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
Functional Materials for Biophysics, Polymer, and CCS
"Coffee-Ring Effect" is a well-known phenomenon for the characteristic ring-like deposit along the perimeter of a spill of coffee. The driving force of the pattern is capillary flow induced by the differential evaporation rates across the drop. Suppression of the coffee-ring effect has attracted great research interest in broad modern industries such as inkjet printing, functional coating, color filter, and DNA chips. In this study, we have developed a simple and novel method for avoiding coffee-ring structure by changes in the force balance between viscosity and Marangoni effect. We are also focusing on developing new absorbents for separating CO2 from mixture gas streams. The following new emerging research topics are in progress in our laboratory.
Suppression of coffee-ring effect by controlled hydrophobic interactions
Phase-changing absorbents for CO2 removal
3D printing polymer materials combined with the recycled wood compounds
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 at POSTECH
Solid-state 13C CP/MAS NMR spectroscopy: KAIST and Korea Basic Science Institute
Rubotherm (for hydrogen storage): Hanwha Chemicals and Korea Institute of Energy Research
XRD Rietveld refinement: Dr. Y. Lee (Yonsei University) and Dr. S. Takeya (AIST)
Thermodynamic model: Predictive Soave-Redlich-Kwong (PSRK) model for gas hydrate equilibrium calculation