• Korean Chemical Engineering Research
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• 제53권1호
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• pp.78-82
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• 2015

유기주형(organic template) 입자를 이용하여 소디움실리케이트(sodium silicate)로부터 중공형 실리카(hollow silica) 입자를 제조하였다. 유기주형 입자로는 스티렌 단량체(styrene monomer)로부터 분산중합(dispersion polymerization)에 의해 제조된 폴리스티렌 라텍스(polystyrene latex, PSL) 입자를 사용하였다. 유기주형 입자 제조 시 중합개시제인 2,2'-azobisisobutyronitrile(AIBN)의 주입량을 조절하여 $1{\sim}3{\mu}m$의 크기를 가진 입자를 제조하였다. 생성된 유기주형 입자 표면에 졸-겔(sol-gel)법에 의해 소디움실리케이트로부터 생성된 실리카($SiO_2$) 나노 입자를 코팅하여 PSL/$SiO_2$ 코어-쉘 형태의 입자를 제조하였다. 유기용매인 테트라하이드로푸란(tetrahydrofuran, THF)을 이용하여 코어-쉘 입자 내부의 유기주형을 제거 하였다. 코어-쉘 입자 제조 시 용매의 종류 및 pH의 변화에 따라 생성되는 중공형 실리카 입자의 형상을 조사하였다. PSL/$SiO_2$ 코어-쉘 입자 제조 시 용매를 에탄올에서 물로 변경했을 때 중공형 실리카 입자가 성공적으로 제조되었으며 낮은 pH 값을 갖는 용매에서 쉘 두께가 균일한 중공형 실리카 입자가 형성되었다. 중공형 실리카 입자의 반사도를 측정한 결과 상용 제품(Insuladd)보다 높은 반사 특성을 보여주었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.281-281
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• 2010

Very low refractive index (<1.4) materials have been proved to be the key factor improving the performance of various optical components, such as reflectors, filters, photonic crystals, LEDs, and solar cell. Highly porous SiO2 are logically designed for ultralow refractive index materials because of the direct relation between porosity and index of refraction. Among them, ordered macroporous SiO2 is of potential material since their theoretically low refractive index ~1.10. However, in the conventional synthesis of ordered macroporous SiO2, the time required for the crystallization of organic nanoparticles, such as polystyrene (PS), from colloidal solution into well ordered template is typical long (several days for 1 cm substrate) due to the low interaction between particles and particle - substrate. In this study, polystyrene - polyacrylic acid (PS-AA) nanoparticles synthesized by miniemulsion polymerization method have hydrophilic polyacrylic acid tails on the surface of particles which increase the interaction between particle and with substrate giving rise to the formation of PS-AA film by simply spin - coating method. Less ordered with controlled thickness films of PS-AA on silicon wafer were successfully fabricated by changing the spinning speed or concentration of colloidal solution, as confirmed by FE-SEM. Based on these template films, a series of macroporous SiO2 films whose thicknesses varied from 300nm to ~1000nm were fabricated either by conventional sol - gel infiltration or gas phase deposition followed by thermal removal of organic template. Formations of SiO2 films consist of interconnected air balls with size ~100 nm were confirmed by FE-SEM and TEM. These highly porous SiO2 show very low refractive indices (<1.18) over a wide range of wavelength (from 200 to 1000nm) as shown by SE measurement. Refraction indices of SiO2 films at 633nm reported here are of ~1.10 which, to our best knowledge, are among the lowest values having been announced.

• 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.

• 멤브레인
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• 제26권5호
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• pp.381-390
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• 2016

본 연구에서는 고순도의 모데나이트(Mordenite) 입자를 합성하기 위하여 천연 제올라이트를 시드로 사용하여 시드의 농도 및 수열합성 시간에 따른 천연 제올라이트 시드가 합성에 미치는 영향을 고찰하였다. 그 결과 시드가 입자의 형성에 큰 영향을 끼치는 것을 확인할 수 있었고 시드를 3 g/100 g batch 주입하여 $140^{\circ}C$에서 72시간 동안 수열합성을 진행하였을 때 $1-2{\mu}m$ 사이즈의 고순도 모데나이트 입자를 합성할 수 있었다. 이를 통해 모데나이트 입자의 성장 기구를 규명할 수 있었으며, 모데나이트 입자 형성에 있어 시드는 첫째, 구형 모데나이트 전구체 형성 자리 공급의 역할과, 둘째 모데나이트 원료 물질 소스 역할을 한다는 것을 알 수 있었다. 합성된 모데나이트 입자의 가스 흡착량 분석 결과 $CO_2$ 기체의 흡착량이 97.19 mg/g로 다른 가스들에 비해 비교적 높은 흡착성능을 보였으며, $CO_2/H_2$의 선택도가 가장 우수한 것으로 나타났다. 따라서 이러한 결과들을 바탕으로 용도에 맞는 고순도 상의 모데나이트 입자를 합성할 수 있음을 확인하였고 보다 낮은 가격으로 우수한 분리성능을 갖는 분리막 소재개발에 활용할 수 있을 것이라 판단된다.

