• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.217-217
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• 2011

Recently, demand for thermally stable metal nanoparticles suitable for chemical reactions at high temperatures has increased to the point to require a solution to nanoparticle coalescence. Thermal stability of metal nanoparticles can be achieved by adopting core-shell models and encapsulating supported metal nanoparticles with mesoporous oxides [1,2]. However, to understand the role of metal-support interactions on catalytic activity and for surface analysis of complex structures, we developed a novel catalyst design by coating an ultra-thin layer of titania on Pt supported silica ($SiO_2/Pt@TiO_2$). This structure provides higher metal dispersion (~52% Pt/silica), high thermal stability (~600$^{\circ}C$) and maximization of the interaction between Pt and titania. The high thermal stability of $SiO_2/Pt@TiO_2$ enabled the investigation of CO oxidation studies at high temperatures, including ignition behavior, which is otherwise not possible on bare Pt nanoparticles due to sintering [3]. It was found that this hybrid catalyst exhibited a lower activation energy for CO oxidation because of the metal-support interaction. The concept of an ultra-thin active metal oxide coating on supported nanoparticles opens-up new avenues for synthesis of various hybrid nanocatalysts with combinations of different metals and oxides to investigate important model reactions at high-temperatures and in industrial reactions.

• 한국표면공학회지
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• 제48권4호
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• pp.158-162
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• 2015

To substitute indium tin oxide (ITO), many substituents have been studied such as metal nanowires, carbon based materials, 2D materials, and conducting polymers. These materials are not good enough to apply to an electrode because theses exhibit relatively high resistance. So metal grids are required as an additionalelectrode to improve the conductivities of substituents. The metal grids were printed by electrohydrodynamic printing system using Ag nanoparticle based ink. The Ag grids showed high uniformity and the line width was about $10{\mu}m$. The Ag nanoparticles are surrounded by dispersants such as unimolecular and polymer to prevent aggregation between Ag nanoparticles. The dispersants lead to low conductivity of Ag grids. Thus, the sintering process of Ag nanoparticles is strongly recommended to remove dispersants and connect each nanoparticles. For sintering process, the interface and microstructure of the Ag grid were controlled in 1.0 torr Ar atmosphere at aound $400^{\circ}C$ of temperature. From the sintering process, the uniformity of the Ag grid was improved and the defects on the Ag grids were reduced. As a result, the resistivity of Ag grid was greatly reduced up to $5.03({\pm}0.10){\times}10^{-6}{\Omega}{\cdot}cm$. The metal grids embedded substrates containing low pressure Ar sintered Ag grids showed 90.4% of transmittance in visible range with $0.43{\Omega}/{\square}$ of sheet resistance.

• Bulletin of the Korean Chemical Society
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• 제34권11호
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• pp.3301-3306
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• 2013

This paper aims to address the cellular toxicity of ultra-pure titanium dioxide ($TiO_2$) and zinc oxide (ZnO) nanoparticles (NPs) frequently employed in sunscreens as inorganic physical sun blockers to provide protection against adverse effects of ultraviolet (UV) radiation including UVB (290-320 nm) and UVA (320-400 nm). In consideration that the production and the use of inorganic NPs have aroused many concerns and controversies regarding their safety and toxicity and that microsized $TiO_2$ and ZnO have been increasingly replaced by $TiO_2$ and ZnO NPs (< 100 nm), it is very important to directly investigate a main problem related to the intrinsic/inherent toxicity of these NPs and/or their incompatibility with biological objects. In the present study, we took advantage of the laser-assisted method called laser ablation for generation of $TiO_2$ and ZnO NPs. NPs were prepared through a physical process of irradiating solid targets in liquid phase, enabling verification of the toxicity of ultra-pure NPs with nascent surfaces free from any contamination. Our results show that $TiO_2$ NPs are essentially non-poisonous and ZnO NPs are more toxic than $TiO_2$ NPs based on the cell viability assays.

