• Advances in nano research
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• v.1 no.2
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• pp.71-82
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• 2013

A simple chemical precipitation technique is reported for the synthesis of a hybrid nanostructure of single-wall carbon nanotubes (SWCNT) and titania ($TiO_2$) nanocrystals of average size 5 nm, which may be useful as a prominent photocatalytic material with improved functionality. The synthesized hybrid structure has been characterized by transmission electron microscopy (HRTEM), energy-dispersive X-ray analysis (EDAX), powder X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. It is clearly revealed that nearly monodispersed titania nanocrystals (anatase phase) of average size 5 nm decorate the surfaces of SWCNT bundles. The UV-vis absorption study shows a blue shift of 16 nm in the absorbance peak position of the composite material compared to the unmodified SWCNTs. The photoluminescence study shows a violet-blue emission in the range of 325-500 nm with a peak emission at 400 nm. The low temperature electrical transport property of the synthesized nanomaterial has been studied between 77-300 K. The DC conductivity shows semiconductor-like characteristics with conductivity increasing sharply with temperature in the range of 175-300 K. Such nanocomposites may find wide applications as improved photocatalyst due to transfer of photo-ejected electrons from $TiO_2$ to SWCNT, thus reducing recombination, with the SWCNT scaffold providing a firm and better positioning of the catalytic material.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.12
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• pp.878-881
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• 2013

In this study, we have fabricated the dye sensitized solar cell (DSSC) composed by a transparent conductive oxide (TCO), a nanocrystalline semiconductor film usually $TiO_2$, a sensitizer adsorbed on the surface of the semiconductor, an electrolyte containing a redox mediator and a counter electrode. The $TiO_2$ nanopowder was prepared by sol-gel methode. The HCl (hydrochloric acid) and TBAOH (Tetrabutyl amonium hydroxide) was added for improving the catalyst and distributed properties of $TiO_2$ nanopowder. Ammonium hydroixde was added in order to control the morphology and size of $TiO_2$ nano crystal. A $TiO_2$ paste for working electrode was prepared with the addition of HPC (hydroxypropyl cellulos) used as a binder of which volume was controled as 1.3, 1.5, 1.7, and 2.0%. The measured I-V curves of assembled DSSC showed that the cell with 1.7% HPC binder had the best efficiency of 6.79%.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.382-382
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• 2012

Nanostructures have a larger surface/volume ratio as well as unique mechanical, physical, chemical properties compared to existing bulk materials. Materials for biomedical implants require a good biocompatibility to provide a rapid recovery following surgical procedure and a stabilization of the region where the implants have been inserted. The biocompatibility is evaluated by the degree of the interaction between the implant materials and the cells around the implants. Recent researches on this topic focus on utilizing the characteristics of the nanostructures to improve the biocompatibility. Several studies suggest that the degree of the interaction is varied by the relative size of the nanostructures and cells, and the morphology of the surface of the implant [1, 2]. In this paper, we fabricate the nanowires on the Ti substrate for better biocompatible implants and other biomedical applications such as artificial internal organ, tissue engineered biomaterials, or implantable nano-medical devices. Nanowires are fabricated with two methods: first, nanowire arrays are patterned on the surface using e-beam lithography. Then, the nanowires are further defined with deep reactive ion etching (RIE). The other method is self-assembly based on vapor-liquid-solid (VLS) mechanism using Sn as metal-catalyst. Sn nanoparticle solutions are used in various concentrations to fabricate the nanowires with different pitches. Fabricated nanowries are characterized using scanning electron microscopy (SEM), x-ray diffraction (XRD), and high resolution transmission electron microscopy (TEM). Tthe biocompatibility of the nanowires will further be investigated.

• Journal of the Korean Chemical Society
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• v.60 no.5
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• pp.317-320
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• 2016

Efficient copper removal from water was achieved by using surface modified silica spheres with 3-mercaptopropyltrimethoxysilane (MPTMS) using base catalyst. The surface modification of silica spheres was performed by hydrolysis and condensation reactions of the MPTMS. The characteristic infrared absorption peaks at 2929, 1454, and 1343 cm⁻¹ represent the −CH₂ stretching vibration, asymmetric deformation, and deformation, respectively. The absorption peaks at 2580 and 693 cm⁻¹ corresponding the −SH stretching vibration and the C-S stretching vibration indicate the incorporation of MPTMS to the surface of silica spheres. Field emission scanning electron microscope (FESEM) image of the surface modified silica sphere (SMSS) shows nano-particles of MPTMS on the surface of silica spheres. High concentration of copper solution (1000 ppm) was used to test the copper removal efficiency and uptake capacity. The FESEM image of SMSS treated with the copper solution shows large number of copper lumps on the surface of SMSS. The copper concentration drastically decreased with increasing the amount of SMSS. The residual copper concentrations were analyzed using inductively coupled plasma mass spectrometer. The copper removal efficiency and uptake capacity with 1000 ppm of copper solution were 99.99 % and 125 mg/g, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.267.2-267.2
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• 2016

Semiconductor photo-catalysis offers the potential for complete removal of toxic chemicals through its effective and broad potential applications. Various new compounds and materials for chemical catalysts were synthesized in the past few decades. As one of the most important II-VI group semiconductors, zinc sulfide (ZnS) with a wide direct band gap of 3.8 eV has been extensively investigated and used as a catalyst in photochemistry, environmental protection and in optoelectronic devices. In this work, the ZnS films and nanostructures have been successfully prepared by wet chemical method. We show that the agglomerates with four successive scales are always observed in the case of the homogeneous precipitation of zinc sulfide. Hydrodynamics plays a crucial role to determine the size of the largest agglomerates; however, other factors should be invoked to interpret the complete structure. In addition, studies of the photocatalytic properties by exposure to UV light irradiation demonstrated that ZnS nanocrystals (NCs) are good photo-catalysts as a result of the rapid generation of electron-hole pairs by photo-excitation and the highly negative reduction potentials of excited electrons. A combination of their unique features of high surface-to volume ratios, carrier dynamics and rich photo-catalytic suggests that these ZnS NCs will find many interesting applications in semiconductor photo-catalysis, solar cells, environmental remediation, and nano-devices.

