Ung Su Choi

Korea Institute of Science and Technology, Seoul, Seoul, South Korea

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Publications (38)106.43 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A facile strategy is successfully developed for the centimeter-scale preparation of hierarchically porous aminosilica monolith as a CO2 adsorbent just by simple processes of solvent-evaporation-induced coating, self-assembly, and concentration of tetraethyl orthosilicate sol on the surface of a polymer foam template without any adhesive composite material or hydrothermal treatment. (3-Aminopropyl) trimethoxysilane is immobilized on the surface of silica monolith via a gas-phase procedure. The silica frameworks of the monolith mimic those of the polymer foam template at the macroscale, and the frameworks are composed of the SBA-15 structure at the nanoscale. The hierarchically porous structure demonstrates improved properties over the single-mode porous component, with the macroporous framework ensuring mechanical stability and good mass transport properties, while the smaller pores provide the functionality for CO2 adsorption.
    ACS Applied Materials & Interfaces 07/2014; · 5.01 Impact Factor
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    ABSTRACT: Herein, the mixing effect of amine and carboxyl groups on electrorheological (ER) properties has been presented with the chitosan and alginic acid dispersed suspensions. Chitosan (for the amine group) and alginic acid (for the carboxyl group) are used to investigate the mixing effect of the amine and carboxyl groups on ER properties with the control of their mixing ratio in the silicone oil. The surface-chemical structure of the mixture of the chitosan and alginic acid particles in the silicone oil is demonstrated by in situ Fourier transform infrared (FT-IR) spectroscopy at various electric fields for the first time. This study focuses on whether the mixture of chemical groups in the ER fluid can promote ER properties or not, and in situ FT-IR analysis of the interface between ER particles in the silicone oil at various DC electric fields. The ER fluids exhibited the increase of the yield stress values with the increase of the counter group addition up to the weight ratio of 50 : 50 (chitosan : alginic acid). A noteworthy result is that the mixing effect of the amine and carboxyl groups resulting in enhanced ER properties is clearly proved. In the in situ FT-IR study, the complex form of amine and carboxyl groups of particles in the ER fluid was confirmed under the electric field.
    Physical Chemistry Chemical Physics 08/2013; · 3.83 Impact Factor
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    ABSTRACT: A novel method for Cu(2+) sequestration in Cu(2+) aqueous solution has been demonstrated using amine-functionalized double-walled silica nanotubes (DWSNTs). Herein, the precipitation method and the adsorption method are combined to remove Cu(2+) in the Cu(2+) aqueous solution. Primary (1°), secondary (2°), tertiary (3°), di-, tri-amines are immobilized on the surface of DWSNT as the adsorption site. The results show that the Cu(2+) adsorption amount on the amine-functionalized DWSNTs is in the following order: tri-amine>di-amine>1° amine>2° amine>3° amine. The complexed Cu(2+)s with the amine-functionalized DWSNTs become Cu(OH)2 crystals due to the reaction with OH(-)s dissociated from water. Thus, the amine-functionalized DWSNTs show the superior sequestration capacity of Cu(2+) in the Cu(2+) aqueous solution owing to the Cu(OH)2 crystals growth on them. FT-IR, FEG-SEM, HR-TEM, and XRD studies demonstrate the mechanism of the Cu(2+) adsorption and the Cu(OH)2 crystals growth. The crystallization-technique of the heavy metal ion on the amine-functionalized DWSNTs is also expected to have potential applications such as the facile synthesis of nano- and microparticles, and the metal catalyst supporter.
    Journal of hazardous materials 06/2013; 260C:489-497. · 4.14 Impact Factor
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    ABSTRACT: Novel silica support has been required for high amine loading and good CO(2) molecule diffusion into its pores to increase the performance of CO(2) adsorbents. Herein, amine groups supported on double-walled silica nanotubes (DWSNTs) have been prepared via the immobilization of various aminosilanes (primary, secondary, tertiary, di-, and tri-aminosilanes) on DWSNT, and found to be a very effective adsorbent for CO(2) capture. Amine groups immobilized DWSNTs captured CO(2) reversibly in a temperature swing process at various adsorption temperatures (25°C, 50°C, 75°C, and 100°C). The amines on modified DWSNTs showed high CO(2) capture capacity in the order of tri-, di-, primary, secondary, and tertiary amines. The CO(2) capture capacity of all aminosilanes immobilized DWSNTs decreased linearly with the increase of the adsorption temperature. We expect that DWSNT would be able to inspire researchers to use it not only as a support for CO(2) capture but also as a promising candidate for various applications.
