• 한국분말재료학회지
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• 제18권6호
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• pp.532-537
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• 2011

Thermally stable $TiO_2$/Pt/$SiO_2$ core-shell nanocatalyst has been synthesized by chemical processes. Citrated capped Pt nanoparticles were deposited on amine functionalized silica produced by Stober process. Ultrathin layer of titania was coated on Pt/$SiO_2$ for preventing sintering of the metal nanoparticles at high temperatures. Thermal stability of the metal-oxide hybrid catalyst was demonstrated heating the sample up to $600^{\circ}C$ in air and by investigating the morphology and integrity of the structure by transmission electron spectroscopy. The surface analysis of the constituent elements was performed by X-ray photoemission spectroscopy. The catalytic activity of the hybrid catalysts was investigated by CO oxidation reaction with oxygen as a model reaction.

• 한국의류학회지
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• 제37권2호
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• pp.224-234
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• 2013

This study investigates the fabrication of core-sheath nanocomposite fibers by locating germanium (Ge) and silicon dioxide ($SiO_2$) nanoparticles selectively in the sheath layer by co-axial electrospinning. Co-axially spun fibers were prepared by electrospinning a pure PVA solution and Ge/$SiO_2$/PVA solution as the core and sheath layer, respectively. Core-sheath nanocomposite fibers were electrospun under a variety of conditions that include various feed rates for the core and sheath solutions, voltages, and concentric needle diameters, in order to find an optimum spinning condition. Ge/$SiO_2$ nanocomposite fibers were also prepared by uniaxial electrospinning to compare fiber morphology and nanoparticle distribution with core-sheath nanofibers. Using scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray analysis, it was demonstrated that the co-axial approach resulted in the presence of nanoparticles near the surface region of the fibers compared to the overall distribution obtained for uni-axial fibers. The co-axially electrospun Ge/$SiO_2$/PVA nanofiber webs have possible uses in high efficiency functional textiles in which the nanoparticles located in the sheath region provide enhanced functionality.

• Journal of Magnetics
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• 제20권3호
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• pp.211-214
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• 2015

$Cr_2O_3$ nanoparticles were prepared via one-step reactive laser ablation of Cr in oxygen. The metastable $CrO_2$ phase was obtained through the subsequent oxidation of $Cr_2O_3$ nanoparticles under $O_2$ with gas pressures of up to 40 MPa. The as-prepared $Cr_2O_3$ nanoparticles are spherical or rectangular in shape with sizes ranging from 20 nm to 50 nm. High oxygen pressure annealing is effective in producing meta-stable $CrO_2$ from as-dried $Cr_2O_3$ nanoparticles, and the $Cr_2O_3$ nanoparticles exhibit a weak ferromagnetic behavior with an exchange bias of up to 11 mT that can be ascribed to the interfacial exchange coupling between uncompensated surface spins and the antiferromagnetic core. The $Cr_2O_3/CrO_2$ nanoparticles exhibit an enhanced saturation magnetization and a reduced exchange bias with an increasing faction of $CrO_2$ due to the elimination of uncompensated surface spins over the $Cr_2O_3$ nanoparticles when exposed to a high pressure of $O_2$ and/or possible phase segregation that results in a smaller grain size for both $Cr_2O_3$ and $CrO_2$.

• 한국광물학회지
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• 제21권3호
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• pp.321-329
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• 2008