• 폴리머
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• 제27권6호
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• pp.576-582
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• 2003

열가소성 수지인 폴리프로필렌과 나일론 블렌드를 무기나노입자인 몬모릴로나이트와 상용화제 말레산 무수물 폴리프로필렌을 사용하여 복합화한 나노복합재료에 할로젠 계열의 난연제 데카브로모다이페닐옥사이드를 첨가하였을 때의 분산성과 난연특성 및 기계적 특성의 향상에 대해 실험하였다. 고분자 수지의 난연특성과 기계적 특성은 난연제의 첨가뿐만 아니라 나노복합화를 통해서도 향상될 수 있으며, 고분자 수지 내의 나노입자의 분산정도에 따라 매우 큰 차이가 생긴다. 고분자 수지와 무기나노입자 사이의 분산성과 그에 따른 난연특성 및 기계적 특성을 난연제와 무기나노입자의 함량에 .따라 정량적으로 측정하였다 폴리프로필렌/나일론 블렌드를 몬모릴로나이트로 복합화할 때 2회 이상 컴파운딩하면 완전히 분산되는 것을 XRD 결과로 확인하였다. 폴리프로필렌/나일론 블렌드를 복합화하면 나일론의 첨가로 인한 난연성의 저하를 극복할 수 있었으며, 무기나노입자가 완전히 분산되어 있을 때에는 추가적인 난연특성의 향상을 얻었다. 그리고 폴리프로필렌은 나일론의 첨가로 인하여 인장강도와 충격강도가 약간 증가하였으며, 무기나노입자와의 복합화를 통해서 추가적인 기계적 물성의 증가를 관찰하였다. 이로부터 폴리프로필렌의 기계적 물성의 향상을 위해 첨가한 나일론은 난연특성의 저하를 초래하지만 무기나노입자와의 복합화를 통해 난연특성의 향상과 추가적인 기계적 물성의 향상을 동시에 얻을 수 있었다.

• Journal of Microbiology and Biotechnology
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• 제24권1호
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• pp.87-96
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• 2014

In the present study, a yeast species isolated from CETP, Vellore, Tamilnadu was identified as Cryptococcus sp. VITGBN2 based on molecular techniques and was found to be a potent producer of acidic diacetate sophorolipid in mineral salt media containing vegetable oil as additional carbon source. The chemical structure of the purified biosurfactant was identified as acidic diacetate sophorolipid through GC-MS analysis. This sophorolipid was used as a stabilizer for synthesis of zinc oxide nanoparticles (ZON). The formation of biofunctionalized ZON was characterized using UV-visible spectroscopy, XRD, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy. The antimicrobial activities of naked ZON and sophorolipid functionalized ZON were tested based on the diameter of inhibition zone in agar well diffusion assay, microbial growth rate determination, protein leakage analysis, and lactate dehydrogenase assay. Bacterial pathogen Salmonella enterica and fungal pathogen Candida albicans showed more sensitivity to sophorolipid biofunctionalized ZON compared with naked ZON. Among the two pathogens, S. enterica showed higher sensitivity towards sophorolipid biofunctionalized ZON. SEM analysis showed that cell damage occurred through cell elongation in the case of S. enterica, whereas cell rupture was found to occur predominantly in the case of C. albicans. This is the first report on the dual role of yeast-mediated sophorolipid used as a biostabilizer for ZON synthesis as well as a novel functionalizing agent showing antimicrobial property.

• Environmental Analysis Health and Toxicology
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• 제26권
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• pp.3.1-3.6
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• 2011

Objectives: Titanium dioxide ($TiO_2$), a common nanoparticle widely used in industrial production, is one of nano-sized materials. The purpose of this study was to determine the acute and chronic toxicity of $TiO_2$ using different size and various concentrations on Daphnia magna. Methods: In the acute toxicity test, four concentrations (0, 0.5, 4, and 8 mM) for $TiO_2$ with 250 or 500 nm and five concentrations (0, 0.25, 0.5, 0.75, and 1 mM) for $TiO_2$ with 21 nm were selected to analyze the toxic effect to three groups of ten daphnia neonates over 96 hours. In addition, to better understand their toxicity, chronic toxicity was examined over 21 days using 0, 1, and 10 mM for each type of $TiO_2$. Results: Our results showed that all organisms died before the reproduction time at a concentration of 10 mM of $TiO_2$. In addition, the exposure of anatase (21 nm) particles were more toxic to D. magna, comparing with that of anatase (250 nm) and rutile (500 nm) particles. Conclusions: This study indicated that $TiO_2$ had adverse impacts on the survival, growth and reproduction of D. magna after the 21days exposure. In addition, the number of test organisms that were able to reproduce neonates gradually were reduced as the size of $TiO_2$ tested was decreased.

