Seung-Min Paek

Enhanced Cyclic Performance and Lithium Storage Capacity of SnO2/Graphene Nanoporous Electrodes with Three-Dimensionally Delaminated Flexible Structure

To fabricate nanoporous electrode materials with delaminated structure, the graphene nanosheets (GNS) in the ethylene glycol solution were reassembled in the presence of rutile SnO(2) nanoparticles. According to the TEM analysis, the graphene nanosheets are homogeneously distributed between the loosely packed SnO(2) nanoparticles in such a way that the nanoporous structure with a large amount of void spaces could be prepared. The obtained SnO(2)/GNS exhibits a reversible capacity of 810 mAh/g; furthermore, its cycling performance is drastically enhanced in comparison with that of the bare SnO(2) nanoparticle. After 30 cycles, the charge capacity of SnO(2)/GNS still remained 570 mAh/g, that is, about 70% retention of the reversible capacity, while the specific capacity of the bare SnO(2) nanoparticle on the first charge was 550 mAh/g, dropping rapidly to 60 mAh/g only after 15 cycles. The dimensional confinement of tin oxide nanoparticles by the surrounding GNS limits the volume expansion upon lithium insertion, and the developed pores between SnO(2) and GNS could be used as buffered spaces during charge/discharge, resulting in the superior cyclic performances.

Layer‐by‐Layer Films of Graphene and Ionic Liquids for Highly Selective Gas Sensing

The best of both worlds: Graphene/ionic liquid (G–IL) layered films were obtained by direct reduction of graphene oxide in the presence of ionic liquids, followed by reassembly through electrostatic layer-by-layer (LbL) adsorption (see picture). The layer spacing of the graphene sheets is regularly expanded upon insertion of ionic liquid molecules (green discs). Selective sensing of aromatic compounds (red spheres) by using the G–IL LbL films was also achieved.

Pre-swelled nanostructured electrode for lithium ion battery: TiO2-pillared layered MnO2

Porous structure of layered manganate pillared with titania nanoparticles has been realized by the exfoliation and reassembling route. First, the layered protonic manganese oxide, H0.13MnO2·0.7H2O, is exfoliated by the intercalation of tetrabutylammonium (TBA) ions, and then the exfoliated manganate nanosheets are reassembled in the presence of titania nanoparticles, which results in porous nanohybrid materials. X-Ray diffraction (XRD), cross-sectional transmission electron microscopy (TEM), and Mn K-edge X-ray absorption spectroscopy (XAS) analyses clearly show that the titania nanoparticles with a diameter of 1 nm are successfully intercalated into the two dimensional manganate lattice without any deterioration of electronic structure and local symmetry of Mn ion. According to the N2 adsorption–desorption isotherms, the present nanohybrid is determined to be highly porous with a high specific surface area (106 m2 g−1), which is 10 times larger than that (11 m2 g−1) of the pristine. Finally, electrochemical experiments demonstrate that the specific capacity of the present pillared material is 288 mA h g−1, which is significantly larger than the theoretical value (193 mA h g−1) from the physical mixture of the pristine potassium birnessite and titania nanoparticles.

Intercalative route to heterostructured nanohybrids

Abstract We have successfully synthesized inorganic–inorganic, organic–inorganic and bio-inorganic nanohybrids by applying an intercalation technique systematically to layered titanate, molybdenum disulfide (MoS 2 ), Bi-based cuprate superconductors (Bi 2 Sr 2 Ca m −1 Cu m O y ( m =1, 2, and 3; BSCCO)), and to layered double hydroxides (LDHs), those which are of high importance in terms of basic understanding of intercalation reactions and of their practical applications. The inorganic–inorganic systems such as TiO 2 -pillared titanate, TiO 2 -pillared MoS 2 , and CdS–MoS 2 hybrids were synthesized by exfoliation–restacking method. A novel pillaring process using an osmotic swelling was developed to prepare TiO 2 -pillared layered titanate with a large surface area, high thermal stability, and enhanced photocatalytic activity. And the intercalation of TiO 2 and/or CdS nanocluster into the two dimensional MoS 2 lattice could be also realized by exfoliating and reassembling the lithiated molybdenum disulfide (LiMoS 2 ) in the presence of cationic TiO 2 and/or CdS nanocluster in an aqueous solution, respectively, to obtain the semiconductor–semiconductor hybrids. On the other hands, the organic–inorganic hybrids were achieved via intercalative complexation of iodine intercalated BSCOO with organic salt of Py–C n H 2 n +1 I (Py=pyridine). The high- T c superconducting intercalate with its remarkable lattice expansion can be applied as a precursor for superconducting colloids when dispersed in an appropriate solvent. This superconducting hybrid material had an unique structural feature of a superconducting-insulating-superconducting multilayer with atomically clean interfaces. Especially, this organic–inorganic nanohybrid is expected to be a promising precursor for preparing the superconducting colloidal suspension, which could be applied to the fabrication of superconducting films or wires. Recently, we were very successful in demonstrating in which the formation of bio-inorganic hybrids stabilized in the interlayer space of LDH retain their chemical and biological integrity. If necessary, LDH, as a reservoir, can be intentionally removed by dissolving it in an acidic media in such a way the interlayer biomolecules can be recovered or the intercalated biomolecules can be released from the LDH via ion-exchange reaction in electrolyte. It is, therefore, concluded that the inorganic LDH can play a role as a gene reservoir or carrier for various unstable organic or bio-molecules such as drugs and genes.

