review describes the formation mechanism and novel properties of the new nanostructures, and introduces potential applications.

A Study on the Efficient Management of Volunteer Fire Department

The purpose of this study is to investigate the influence of organizational culture to the activities satisfaction of volunteer firefighter. For that, we surveyed 182 volunteer firefighters worked in Sejong city. The survey was analyzed the reliability in questionnaire design by SPSS 20.0 win program. The interrelationship of each factors were confirmed by analysis of frequency, percentage and regression analysis. The regression analysis was performed in order to investigate effects of group, development, hierachy, and rationality culture based organizational culture on activities satisfaction of volunteer firefighter. A factor of group and development culture in organizational culture was found to be a positive influence on the activities satisfaction of the volunteer firefighter under significance probability of < 0.05. The bigger group and development culture the volunteer fire department, the higher the activities satisfaction of the volunteer firefighter. This paper is expected to serve as a basis for the efficient operation of the volunteer fire department in Korea.