• Bulletin of the Korean Chemical Society
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• 제34권2호
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• pp.447-452
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• 2013

In this study we report a new method for the synthesis of a silica monolithic column bed with bimodal pores (throughpores and mesopores). The template induced synthesis method was used to direct bimodal pores simultaneously instead of the usual post base-treating method. Block polymer Pluronic F127 was chosen as a dual-function template to form hierarchically porous silica monolith with both macropores and mesopores. This is a simplification of the method of monolithic column preparation. Poly(ethylene glycol) was used as a partial substitute for F127 can effectively prevent shrinkage during the monolith aging process without losing much surface area (944 $m^2/g$ to 807 $m^2/g$). More importantly, the resultant material showed a much narrower mesopore size (centered at 6 nm) distribution than that made using only F127 as the template reagent, which helps the mass transfer process. The solvent washing method was used to remove the remaining organic template, and it was proved to be effective enough. The new synthesis method makes the fabrication of the silica monolithic column (especially capillary column) much easier. All the structure parameters indicate that monolith PFA05 prepared by the above method is a good material for separation, with the merits of much higher surface area than usual commercial HPLC silica particles, suitable mesopore volume, narrow mesopore size distribution, low shrinkage and it is easily prepared.

• Korean Chemical Engineering Research
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• 제45권6호
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• pp.611-618
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• 2007

아민기로 코팅된 단분산 폴리스티렌 입자를 제조한 뒤 톨루엔-물로 구성된 유중수 액적(oil-in-water emulsion) 내부에서 입자를 자기 조립(self-assembly)시켜 다양한 다면체(polyhedra) 구조의 콜로이드 클러스터(colloidal cluster)를 제조하였다. 콜로이드 클러스터의 표면에서 솔-젤(sol-gel) 반응을 유발한 뒤 표면이 실리카로 코팅된 복합(composite) 콜로이드 클러스터를 제조할 수 있었고 이를 주형(template)으로 활용하여 고온 소성에 의해 내부의 폴리스티렌 입자를 제거하고 마이크로미터 크기의 다양한 구조의 비구형상 공동 입자(hollow particle)를 제조하였다. 밀도구배원심분리법 (density gradient centrifugation)에 의해 폴리스티렌 구성 입자의 수와 구조가 균일한 콜로이드 클러스터를 제조할 수 있었으며 표면 솔-젤 반응에 의해 비구형상 구조의 공동 입자를 제조하였다.

• 한국입자에어로졸학회지
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• 제8권2호
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• pp.89-95
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• 2012

Spherical mesoporous silica particles, of which main pore diameter was 3.8 nm, were successfully prepared by spray pyrolysis from aqueous silicic acid. The effect of precursor concentration, reaction temperature, and the addition of urea and PEG on the particle diameter and pore properties such as pore diameter, total pore volume, and specific surface area were investigated by using FE-SEM, particle size analyzer, and nitrogen absorption-desorption analysis. With an increase of the precursor concentration from 0.2 M to 0.7 M, the average particle diameter, total pore volume, and specific surface area of the porous silica particles increased from 0.56 to $0.96\;{\mu}m$, 0.434 to $0.486\;cm^3/g$, 467.8 to $610.4\;m^2/g$, respectively. Within the temperature range $(600\;^{\circ}C{\sim}800\;^{\circ}C)$, there was no significant difference in the pore diameter, total pore volume, and specific surface area. In addition, the addition of urea as an expansion aid led to slight increases in particle diameter, pore diameter, and specific surface area. However, when the polyethylene glycol (PEG) as an organic template was used, the total pore volume of porous particles increased dramatically.