비정질 규산염 나노입자는 지각에 풍부한 규소와 산소로 이루어진 비다공성 나노입자로서 광물학을 포함한 지구환경과학과 산업적 측면에서 모두 중요한 물질이다. 본 연구에서는 $^{1}H$과 $^{29}Si$ MAS NMR분광분석을 통해 7 nm와 14 nm 규산염 나노입자의 규소와 수소 원자 환경을 측정하고, 입자 크기에 따른 규산염 나노입자 원자 환경 변화를 규명하였다. NMR 스펙트럼의 화학적 이동 값의 이론적 배경을 이해하기 위해 양자화학계간을 통해 $Si_{3}O_{6}H_6,\;Si_{4}O_{5}H_{10},\;Si_{5}O_{4}H_{12}$ 분자계간모델의 화학 차폐를 계산하였다. $^{29}Si$ MAS NMR의 결과, 이중 실라놀(geminal silanol)과 단일 실라놀(single silanol), 실록산(siloxane) 구조의 Si 원자 환경에 해당하는 $Q^2,\;Q^3,\;O^4$가 구분되어 나타나며 입자 크기에 따라 $Q^2,\;Q^3,\;O^4$가 7 nm규산염 나노입자에는 $7{\pm}1%,\;27{\pm}2%,\;66{\pm}2%$, 14 nm 규산염 나노입자에는 $6{\pm}1%,\;21{\pm}2%,\;73{\pm}2%$의 분포를 갖는다. $Q^2,\;Q^3$ 구조는 나노 입자의 표면적에 대부분 존재하는 것으로 예상되었으나, 두 규산염 나노입자의 표면적 차이에 비해 $Q^2,\;Q^3$ 양의 차이가 적으며, 이는 입자 표면 뿐 아니라 입자 내부에도 $Q^2,\;Q^3$ 구조가 존재함을 의미한다. $^{1}H$ MAS NMR 스펙트럼은 물리흡착 된 물(physisorbed water), 수소결합 된 수산기(hydrogen bended silanol), 비 수소결합 된 수산기(non-hydrogen bonded silanol)를 구분하여 나타낸다. 14 nm 비정질 규산염 나노입자에 비해 7nm 나노입자에 약 3.4 배의 수소 원자가 존재하며, 더 강한 수소결합 세기를 갖는다. 전체 수산기 중에서 비 수소결합 된 수산기가 차지하는 비율이 7 nm 규산염 나노입자 보다 14 nm 규산염 나노입자에서 더 높으며, 이는 수소 원자간의 상대적 거리(proximity)가 14 nm 임자에서 더 긴 것을 지시한다. 본 연구결과를 통하여 현재까지 알려지지 않은 규산염 나노입자의 입자의기에 의한 다양한 원자 구조의 변화를 규명하였다.

• Bulletin of the Korean Chemical Society
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• 제32권10호
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• pp.3712-3719
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• 2011

Confined Pt and $CoFe_2O_4$ nanoparticles (NPs) in a mesoporous core/shell silica microsphere, Pt-$CoFe_2O_4$@meso-$SiO_2$, were prepared using a bi-functional linker molecule. A large number of Pt NPs in Pt-$CoFe_2O_4$@meso-$SiO_2$, ranging from 5 to 8 nm, are embedded into the shell and some of them are in close contact with $CoFe_2O_4$ NPs. The hydrogenation of cyclohexene over the Pt-$CoFe_2O_4$@meso-$SiO_2$ microsphere at $25^{\circ}C$ and 1 atm of $H_2$ yields cyclohexane as a major product. In addition, it gives oxygenated products. Control experiments with $^{18}O$-labelled water and acetone suggest that surface-bound oxygen atoms in $CoFe_2O_4$ are associated with the formation of the oxygenated products. This oxidation reaction is operative only if $CoFe_2O_4$ and Pt NPs are in close contact. The Pt-$CoFe_2O_4$@meso-$SiO_2$ catalyst is separated simply by a magnet, which can be re-used without affecting the catalytic efficiency.

• Bulletin of the Korean Chemical Society
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• 제33권8호
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• pp.2546-2552
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• 2012

A novel biguanide-functionalized $Fe_3O_4/SiO_2$ magnetite nanoparticle with a core-shell structure was developed for utilization as a heterogeneous organosuperbase in chemical transformations. The structural, surface, and magnetic characteristics of the nanosized catalyst were investigated by various techniques such as transmission electron microscopy (TEM), powder X-ray diffraction (XRD), vibrating sample magnetometry (VSM), elemental analyzer (EA), thermogravimetric analysis (TGA), $N_2$ adsorption-desorption (BET and BJH) and FT-IR. The biguanide-functionalized $Fe_3O_4/SiO_2$ nanoparticles showed a superpara-magnetic property with a saturation magnetization value of 46.7 emu/g, indicating great potential for application in magnetically separation technologies. In application point of view, the prepared catalyst was found to act as an efficient recoverable nanocatalyst in nitroaldol and domino Knoevenagel condensation/Michael addition/cyclization reactions in aqueous media under mild condition. Additionally, the catalyst was reused six times without significant degradation in catalytic activity and performance.