    Journal of hazardous materials 02/2013; 250-251C:53-60. · 4.14 Impact Factor
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    ABSTRACT: Electrorheological (ER) effects of alginic acid and alginate salts (Na+ alginate, NH4+ alginate, and Ca2+ alginate) dispersed suspensions were investigated under DC electric fields. A noteworthy result is that the Ca2+ alginate dispersed suspension showed negative electrorheological effects under electric fields while the other suspensions exhibited positive electrorheological effects. It is the first time that the negative ER effect is obtained with the biomacromolecule. Interestingly, at the DC electric fields, the electromigration of particles to two electrodes was observed in the negative ER fluid, while the particles-bridges formed between two electrodes in the case of the positive ER fluid. In conclusion, the specific salt type of biomacromolecules could be suitable ER particles for negative ER suspension. We believe that our study can present a new way for the development of the biocompatible and eco-friendly negative ER fluids.
    ACS Applied Materials & Interfaces 01/2013; · 5.01 Impact Factor
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    ABSTRACT: Herein, the electrorheological (ER) properties of highly dispersion-stable, biocompatible and biodegradable chitosan derivative dispersed ER suspensions are explored. Electro-mechanical responses of the ER suspensions are enhanced with fixed spacers (amide and ester groups) and various functional groups (acid series and their complex forms with urea). A noteworthy result is that the shear stress of urea complexed chitosan acid dispersed suspensions was higher than before doping the urea molecule. However, urea complexed chitosan phosphate and sulphate showed a decreased tendency of shear stress due to too high conductivity at the high temperature. In the dispersion stability test, the chitosan dispersed suspensions showed high dispersion stability for long times. The study of the influence of dipolar molecules on the ER properties of the chitosan derivative dispersed suspensions under an electric field shows how to enhance the ER responses easily just by doping molecules.
    Soft Matter 05/2012; 8(23):6273-6279. · 4.15 Impact Factor
  • Young Gun Ko, Ung Su Choi
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    ABSTRACT: Potential applications for natural polymers have been intensively researched for a long time. Electrorheological (ER) fluids are a kind of colloidal suspension with rheological properties that can reversibly change over several orders of magnitude under a sufficiently strong electric field within a millisecond. By extension of the study on the properties of natural polymers to enlarge their applications, herein, we briefly review the ER materials based on natural polymers such as cellulose, starch, and chitosan. This highlight focuses on the current research of ER materials based on natural polymers and their perspective.
    Soft Matter 12/2011; 8(2):253-259. · 4.15 Impact Factor
  • Young Gun Ko, Ung Su Choi
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    ABSTRACT: Herein, the effect of pH on Cu(II) crystal growth onto the surface of chelating fiber is presented. Poly(acryloamidino ethyleneamine) and poly(acryloamidino diethylenediamine) are synthesized as chelating polymers, and Cu(OH)2 crystal growth with the change of pH in an aqueous solution are observed using field-emission scanning electron microscopy. It is shown that the shapes of grown Cu(II) crystals on the chelating polymers depend on their alkyl amine numbers. The best fits of the isotherm data for Cu2+ adsorption and Cu(OH)2 crystal growth on the chelating polymers are obtained by means of our developed model.
