Publications by authors named "Hoseok Park"

17 Publications

  • Page 1 of 1

Enhanced pseudocapacitance of ionic liquid/cobalt hydroxide nanohybrids.

ACS Nano 2013 Mar 18;7(3):2453-60. Epub 2013 Feb 18.

Division of Materials Science, Korea Basic Science Institute, Daejeon 305-333, Republic of Korea.

Development of nanostructured materials with enhanced redox reaction capabilities is important for achieving high energy and power densities in energy storage systems. Here, we demonstrate that the nanohybridization of ionic liquids (ILs, 1-butyl-3-methylimidazolium tetrafluoroborate) and cobalt hydroxide (Co(OH)2) through ionothermal synthesis leads to a rapid and reversible redox reaction. The as-synthesized IL-Co(OH)2 has a favorable, tailored morphology with a large surface area of 400.4 m(2)/g and a mesopore size of 4.8 nm. In particular, the IL-Co(OH)2-based electrode exhibits improvement in electrochemical characteristics compared with bare Co(OH)2, showing a high specific capacitance of 859 F/g at 1 A/g, high-rate capability (∼95% retention at 30 A/g), and excellent cycling performance (∼96% retention over 1000 cycles). AC impedance analysis demonstrates that the introduction of ILs on Co(OH)2 facilitates ion transport and charge transfer: IL-Co(OH)2 shows a higher ion diffusion coefficient (1.06 × 10(-11) cm(2)/s) and lower charge transfer resistance (1.53 Ω) than those of bare Co(OH)2 (2.55 × 10(-12) cm(2)/s and 2.59 Ω). Our density functional theory (DFT) calculations reveal that the IL molecules, consisting of anion and cation groups, enable easier hydrogen desorption/adsorption process, that is, a more favorable redox reaction on the Co(OH)2 surface.
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http://dx.doi.org/10.1021/nn305750sDOI Listing
March 2013

Charge transfer interactions between conjugated block copolymers and reduced graphene oxides.

Chem Commun (Camb) 2011 Oct 22;47(37):10293-5. Epub 2011 Aug 22.

Department of Chem. & Biomolecular Eng. (BK 21), KAIST, 335 Gwahagno, Yuseong-gu, Daejeon 305-701, Republic of Korea.

The charge transfer interactions between reduced graphene oxides and conjugated block copolymers were confirmed by various spectroscopic methods, giving rise to manipulation of the electrical properties of the former.
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http://dx.doi.org/10.1039/c1cc13465eDOI Listing
October 2011

Ultrafast and continuous synthesis of unaccommodating inorganic nanomaterials in droplet- and ionic liquid-assisted microfluidic system.

J Am Chem Soc 2011 Sep 23;133(37):14765-70. Epub 2011 Aug 23.

National Creative Research Center of Applied Microfluidic Chemistry, Chungnam National University, Daejeon 305-764, South Korea.

Despite many efforts on the synthesis of inorganic nanomaterials with uniform structure and narrow size distribution in a fast and continuous way, it is still a critical challenge in the chemistry research community due to the uncontrollable mass and heat transfer and the harsh experimental conditions of high temperature and pressure. Here we report a droplet- and ionic liquid-assisted microfluidic (DIM) synthesis method, which takes full advantage of both ionic liquids and droplet-assisted microreaction systems, for an ultrafast, mild, and continuous synthesis of various inorganic nanomaterials that takes only tens of minutes rather than days that are usually needed to synthesize. In particular, unaccommodating inorganic nanomaterials that are difficult to produce, such as nanoporous ZSM-5, γ-AlOOH, and β-FeOOH nanorods, were synthesized in only "20 minutes" of reaction time even with simple instrument. The DIM method delineated herein would offer a breakthrough synthetic approach for functional but unaccommodating inorganic nanomaterials in a continuous and mild manner.
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http://dx.doi.org/10.1021/ja2054429DOI Listing
September 2011

Facilitated ion transport in all-solid-state flexible supercapacitors.

ACS Nano 2011 Sep 10;5(9):7205-13. Epub 2011 Aug 10.

Department of Chemical & Biomolecular Engineering (BK21 program), KAIST, Daejeon 305-701, Republic of Korea.