• 한국재료학회지
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• 제25권3호
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• pp.144-148
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• 2015

Cubic mesocrystal $CeO_2$ was synthesized via a hydrothermal method with glutamic acid ($C_5H_9NO_4$) as a template. The XRD pattern of a calcined sample shows the face-centered cubic fluorite structure of ceria. Transmission electron microscopy (TEM) and the selected-area electron diffraction (SAED) pattern revealed that the submicron cubic mesocrystals were composed of many small crystals attached to each other with the same orientation. The UV-visible adsorption spectrum exhibited the red-shift phenomenon of mesocrystal $CeO_2$ compared to commercial $CeO_2$ particles; thus, the prepared materials show tremendous potential to degrade organic dyes under visible light illumination. With a concentration of a rhodamine B solution of 20 mg/L and a catalyst amount of 0.1 g/L, the reaction showed higher photocatalytic performance following irradiation with a xenon lamp (${\geq}380nm$). The decoloring rate can exceed 100% after 300 min.

• Carbon letters
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• 제18권
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• pp.30-36
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• 2016

Well-dispersed Ag₃VO₄ nanoparticles @polyacrylonitrile (PAN) nanofibers were synthesized by an easily controlled, template-free method as a photo-catalyst for the degradation of methylene blue. Their structural, optical, and photocatalytic properties have been studied by X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy equipped with rapid energy dispersive analysis of X-ray, photoluminescence, and ultraviolet-visible spectroscopy. The characterization procedures revealed that the obtained material is PAN nanofibers decorated by Ag₃VO₄ nanoparticles. Photocatalytic degradation of methylene blue investigated in an aqueous solution under irradiation showed 99% degradation of the dye within 75 min. Finally, the antibacterial performance of Ag₃VO₄ nanoparticles @PAN composite nanofibers was experimentally verified by the destruction of Escherichia coli. These results suggest that the developed inexpensive and functional nanomaterials can serve as a non-precious catalyst for environmental applications.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.8.1-8.1
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• 2011

Nanocrystalline titanium dioxide ($TiO_2$) materials have been widely used as an electron collector in DSSC. This is required to have an extremely high porosity and surface area such that the dye can be sufficiently adsorbed and be electronically interconnected, resulting in the generation of a high photocurrent within cells. In particular, their geometrical structures and crystalline phase have been extensively investigated as important issues in improving its photovoltaic efficiency. In this study, we present a new strategy to fabricate a photoelectrode having a periodic structured $TiO_2$ film templated from 1D or 3D polystyrene (PS) microspheres array. Monodisperse PS spheres of various radiuses were used for colloidal array on FTO glasses and two types of photoelectrode structures with different $TiO_2$ materials were investigated respectively. One is the igloo-shaped electrode prepared by $TiO_2$ deposition by RF-sputtering onto 2D microsphere-templated substrates. At the interface between the film and substrate, there are voids formed by the decomposition of PS microspheres during the calcination step. These holes might be expected to play the predominant roles as scattering spherical voids to promote a light harvesting effect, a spacious structure for electrolytes with higher viscosity and effective paths for electron transfer. Additionally the nanocrystalline $TiO_2$ phase prepared by the RF-sputtering method was previously reported to improve the electron drift mobility within $TiO_2$ electrodes. This yields solar cells with a cell efficiency of 2.45% or more at AM 1.5 illumination, which is a very remarkable result, considering its $TiO_2$ electrode thickness (<2 ${\mu}m$). This study can be expanded to obtain higher cell efficiency by higher dye loading through the increase of surface area or multi-layered stacking. The other is the inverse opal photonic crystal electrode prepared by titania particles infusion within 3D colloidal arrays. To obtain the enlargement of ordered area and high quality of crystallinity, the synthesis of titania particles coated with a organic thin layer were applied instead of sol-gel process using the $TiO_2$ precursors. They were dispersed so well in most solvents without aggregates and infused successfully within colloidal array structures. This ordered mesoporous structure provides the large surface area leading to the enough adsorption of dye molecules and have an light harvesting effect due to the photonic band gap properties (back-and-forth reflection effects within structures). A major advantage of this colloidal array template method is that the pore size and its distribution within $TiO_2$ photoelectrodes are determined by those of latex beads, which can be controlled easily. These materials may have promising potentials for future applications of membrane, sensor and so on as well as solar cells.