    Applied Physics Letters 08/2011; 99(9):094102-094102-3. · 3.79 Impact Factor
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    ABSTRACT: Herein, we demonstrate the adsorption process system with the diethylenetriamne coupled polyacrylonitrile fiber for the removal of Cu(II) and Cr(VI) ions in the aqueous solution. The synthesized chelating fiber showed a high adsorption capacity of 11.4 mequiv/g. Interestingly, the crystal growth of copper ions on the chelating fiber was observed during the adsorption process. The chelating fiber packed column showed the high performance of the removal of Cu(II) in the aqueous solution due to the distinct characteristic of the crystal growth of metal ions on the chelating fiber. After Cu(II) adsorption on the chelating fiber, the color of the fiber changed to light blue from yellow. The isotherm parameter n of 1.991 was obtained with Freundlich isotherm model for the adsorption equilibrium study which indicates that Cu(II) adsorption on the chelating fiber is very favorable due to n>1. The pseudo-first-order and pseudo-second-order model equations were used for the kinetic study.
    Journal of hazardous materials 08/2011; 194:92-9. · 4.14 Impact Factor
  • Young Gun Ko, Seung Su Shin, Ung Su Choi
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    ABSTRACT: CO(2) emissions, from fossil-fuel-burning power plants, the breathing, etc., influence the global worming on large scale and the man's work efficiency on small scale. The reversible capture of CO(2) is a prominent feature of CO(2) organic-inorganic hybrid adsorbent to sequester CO(2). Herein, (3-aminopropyl) trimethoxysilane (APTMS), [3-(methylamino)propyl] trimethoxysilane (MAPTMS), and [3-(diethylamino) propyl] trimethoxysilane (DEAPTMS) are immobilized on highly ordered mesoporous silicas (SBA-15) to catch CO(2) as primary, secondary, and tertiary aminosilica adsorbents. X-ray photoelectron spectroscopy was used to analyze the immobilized APTMS, MAPTMS, and DEAPTMS on the SBA-15. We report an interesting discovery that the CO(2) adsorption and desorption on the adsorbent depend on the amine type of the aminosilica adsorbent. The adsorbed CO(2) was easily desorbed from the adsorbent with the low energy consumption in the order of tertiary, secondary, and primary amino-adsorbents while the adsorption amount and the bonding-affinity increased in the reverse order. The effectiveness of amino-functionalized (1(o), 2(o), and 3(o) amines) SBA-15s as a CO(2) capturing agent was investigated in terms of adsorption capacity, adsorption-desorption kinetics, and thermodynamics. This work demonstrates apt amine types to catch CO(2) and regenerate the adsorbent, which may open new avenues to designing "CO(2) basket".
    Journal of Colloid and Interface Science 04/2011; 361(2):594-602. · 3.55 Impact Factor
  • Macromolecular Chemistry and Physics 04/2011; 212(14):1443 - 1450. · 2.39 Impact Factor
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    ABSTRACT: Herein, the effect of the degree of deacetylation (DD) on the gelation of the chitosan dispersed suspension as an electrorheological (ER) fluid under an electric field is presented. The fluids were prepared by dispersing the chitin and the chitosan particles having various DDs into silicone oil, and they were evaluated under various electric fields. The alignment of chitosan particles in the fluid was also observed using an optical microscope under the electric field. The formed fibrous structure between electrodes are though to continue to the viscosity increase, because an attempt to move one electrode relative to the order would be hindered by the drag of the dangling fibrils. A noteworthy result is that the region of the frequency for gel state of the ER fluids increased in the order of chitosan DD 99.3, 93.4, 73.2, 83.8, and 87.3% under electric fields while the modulus of the fluids increased in the reverse order. This order was well-matched with the result of dielectric constants and yield stresses of ER fluids. The study of influence of DD on the gelation of the chitosan dispersed suspension under an electric field shows the relevance of the chemical composition of the heteropolysaccharide (chitin-chitosan copolymer) to the rheological and electric properties of ER suspensions.