Isolation and characterization of outer root sheath melanocytes of human hair follicles

Background  Outer root sheath melanocytes (ORSM) are not yet routinely cultured and their biology is not known in detail because of their relatively low numbers in the hair follicle and their limited proliferative capacity in in vitro culture in routine media.

A lattice-engineering route to heterostructured functional nanohybrids.

The fabrication of layered nanomaterials, such as inorganic-inorganic, organic-inorganic, and bioinorganic nanohybrids has been demonstrated through controlled lattice engineering techniques including intercalation, exfoliation-reassembling, and pillaring reactions. Such a lattice engineering method gives rise to an almost unlimited set of new hybrid compounds with a large spectrum of desirable properties. Due to the unique two-dimensional structures and properties, various kinds of functional nanohybrid materials can be utilized as photocatalysts, electrode materials, superconducting thin films, gas separation membranes, drug-delivery systems, and biomolecule reservoirs.

Colloidal behaviors of ZnO nanoparticles in various aqueous media

We have evaluated the particle sizes, zeta potentials and hydrodynamic radii of zinc oxide (ZnO) nanoparticles in various aqueous conditions such as deionized water, phosphate buffered saline and Minimum Essential Media Eagle. In order to study the size and surface chemistry effect in colloidal behaviors, different size of 20 and 70 nm ZnO nanoparticles were selected and their surface was modified with either citrate or L-serine. It was revealed that surface modification did not strongly affect the particle size or morphology but altered the surface charge and chemistry. In various aqueous media, although the surface charge of ZnO nanoparticles are slightly affected by the existence of electrolyte, the overall particle sizes and morphologies are determined to be preserved, suggesting that their properties as nanoparticles are not significantly changed in physiological conditions.

Rapid microwave-assisted synthesis of hybrid zeolitic–imidazolate frameworks with mixed metals and mixed linkers

Herein we report a new microwave-assisted synthetic strategy to rapidly prepare hybrid zeolitic–imidazolate frameworks (ZIFs): ZIFs with mixed metal centers and/or mixed linkers. The microwave-based method significantly shortens synthesis time, produces a higher yield, substantially reduces the amounts of ligands, and eliminates the use of deprotonating agents. The X-ray diffraction pattern reveals that mixed metal CoZn–ZIF-8 (i.e., ZIF-8 with both Co and Zn centers) maintains the sodalite (SOD) zeolitic topology from the ZIF-8 parent. Elemental mapping using energy-dispersive X-ray spectroscopy (EDS) and electronic/geometric information obtained from X-ray absorption spectroscopy (XAS) confirm the uniform distribution of tetrahedral Co and Zn metal centers within the same framework of the mixed-metal ZIF. The metal to nitrogen (M–N) stretching frequencies of IR bands were observed to be systematically blue-shifted as the Co/Zn ratio in the mixed metal ZIF increases. Furthermore, for the first time, a hybrid ZIF with both mixed metal centers (Co and Zn) and mixed linkers (2-methylimidazolate and benzimidazolate) was prepared through one-step microwave synthesis. Finally, mixed metal CoZn–ZIF-8 with a Co/Zn ratio of ∼1 was grown as membranes on porous α-Al2O3 supports, showing a higher propylene/propane separation factor (∼120) when compared to pure Zn–ZIF-8 membranes (∼63) prepared by a similar method.

TiO2-pillared clays with well-ordered porous structure and excellent photocatalytic activity

TiO2-pillared clays with well-ordered porous structures are successfully prepared via incorporating TiO2 nanosol particles into the clays, where empty octahedral sites are partially modified with divalent metal ions such as Mg2+ and Fe2+. The prepared TiO2-pillared mica exhibits excellent photocatalytic activity, which can be controlled by tuning the optical transparency of clay support rather than the specific surface area of the hybrid catalysts.

A Dual-Polymer Electrochromic Device with High Coloration Efficiency and Fast Response Time: Poly(3,4-(1,4-butylene-(2-ene)dioxy)thiophene)–Polyaniline ECD

A new dual-polymer electrochromic device (ECD) composed of poly(3,4-(1,4-butylene-(2-ene)dioxy)thiophene) (PBueDOT) and polyaniline (PANI) with a hydrophobic molten salt electrolyte has been developed. To build this system, an alkylenedioxy ring in the BueDOT backbone was expanded to include a strongly electron-donating alkylenedioxy bridge, and the thickness and surface morphology of the corresponding PBueDOT film were controlled systematically. Not only the dual-electrochromic-polymer-electrode system, but also the expanded alkylenedioxy ring in the BueDOT backbone, synergistically improved the electrochromic performance. From the coloration efficiency (CE) value calculations, we found that the CE was enhanced up to 930 cm(2) C(-1). Furthermore, these ECDs showed an extremely fast response time of less than 80 ms.