• 대한환경공학회지
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• 제36권6호
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• pp.396-401
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• 2014

나노물질은 다양한 분야에 널리 사용되고 있다. 본 연구에서는 Lactuca(상추)와 Raphanus(알타리무) 씨앗의 발아와 발아지수에 금속산화물 나노입자(CuO, NiO, $Fe_2O_3$, $Co_3O_4$, $TiO_2$, ZnO)가 미치는 영향을 조사하였다. 용액상 노출에서 CuO가 가장 큰 영향을 나타내었으며, 발아와 발아지수의 $EC_{50}$는 각 0.46 mg/L와 0.37%로 조사되었다. 씨앗 이용 식물독성 측정에서 상추가 알타리무보다 나노입자 노출에 대해 더욱 민감한 반응을 나타내었다. 일반적으로 나노입자의 씨앗발아와 발아지수에 근거한 영향은 다음의 순서로 조사되었다: CuO > ZnO >NiO > $TiO_2$, $Fe_2O_3$, $Co_3O_4$. 특히 $TiO_2$, $Fe_2O_3$와 $Co_3O_4$는 최대 노출 농도 1,000 mg/L 농도에서도 뚜렷한 영향을 나타내지 않았다.

• 공업화학
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• 제27권2호
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• pp.145-152
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• 2016

본 연구에서는 전기화학적 바이오센서의 포도당 감지능을 높이고자 금 나노 입자가 분산된 다중벽탄소나노튜브(multi-walled carbon nanotube, MWCNTs)에 CuO를 도입하였다. 금 나노 입자로 인하여 나노 클러스터(cluster) 형상을 갖는 CuO가 합성되었으며, 이는 포도당 감지능력에 매우 큰 영향을 나타내었다. 0.1 mole의 CuO가 합성되었을 때 CuO/Au@MWCNTs 나노복합재를 전극재료로서 바이오센서는 $504.1{\mu}A\;mM^{-1}cm^{-2}$으로 가장 높은 민감도를 보여주었으며, 이 값은 MWCNTs만을 전극으로 이용할 때보다 약 4배 정도 컸다. 또한, 0-10 mM의 긴 선형 구간(linear range)과 0.008 mM의 낮은 LoD (limit of detection) 값을 보여주었다. 이러한 실험 결과들은 CuO/Au@MWCNTs 나노복합재가 CuO를 이용한 다른 전기화학적 바이오센서보다 우수하다는 것을 입증하였으며, 이는 나노 클러스터 형상의 CuO가 포도당 감지에서 전기화학적 반응에 유리하기 때문으로 사료된다.

• 한국분말재료학회지
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• 제26권4호
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• pp.327-333
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• 2019

In this study, a process is developed for 3D printing with alumina ($Al_2O_3$). First, a photocurable slurry made from nanoparticle $Al_2O_3$ powder is mixed with hexanediol diacrylate binder and phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide photoinitiator. The optimum solid content of $Al_2O_3$ is determined by measuring the rheological properties of the slurry. Then, green bodies of $Al_2O_3$ with different photoinitiator contents and UV exposure times are fabricated with a digital light processing (DLP) 3D printer. The dimensional accuracy of the printed $Al_2O_3$ green bodies and the number of defects are evaluated by carefully measuring the samples and imaging them with a scanning electron microscope. The optimum photoinitiator content and exposure time are 0.5 wt% and 0.8 s, respectively. These results show that $Al_2O_3$ products of various sizes and shapes can be fabricated by DLP 3D printing.

• Advances in nano research
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• 제12권1호
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• pp.73-79
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• 2022

Due to the extensive use of concrete structures in various applications, the improvement of their strength and quality has become of great importance. A new way of achieving this purpose is to add different types of nanoparticles to concrete admixtures. In this work, a mathematical model has been employed to analyze the vibration of concrete beams reinforced by graphene oxide (GO) nanoparticles. To verify the accuracy of the presented model, an experimental study has been conducted to compare the compressive strengths of these beams. Since GO nanoparticles are not readily dissolved in water, before producing the concrete samples, the GO nanoparticles are dispersed in the mixture by using a shaker, magnetic striker, ultrasonic devices, and finally, by means of a mechanical mixer. The sinusoidal shear deformation beam theory (SSDBT) is employed to model the concrete beams. The Mori-Tanaka model is used to determine the effective properties of the structure, including the agglomeration influences. The motion equations are calculated by applying the energy method and Hamilton's principle. The vibration frequencies of the concrete beam samples are obtained by an analytical method. Three samples containing 0.02% GO nanoparticles are made and their compressive strengths are measured and compared. There is a good agreement between our results and those of the mathematical model and other papers, with a maximum difference of 1.29% between them. The aim of this work is to investigate the effects of nanoparticle volume fraction and agglomeration and the influences of beam length and thickness on the vibration frequency of concrete structures. The results show that by adding the GO nanoparticles, the vibration frequency of the beams is increased.