    ACS Applied Materials & Interfaces 03/2011; 3(4):1289-98. · 5.01 Impact Factor
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    ABSTRACT: Herein, we demonstrate the structure of the PS colloidal crystals which were fabricated on the hydrophilic/hydrophobic Si wafers by a spin-coating technique. Monodisperse PS colloids are spin-coated onto self-assembled monolayers of 3-(aminopropyl)triethoxysilane and propyltrimethoxysilane coated Si wafers. PS spheres organized as ordered close-packed face-centered cubic structure with (1 1 1) planes on the hydrophilic surface while they gathered without the crystal structure on the hydrophobic surface. This paper also reports a simple and rapid method to fabricate the close-packed structure of hollow TiO2 spheres. The colloidal crystal of TiO2 hollow spheres was prepared using the PS sphere template on the hydrophobic surface. The mechanism for the growing multilayers of self-assembled PS particles from a suspension onto a hydrophilic and hydrophobic Si wafer substrates using the spin-coating method at various rotating speeds is also discussed in this paper.Graphical abstractThe TiO2 inverse opals were fabricated using the PS opal templates which were prepared on the hydrophilic and the hydrophobic surfaces by the spin-coating method.Highlights► PS colloidal crystals were fabricated on the hydrophilic and the hydrophobic surfaces by spin-coating. ► The structure of the spin-coated PS colloidal crystals depended on the surface wettability. ► The mechanism for the growing multilayers of self-assembled spheres by the spin-coating method is discussed. ► This work demonstrates the rapid and simple method for the fabrication of colloidal crystal of TiO2 hollow spheres.
    Colloids and Surfaces A Physicochemical and Engineering Aspects 01/2011; 385:188-194. · 2.11 Impact Factor
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    ABSTRACT: The analysis on molecular interaction mechanism in the polymer electrolyte film should be preceded since high mobile ions in the film are required to fabricate the high ionic-conducting solid polymer electrolyte. We focused this study on analyzing the molecular interaction mechanism in the novel solid polymer electrolyte comprising cellulose phthalate (CP) and LiClO4. Li+ cation formed not only ionic-bond with carboxyl group but also the coordination with carbonyl and ether groups in CP at the low LiClO4 concentration, while it formed only the ionic-bond at the high concentration. This behavior also influenced the ionic conductivity of the CP/LiClO4 composite that the conductivity values increase rapidly due to the decrease of the coordinations as LiClO4 concentration increases, and then decrease due to the low ionic mobility at higher LiClO4.
    Solid State Ionics 08/2010; 181:1178-1182. · 2.05 Impact Factor
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    ABSTRACT: This paper focuses on the influence of metal ions on electrorheological and electric properties. The metal particle has not been used as an electrorheological suspension due to the high conductivity and the sedimentation in the suspension although it is expected good electrical properties. In this study, carboxyl group and metal ions were introduced to the surface of the chitosan particle to confirm the influence of the metal ion on the electrorheological property. Although the synthesized chitosan succinate showed good electrorheological property, its metal complex (chitosan succinate–metal complex formed with Al3+, Cu2+, Ni2+, Fe2+, or Zn2+) dispersed suspension showed the low electro-response property and high values of current density and conductivity.
    Colloids and Surfaces A Physicochemical and Engineering Aspects 01/2010; 371:76-80. · 2.11 Impact Factor
  • Young Gun Ko, Ung Su Choi, Yong Jin Chun
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    ABSTRACT: Different-sized particles dispersed electrorheological (ER) fluids were fabricated with poly(acryloamidino diethylenediamine) to observe the influence of the particle size on ER behaviors. The fine particles dispersed ER suspension showed stable shear stress under a DC electric field. On the other hand, the rough particles dispersed suspension showed trembling shear stress which is divided into four regions in a plot of shear stress against shear rate. Our suggested spring-damper model equation treated the wide range of shear rate and specific (trembling) behaviors of shear stress in ER fluids. In this study, we successfully obtained various ER fluids showing different behaviors just by changing the size of particles in the ER fluids. All of the curves of the shear stress plotted against shear rate were fitted well by our spring-damper model.