The realization of highly flexible and all-solid-state energy-storage devices strongly depends on both the electrical properties and mechanical integrity of the constitutive materials and the controlled assembly of electrode and solid electrolyte. Herein we report the preparation of all-solid-state flexible supercapacitors (SCs) through the easy assembly of functionalized reduced graphene oxide (f-RGO) thin films (as electrode) and solvent-cast Nafion electrolyte membranes (as electrolyte and separator). In particular, the f-RGO-based SCs (f-RGO-SCs) showed a 2-fold higher specific capacitance (118.5 F/g at 1 A/g) and rate capability (90% retention at 30 A/g) compared to those of all-solid-state graphene SCs (62.3 F/g at 1A/g and 48% retention at 30 A/g). As proven by the 4-fold faster relaxation of the f-RGO-SCs than that of the RGO-SCs and more capacitive behavior of the former at the low-frequency region, these results were attributed to the facilitated ionic transport at the electrical double layer by means of the interfacial engineering of RGO by Nafion. Moreover, the superiority of all-solid-state flexible f-RGO-SCs was demonstrated by the good performance durability under the 1000 cycles of charging and discharging due to the mechanical integrity as a consequence of the interconnected networking structures. Therefore, this research provides new insight into the rational design and fabrication of all-solid-state flexible energy-storage devices as well as the fundamental understanding of ion and charge transport at the interface.
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http://dx.doi.org/10.1021/nn202020wDOI Listing
September 2011

Programmable peptide-directed two dimensional arrays of various nanoparticles on graphene sheets.

Nanoscale 2011 Aug 22;3(8):3208-13. Epub 2011 Jun 22.

Department of Chem. & Biomolecular Eng. (BK 21), KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon, 305-701, Republic of Korea.

In this research, we report an innovative, chemical strategy for the in situ synthesis and direct two-dimensional (2D) arraying of various nanoparticles (NPs) on graphenes using both programmed-peptides as directing agents and graphenes as pre-formed 2D templates. The peptides were designed for manipulating the enthalpic (coupled interactions) constraint of the global system. Along with the functionalization of graphene for the stable dispersion, peptides directed the growth and array of NPs in a controllable manner. In particular, the sequences of peptides were encoded by the combination of glutamic acid (E), glycine (G), and phenylalanine (F) amino acids as follows: (E-G-F)(3)-G, with E for the interaction with NPs and F and G for the interaction with graphenes. For the entropic (restricted geometry) constraint, graphene was used as a 2D scaffold to tune the size, density, and position of NPs, while maintaining the intrinsic properties for electrochemical applications. The excellent quality of the resultant hybrids was demonstrated by their high electrocatalytic activity in the electrooxidation of methanol. This synergistic combination of peptides and graphenes allowed for a uniform 2D array and spontaneous organization of various NPs (i.e., Pt, Au, Pd, and Ru), which would greatly expand the utility and versatility of this approach for the synthesis and array of the advanced nanomaterials.
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http://dx.doi.org/10.1039/c1nr10276aDOI Listing
August 2011

Innovative polymer nanocomposite electrolytes: nanoscale manipulation of ion channels by functionalized graphenes.

ACS Nano 2011 Jun 6;5(6):5167-74. Epub 2011 May 6.

Department of Chemical & Biomolecular Engineering (BK21 program), KAIST, Daejeon 305-701, Republic of Korea.

The chemistry and structure of ion channels within the polymer electrolytes are of prime importance for studying the transport properties of electrolytes as well as for developing high-performance electrochemical devices. Despite intensive efforts on the synthesis of polymer electrolytes, few studies have demonstrated enhanced target ion conduction while suppressing unfavorable ion or mass transport because the undesirable transport occurs through an identical pathway. Herein, we report an innovative, chemical strategy for the synthesis of polymer electrolytes whose ion-conducting channels are physically and chemically modulated by the ionic (not electronic) conductive, functionalized graphenes and for a fundamental understanding of ion and mass transport occurring in nanoscale ionic clusters. The functionalized graphenes controlled the state of water by means of nanoscale manipulation of the physical geometry and chemical functionality of ionic channels. Furthermore, the confinement of bound water within the reorganized nanochannels of composite membranes was confirmed by the enhanced proton conductivity at high temperature and the low activation energy for ionic conduction through a Grotthus-type mechanism. The selectively facilitated transport behavior of composite membranes such as high proton conductivity and low methanol crossover was attributed to the confined bound water, resulting in high-performance fuel cells.
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http://dx.doi.org/10.1021/nn2013113DOI Listing
June 2011

Ionic liquid-assisted direct synthesis of PdO nanoparticles immobilized on boehmite nanoparticles.

J Colloid Interface Sci 2011 May 1;357(1):46-9. Epub 2011 Feb 1.

Department of Chemical Engineering, College of Engineering, Kyung Hee University, 1 Seochon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-701, Republic of Korea.