• 한국산학기술학회논문지
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• 제17권9호
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• pp.1-11
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• 2016

본 연구에서는 벽면으로부터 균일한 열 유속 조건에서 나노유체의 층류유동에 의한 대류 열전달 향상과 관련하여 유동관 내 벽면에서의 나노입자 거동의 영향에 대한 수치해석 및 실험 연구에 대해서 논한다. $SiO_2$ 나노유체의 동적 열전도도는 스테인리스 원형 관(길이 1 m 및 직경 1.75 mm)의 외면에 부착된 T형 열전대를 활용하여 측정하였다. 실험에 사용된 나노유체는 직경이 24 nm인 구형의 $SiO_2$ 나노 입자를 초순수에 분산시켜 제조하였다. 나노 유체의 향상된 열전도도(즉, 최대 7.9 %의 증가)는 기본유체(즉, 초순수)와 나노유체 간 유동에서 벽면 온도 변화를 측정하여 비교함으로써 확인하였다. 하지만, 수치해석 결과에서는 실험으로부터 발견된 경향이 발견되지 못했는데, 이는 수치해석 모델이 기본적으로 연속체역학 및 안정된 콜로이드 용액에 나노 입자를 포함하는 유동특성에 기반을 두기 때문으로 분석된다. 이에 따라, 열교환 표면에서 나노입자와 벽면 간 상호작용(예: 나노입자의 고립된 침전)에 의한 표면특성 변화와 같은 비연속체역학 기반의 효과를 확인하기 위하여, 나노유체의 흐름 직후 정제수를 활용한 추가실험을 수행하였다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2005년도 춘계학술발표대회 및 제8회 신소재 심포지엄 논문개요집
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• pp.219-219
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• 2005

• 한국재료학회:학술대회논문집
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• 한국재료학회 2005년도 춘계학술발표대회 및 제8회 신소재 심포지엄 논문개요집
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• pp.308-308
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• 2005

• Bulletin of the Korean Chemical Society
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• 제31권12호
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• pp.3593-3599
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• 2010

In an original effort, this lab attempted to employ polystyrene nanoparticles as a template for the synthesis of ordered and highly porous macroporous $SiO_2$ thin films, utilizing their high combustion temperature and narrow size distribution. However, polystyrene nanoparticle thin films were not obtained due to the low interaction between individual particles and between the particle and silicon substrate. However, polystyrene-polyacrylic acid (PS-AA) colloidal particles of a core-shell structure were synthesized by a one-pot miniemulsion polymerization approach, with hydrophilic polyacrylic acid tails on the particle surface that improved interaction between individual particles and between the particle and silicon substrate. The PS-AA thin films were spin-coated in the thickness ranges from monolayer to approximately $1.0\;{\mu}m$. Using the PS-AA thin films as sacrificial templates, macroporous $SiO_2$ thin films were successfully synthesized by vapor deposition or conventional solution sol-gel infiltration methods. Inspection with field emission scanning electron microscopy (FE-SEM) showed that the macroporous $SiO_2$ thin films consist of interconnected air balls (~100 nm). Typical macroporous $SiO_2$ thin films showed ultralow refractive indices ranging from 1.098 to 1.138 at 633 nm, according to the infiltration conditions, which were confirmed by spectroscopy ellipsometry (SE) measurements. This research shows how the synthetic control of the macromolecule such as hydrophilic polystyrene nanopaticles and silicate sol precursors innovates the optical properties and processabilities for actual applications.