    Journal of Colloid and Interface Science 05/2009; 335(2):183-8. · 3.55 Impact Factor
  • Source
    Young Gun Ko, Ung Su Choi, Yong Jin Chun
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    ABSTRACT: An electro-rheological (ER) fluid showing trembling shear behavior was fabricated with chitosan particles that had benzene, amine and azo-pendent side groups. This modified-chitosan dispersed suspension showed four regions in a plot of shear stress against shear rate at high electric field. We analyzed this specific behavior with our suggested model. The model was developed with the spring-damper model. Our suggested model equation treated the wide range of shear rate and specific behaviors of shear stress in ER fluids. In this study, we successfully obtained various ER fluids showing different behaviors just by changing the side functional groups of the particles in the ER fluids. All of the curves of the shear stress plotted against shear rate were fitted well by our spring-damper model. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/58575/1/890_ftp.pdf
    Macromolecular Chemistry and Physics 01/2008; · 2.39 Impact Factor
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    ABSTRACT: A viscose rayon succinate (VRS) was synthesized using viscose rayon, succinic anhydride and DMSO. The VRS was well characterized by C13 nuclear magnetic resonance, Fourier transform infrared analysis and properties of the VRS up taking trivalent metals from aqueous solution were investigated. Both esterification and carboxyl bonding of the VRS were assigned essentially at 1729 and 1693 cm−1, respectively. And the essential band of bonding between metal and the material was determined at 1605–1639 cm−1. The available adsorption capacity, degree of substitution and pKa of the VRS were 6.2mequiv/g, 2.5 and 3.72, respectively. The adsorption of metal ions on the VRS follows the order of Cr3+>Al3+>Fe3+ with maximum adsorptions capacities 1.48, 1.059 and 1.029 mmol/g. An equilibrium modeling, which is obtained from chemical potential and Boltzmann distribution, was demonstrated trivalent metal adsorption on the VRS in different pHs. Surface potential, Ψ0, an effective ratio of surface equilibrium constants, Keffect, the probability factor P(A) and a degree of protonation, χ represent the physicochemical interactions between carboxyl group and metal ions.
    Polymer Journal 01/2008; 40(4):302-309. · 1.50 Impact Factor
  • Young Gun Ko, Bo Hyun Sung, Ung Su Choi
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    ABSTRACT: This paper focused on effects of amine and π-orbital for enhancing electrorheological properties. Various aminated chitosans were synthesized by coupling of diethylenetriamine, melamine, and Bismarck brown R onto chitosan in this study. After comparing the shear stress of all prepared ER fluids, melamine and Bismarck brown R coupled chitosans showed higher shear stress than other ER chitosan derivatives. Because amine group is cation, cation–π interaction could be expected for enhancing shear stress together with π–π stacking. And these aminated chitosans showed low current density and conductivity due to the cation–π interaction not to the π–π stacking.
    Colloids and Surfaces A-physicochemical and Engineering Aspects - COLLOID SURFACE A. 01/2007; 305(1):120-125.
  • Young Gun Ko, Ung Su Choi
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    ABSTRACT: In this study, polymeric chelating fiber with good adsorbing capacity (11.4mequiv./g) and activated carbon fiber with high specific area (1560m2/g) were synthesized to compare the adsorption of heavy metal ions on these materials. The adsorption isotherm of various cations on activated carbon fiber and poly(acrylo-amidino diethylenediamine) showed similar adsorption behavior. High adsorptions were found at high pHs. At low pHs, adsorbed H+s on the benzene (in the case of activated carbon fiber) and amine groups (in the case of poly(acrylo-amidino diethylenediamine)) blocked activated carbon fiber–metal complex and poly(acrylo-amidino diethylenediamine)–metal complex formations. Metal ion adsorption on activated carbon fiber was lower than that on poly(acrylo-amidino diethylenediamine) due to metal crystal growth on poly(acrylo-amidino diethylenediamine) although activated carbon fiber has high specific area. In the case of anions adsorption, much higher levels of adsorption were observed at lower pHs, but not at higher pHs due to H+s. In conclusion, the results suggest that metal crystal growth using functional group on the surface is more effective to remove metal ions in aqueous solution than high specific area.
    Separation and Purification Technology - SEP PURIF TECHNOL. 01/2007; 57(2):338-347.

Publication Stats

112 Citations
106.43 Total Impact Points

Institutions

  • 2000–2013
    • Korea Institute of Science and Technology
      • • Center for Urban Energy System Research
      • • Clean Energy Research Center
      Seoul, Seoul, South Korea
  • 2009
    • University of Michigan
      • Department of Biologic and Materials Sciences
      Ann Arbor, MI, United States
  • 2002
    • Sangmyung University
      • Department of Industrial Chemistry
      Seoul, Seoul, South Korea