We demonstrated a simple route to simultaneously synthesize PdO and boehmite nanoparticles, and to directly immobilize the former on the latter using an ionic liquid (IL)-assisted one-pot solution method. PdO nanoparticles were directly immobilized on boehmite nanoparticles, and their amount and distribution were controlled by the stoichiometry of the mixture. In particular, γ-alumina nanofibers, which were topochemically transformed from boehmites, exhibited lengths of ca. 40-70 nm and diameters of ca. 1.5-3 nm, while PdO nanoparticles had diameters of ca. 2-4 nm. The nanocrystalline structures of the PdO nanoparticles immobilized on the boehmite nanoparticles were characterized by high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), and (27)Al nuclear magnetic resonance (NMR). The one-step synthetic method described herein allows for the design and fabrication of host-guest systems of inorganic or metallic nanomaterials with hetero-nanostructures.
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http://dx.doi.org/10.1016/j.jcis.2011.01.084DOI Listing
May 2011

Interionic interactions of binary gels consisting of pyrrolidinium-based zwitterionic compounds and lithium salts.

J Phys Chem B 2011 Mar 3;115(8):1743-50. Epub 2011 Feb 3.

Department of Chemical Engineering, College of Engineering, Kyung Hee University, 1 Seochon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-701, Korea.

We demonstrated thermal transitions and physical gelation of binary ionic salts through interionic interactions, which consist of pyrrolidinium-N-propanesulfonate zwitterionic compound (PyrZIC) and lithium bis(trifluorosulfonyl)imide (LiTFSI). The transition behaviors of binary ionic gels were attributed to conformational changes in the cations and anions of PyrZIC and LiTFSI as analyzed by density functional theory (DFT), principal component analysis (PCA), and two-dimensional infrared correlation spectroscopy (2D IR COS). Furthermore, the geometries of binary PyrZIC-LiTFSI systems were strongly influenced by the electrostatic interactions between two ionic salts. The different dynamic processes in the PyrZIC- and LiTFSI-rich phases, which are classified by the transition point of PCA plots, were induced by the conformational changes in the respective interaction fields, as shown by 2D correlation spectra. In particular, LiTFSI-rich binary gels revealed characteristic four-leaf-clover and butterfly patterns under their unique chemical circumstances, which were different from those of PyrZIC-rich gels. Consequently, these computational and experimental investigations provide an analytical tool to understand the physical phenomenon and interactions occurring in the unveiled and complicated systems.
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http://dx.doi.org/10.1021/jp1062176DOI Listing
March 2011

Microwave-assisted synthesis of highly water-soluble graphene towards electrical DNA sensor.

Nanoscale 2010 Dec 25;2(12):2692-7. Epub 2010 Oct 25.

Department of Chemical & Biomolecular Engineering (BK21), KAIST, 335 Gwahangno, Yuseong-gu, Daejeon 305-701, Republic of Korea.

Graphene sheets have the potential for practical applications in electrochemical devices, but their development has been impeded by critical problems with aggregation of graphene sheets. Here, we demonstrated a facile and bottom-up approach for fabrication of DNA sensor device using water-soluble sulfonated reduced graphene oxide (SRGO) sheets via microwave-assisted sulfonation (MAS), showing enhanced sensitivity, reliability, and low detection limit. Key to achieving these performances is the fabrication of the SRGOs, where the MAS method enabled SRGOs to be highly dispersed in water (10 mg mL(-1)) due to the acidic sulfonated groups generated within 3 min of the functionalization reaction. The water-soluble SRGO-DNA (SRGOD) hybrids prepared by electrostatic interactions between a flat single layer of graphene sheets and DNAs are suitable for fabrication of electrical DNA sensor devices because of the unique electrical characteristics of SRGODs. The high sensing performance of SRGOD sensors was demonstrated with detection of DNA hybridization using complementary DNAs, single base mismatched DNAs, and noncomplementary DNAs, with results showing higher sensitivity and lower detection limit than those of reduced graphene oxide-based DNA sensors. Simple and easy fabrication of DNA sensor devices using SRGODs is expected to provide an effective way for electrical detection of DNA hybridization using miniature sensors without the labor-intensive labeling of the sensor and complex measurement equipment.
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http://dx.doi.org/10.1039/c0nr00562bDOI Listing
December 2010

Immobilization of genetically engineered fusion proteins on gold-decorated carbon nanotube hybrid films for the fabrication of biosensor platforms.

J Colloid Interface Sci 2010 Oct 30;350(2):453-8. Epub 2010 Jun 30.

Department of Chemical Engineering, Kyung Hee University, 1 Seocheon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-701, Republic of Korea.

