Research

Synthesis of Clathrate Compounds

Clathrates are crystalline inclusion compounds stabilized by physical interactions between host species and relatively small guest molecules contained in the cages of the host framework. Clathrate compounds have been recognized as potential energy storage or gas separation media because they can store a large fraction of gas per unit volume of the solid phase. Hydroquinone, phenol, and Dianin’s compounds are widely known to form organic clathrates, and they are the basis for an extensively studied class of inclusion compounds. In this study, we prepare organic, organic-inorganic, and organic-carbon hybrid clathrates by the gas-phase reaction between host and guest molecules or recrytallization in solutions. The crystal structure of clathrate compounds is analyzed by the X-ray diffraction and refinements. The occupation of guest molecules in the cages can be confirmed using a customized Raman spectroscopy and solid-state 13C NMR. In some cases, for practical applications, we measure the storage capacity of guest components in the framework by the elementary analysis or the direct release method. Pressure- and/or temperature-induced structural transformations of clathrates and dynamic release of guest molecules from the framework are also observed using the synchrotron X-ray diffraction with diamond anvil cells (DACs), terahertz (THz) time-domain spectroscopy, and in situ Raman spectroscopy combined with a temperature-controlled Linkam stage.

Applications of Gas Hydrate Technology

Gas hydrates (or clathrate hydrates) are also clathrate compounds in which the host molecule is water and the guest molecule is typically a gas or liquid. In physical appearance, gas hydrates resemble packed snow or ice. It is interesting to note that, under pressure, they can exist at temperatures significantly above the freezing point of water. Fundamental understanding of gas hydrate properties and formation and decomposition process is critical in many energy and environmental areas. For practical applications of gas hydrate, considerable knowledge regarding thermodynamic stability, structural identification, and cage occupancy of guests of gas hydrates would be of particular importance. We have studied several applications of gas hydrate technology as follows:

- Natural gas hydrate (NGH) for gas storage and transportation
- Gas separation

- Water treatment
- Desalination
- Refrigeration

Theoretical Studies (DFT Calculations & MD Simulations)

Theoretical simulations, including density functional theory (DFT) and molecular dynamics (MD), are essential tools for providing molecular-level insights into the structural and thermodynamic properties of complex materials. In our laboratory, we utilize these computational approaches to deeply understand host-guest interactions, structural stability, and phase transition kinetics in various systems such as gas hydrates, solid organic clathrates, and metal-organic frameworks (MOFs). By exploring microscopic behaviors like cooperative molecular ordering and diffusion, we bridge the gap between atomistic phenomena and experimental observations. We have applied theoretical simulations to study several areas as follows:

Molecular-level mechanisms of gas hydrate formation and desalination
Host-guest interactions and binding energy estimation in clathrate compounds
Ion exclusion and molecular diffusion behaviors in aqueous solutions
Gas separation and storage in porous structures (e.g., MOFs, HOFs)
Thermodynamic stability under varying pressure and temperature conditions

Experimental Facilities

In situ Raman spectroscopy

Nd:YAG Laser emitting a 532 nm
Power of 150 mW
Single monochromator of 1800 grooves/mm grating
SpectraPro 2500i, 500mm spectrograph system
PI Acton PIXIS:100B digital CCD detector
Olympus BX51 microscope frame
Temperature control with the Linkam stage
Advanced measurements with DAC and equilibrium cell

Powder X-ray diffraction (XRD)

SmartLab, RIGAKU
Target : Cu
Maximum rated output : 3 kW
Goniometer minimum step size : 0.0001°
Goniometer maximum slew speed : 500°/min
Scan speed : 0.02°/min ~ 40°/min
Step width : 0.0002° ~ 10°

Diamond anvil cell (DAC)

Standard symmetric system
100 ~ 400 μm culet diamond anvils
Pressure measurement by the ruby fluorescence method
Ultra high pressure experiments up to ~ 20 GPa

Fourier transform infrared spectroscopy (FTIR)

Nicolet iS 5
EverGlo™ mid IR source
Single bounce ATR kit
Electromagnetic interferometer
KBr/Ge coated beamsplitter
DLaTGS detector
Diode laser
OMNIC 8 Software (Sigma & Aldrich Libraries)

Terahertz time-domain spectroscopy (THz-TDS)

Reference spectrum bandwidth: 0.1 ~ 4 THz
Signal to noise ratio: > 10,000:1
Maximum THz amplitude: ~10 nA
Sample diameter: 3 ~ 50 mm
Temperature range: 77 K (LN2) ~ 450 K
Designed and operated by Prof. T.-I. Jeon (KMOU)

Other measurements and analysis

- Synchrotron X-ray diffraction: Pohang Accelerator Laboratory (PAL) at POSTECH
- Solid-state 129Xe and 13C CP/MAS NMR spectroscopy: Korea Basic Science Institute (KBSI)
- Rubotherm (for hydrogen storage): Hanwha Chemicals and Korea Institute of Energy Research
- XRD Rietveld refinements: FullProf and GSAS
- Materials Studio (BIOVIA), GROMACS and LAMMPS
- Thermodynamic model: Predictive Soave-Redlich-Kwong (PSRK) model for gas hydrate equilibrium calculation

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