• Bulletin of the Korean Chemical Society
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• v.27 no.5
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• pp.759-761
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• 2006

The compound B(C6F5)3 and its variations have been widely employed as alkyl carbanion abstracting reagents to produce metallocene cations for olefin polymerization.1-3 Weakly coordinating anions containing boron can greatly improve the activity of metallocene catalysts used in industrial olefin polymerization4 and thus group IV and V metallocene complexes of the organohydroborate anions have been intensively investigated.5 Recently, many organohydroborate metallocene complexes have been reported by Shore and co-workers.6-8 A common structural feature of those complexes is the three-center two electron M-H-B bond, like that observed in transition metal tetrahydroborate complexes but the reactivity and fluxional behavior of organohydroborate complexes are unlike those of the tetrahydroborate analogues.6 Although many of those metallocenes have been synthesized, few complexes could be used in the olefin polymerization and then this laboratory has been involved in the chemistry of the cyclic organohydroborate anions, and their group IV metallocene derivatives for the catalyst.9 Described here is recent work that led to the preparation of a novel cyclic organohydroborate hafnocene complex (h5-C5H5)2Hf ？(μ-H)2BC8H14 ,Cl. The hafnocene complex contains the three-center two electron bond Hf-H-B10 in which the hydride abstraction for olefin polymerization may occur.

• Journal of the Korean Vacuum Society
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• v.12 no.1
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• pp.70-77
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• 2003

It is well Down that the growth of carbon nanotubes (CNTs) by chemical vapor deposition (CVD) using a transition metal catalyst is greatly enhanced in a nitrogen environment. We show here that the enhanced growth is closely related to the activated nitrogen and it's incorporation into the CNT wall and cap during growth. This behavior is consistent with theoretical calculations of CNx thin films, showing that nitrogen incorporation to the graphitic basal plane reduces the elastic strain energy for curving the graphitic layer. Enhanced CNT growth by nitrogen incorporation is thus due to a decrease in the activation energies required for nucleation and growth of the tubular graphitic layer.

• Carbon letters
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• v.12 no.4
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• pp.185-193
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• 2011

Carbon nanotubes (CNTs) have developed into one of the most competitively researched nano-materials of this decade because of their structural uniqueness and excellent physical properties such as nanoscale one dimensionality, high aspect ratio, high mechanical strength, thermal conductivity and excellent electrical conductivity. Mass production and structure control of CNTs are key factors for a feasible CNT industry. Water and ethanol vapor enhance the catalytic activity for massive growth of vertically aligned CNTs. A shower system for gas flow improves the growth of vertically aligned single walled CNTs (SWCNTs) by controlling the gas flow direction. Delivery of gases from the top of the nanotubes enables direct and precise supply of carbon source and water vapor to the catalysts. High quality vertically aligned SWCNTs synthesized using plasma enhance the chemical vapor deposition technique on substrate with suitable metal catalyst particles. This review provides an introduction to the concept of the growth of vertically aligned SWCNTs and covers advanced topics on the controlled synthesis of vertically aligned SWCNTs.

• Membrane and Water Treatment
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• v.1 no.3
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• pp.193-206
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• 2010

Organic fouling and biofouling pose a significant challenge to the membrane filtration process. Photocatalysis-membrane hybrid system is a novel idea for reducing these membranes fouling however, when $TiO_2 photocatalyst nanoparticles are used in suspension, catalyst recovery is not only imposes an extra step on the process but also significantly contributes to increased membrane resistance and reduced permeate flux. In this study, $TiO_2$ photocatalyst has been immobilized by coating on the microfiltration (MF) membrane surface to minimize organic and microbial fouling. Nano-sized $TiO_2$ was first synthesized by a sol-gel method. The synthesized $TiO_2$ was coated on a Poly Vinyl Difluoride (PVDF) membrane (MF) surface using spray coating and dip coating techniques to obtain hybrid functional composite membrane. The characteristics of the synthesized photocatalyst and a functional composite membrane were studied using numerous instruments in terms of physical, chemical and electrical properties. In comparison to the clean PVDF membrane, the $TiO_2$ coated MF membrane was found more effective in removing methylene blue (20%) and E-coli (99%).

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1220-1221
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• 2008

Submicron-sized conical-type tungsten(W) field-emitters based on carbon nanotubes(CNTs) are fabricated with the configuration of CNTs/catalyst(Ni)/buffer(Al/Ni/TiN)/W-tip. This study focuses on elucidating how the Al/Ni/TiN stacked buffer layer affects the structural properties of CNTs and the electron-emission characteristics of CNT-emitters. Field-emission scanning electron microscopy(FESEM), high-resolution transmission electron microscopy(HRTEM), and x-ray photoelectron spectroscopy(XPS) are used to monitor the nanostructures, surface morphologies, chemical bonds of all the catalysts and CNTs grown. The crystalline structure of CNTs is also characterized by Raman spectroscopy. Furthermore, the measurement of field-emission characteristics for the field-emitters fabricated shows that the emitter using the Al/Ni/TiN stacked buffer reveals the excellent performances.