We have demonstrated the fabrication of the biosensor platforms by means of the integration of the genetically engineered fusion proteins and the uniform gold nanoparticle-deposited multi-walled nanotube hybrid (Au-MWNT-HB) films for the detection of C-reactive protein (CRP). Au-MWNT-HB films were used as a good electrochemical transducer due to their excellent electrical properties and large surface areas for the signal transduction, while the genetically engineered fusion proteins, or 6His-GBP-SpA fusion proteins, specifically bind onto the surface of the Au-MWNT-HB films and efficiently immobilize bioreceptors for the detection of CRP. As-obtained biosensor platforms were characterized by electrochemical and optical analysis and revealed better performance compared to conventional Au-based biosensors. The concept delineated herein opens a new insight into nanobiotechnology through the integration of genetically engineered biomaterials with carbon nanotube (CNT)-based nanohybrids for emerging applications.
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http://dx.doi.org/10.1016/j.jcis.2010.06.058DOI Listing
October 2010

Solution chemistry of self-assembled graphene nanohybrids for high-performance flexible biosensors.

ACS Nano 2010 May;4(5):2910-8

Department of Chemical & Biomolecular Engineering, KAIST, Daejeon 305-701, Korea.

We report the preparation of free-standing flexible conductive reduced graphene oxide/Nafion (RGON) hybrid films by a solution chemistry that utilizes self-assembly and directional convective-assembly. The hydrophobic backbone of Nafion provided well-defined integrated structures, on micro- and macroscales, for the construction of hybrid materials through self-assembly, while the hydrophilic sulfonate groups enabled highly stable dispersibility ( approximately 0.5 mg/mL) and long-term stability (2 months) for graphene. The geometrically interlocked morphology of RGON produced a high degree of mechanical integrity in the hybrid films, while the interpenetrating network constructed favorable conduction pathways for charge transport. Importantly, the synergistic electrochemical characteristics of RGON were attributed to high conductivity (1176 S/m), facilitated electron transfer (ET), and low interfacial resistance. Consequently, RGON films obtained the excellent figure of merit as electrochemical biosensing platforms for organophosphate (OP) detection, that is, a sensitivity of 10.7 nA/microM, detection limit of 1.37 x 10(-7) M, and response time of <3 s. In addition, the reliability of RGON biosensors was confirmed by a fatigue test of 100 bending cycles. The strategy described here provides insight into the fabrication of graphene and hybrid nanomaterials from a material perspective, as well as the design of biosensor platforms for practical device applications.
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http://dx.doi.org/10.1021/nn100145xDOI Listing
May 2010

Spectroscopic and computational insight into the intermolecular interactions between Zwitter-type ionic liquids and water molecules.

Chemphyschem 2010 Jun;11(8):1711-7

Department of Chemical Engineering, College of Engineering, Kyung Hee University, 1 Seochong, Giheung, Yongin, Gyeonggi, 446-701, Republic of Korea.

Geometric and conformational changes of zwitter-type ionic liquids (ZILs) due to hydrogen-bonding interactions with water molecules are investigated by density functional theory (DFT), two-dimensional IR correlation spectroscopy (2D IR COS), and pulsed-gradient spin-echo NMR (PGSE NMR). Simulation results indicate that molecular structures in the optimized states are strongly influenced by hydrogen bonding of water molecules with the sulfonate group or imidazolium and pyrrolidinium rings of 3-(1-methyl-3-imidazolio)propanesulfonate (1) and 3-(1-methyl-1-pyrrolidinio)propanesulfonate (2), respectively. Concentration-dependent 2D IR COS reveals kinetic conformational changes of the two ZIL-H(2)O systems attributable to intermolecular interactions, as well as the interactions of sulfonate groups and imidazolium or pyrrolidinium rings with water molecules. The dramatic changes in the (1)H self-diffusion coefficients elucidate the formation of proton-conduction pathways consisting of ZIL networks. In ZIL domains, protons are transferred by a Grotthuss-type mechanism through formation, breaking, and restructuring of bonds between ZILs and H(2)O, leading to an energetically favorable state. The simulation and experimental investigations delineated herein provide a perspective to understanding the interactions with water from an academic point of view as well as to designing ILs with desired properties from the viewpoint of applications.
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http://dx.doi.org/10.1002/cphc.200900925DOI Listing
June 2010

Energy transfer in ionic-liquid-functionalized inorganic nanorods for highly efficient photocatalytic applications.

Small 2010 Jan;6(2):290-5

Department of Chem. & Biomolecular Eng. (BK 21), KAIST, Daejeon, Republic of Korea.

Energy transfer in self-assembled ionic liquids (ILs) and iron oxyhydroxide nanocrystals and the controlled surface chemistry of functionalized nanomaterials for photocatalytic applications are reported. Self-assembled ILs play the role of multifunctional materials in terms of constructing a well-designed nanostructure, controlling the surface chemistry, and triggering the energy transfer of functionalized materials. IL-functionalized beta-FeOOH nanorods show approximately 10-fold higher performances than those of commercial materials due to the synergistic effect of well-defined nanomaterials in diffusion-controlled reactions, specific interactions with target pollutants, and energy transfers in hybrid materials. In particular, the energy transfer in C(4)MimCl-functionalized beta-FeOOH nanorods enhances photocatalytic activity due to the generation of Fe(2+). The strategy described herein provides new insight into the rational design of functionalized inorganic nanomaterials for applications in emerging technologies.
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http://dx.doi.org/10.1002/smll.200901592DOI Listing
January 2010

Tracking the transition behavior and dynamics of ionic transport in crystalline ionic gel electrolytes.

Chem Commun (Camb) 2009 Nov 24(42):6388-90. Epub 2009 Sep 24.

Department of Biological Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA.

The transition behavior and dynamics of ionic transport were strongly influenced by changes in the crystal structure and interaction field of the crystalline ionic gel electrolytes with respect to chemical compositions, as proven by impedance, (7)Li NMR, PCA and 2D IR COS.
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http://dx.doi.org/10.1039/b910600fDOI Listing
November 2009

Green one-pot assembly of iron-based nanomaterials for the rational design of structure.

Chem Commun (Camb) 2009 Jul 29(27):4058-60. Epub 2009 May 29.

Department of Chemistry & Biomolecular Engineering (BK 21), KAIST, 335 Gwahagno, Yuseong-gu, Daejeon 305-701, Republic of Korea.

Green one-pot solution chemistry described herein could delicately manipulate the size and shape of iron oxyhydroxide nanocrystals, even in the aqueous phase, and easily derive a family of iron-based nanomaterials.
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http://dx.doi.org/10.1039/b906464hDOI Listing
July 2009

Analysis of the CO2 and NH3 reaction in an aqueous solution by 2D IR COS: formation of bicarbonate and carbamate.

J Phys Chem A 2008 Jul 27;112(29):6558-62. Epub 2008 Jun 27.

Department of Chemical and Biomolecular Engineering, BK21 Program, KAIST, Yusong-gu, Daejeon, Republic of Korea.

The two-dimensional (2D) infrared correlation spectra obtained from the reaction time- and concentration-dependent IR spectra elucidates the reaction of CO2 and NH3 in an aqueous solution for CO2 absorption. In the synchronous 2D correlation spectra, the interrelation of the proton with carbamate and bicarbonate indicates that the pH level affected the formation reactions of the two products. Furthermore, the interrelation of carbamate with bicarbonate confirmed the conversion of carbamate into bicarbonate with the release of protons (or the decrease of the pH). From the experimental results including the asynchronous 2D correlation spectra, the reaction of the CO2 and aqueous ammonia proceeded through the following steps: formation of carbamate, formation of bicarbonate, release of protons, and conversion of carbamate into bicarbonate. The analysis of the formation of carbamate and bicarbonate by 2D infrared correlation spectroscopy provides useful information on the reaction mechanism of CO2 and NH3 in aqueous solutions.
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http://dx.doi.org/10.1021/jp800991dDOI Listing
July 2008

Influence of additives including amine and hydroxyl groups on aqueous ammonia absorbent for CO2 capture.

J Phys Chem B 2008 Apr 19;112(14):4323-8. Epub 2008 Mar 19.

Department of Chemical and Biomolecular Engineering (BK21 Program), KAIST, 373-1 Guseong-dong, Yuseong-gu, Daejeon, Republic of Korea.

Aqueous ammonia absorbent (10 wt %) was modified with four kinds of additives (1 wt %) including amine and hydroxyl groups, i.e., 2-amino-2-methyl-1-propanol (AMP), 2-amino-2-methyl-1,3-propandiol (AMPD), 2-amino-2-ethyl-1,3-propandiol (AEPD), and tri(hydroxymethyl) aminomethane (THAM), for CO(2) capture. The loss of ammonia by vaporization was reduced by additives, whereas the removal efficiency of CO(2) was slightly improved. These results were attributed to the interactions between ammonia and additives or absorbents and CO(2) via hydrogen bonding, as verified by FT-IR spectra and computational calculation. Molecular structures as well as binding energies were obtained from the geometries of (ammonia + additives) and (ammonia + additives + CO(2)) at the optimized state. These experimental and theoretical findings demonstrate that additives including amine and hydroxyl group are suitable for modifying aqueous ammonia absorbent for CO(2) removal.
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http://dx.doi.org/10.1021/jp711113qDOI Listing
April 2008
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