Nb2O5 nanowire array photoanode sensitized by composition-tuned CdSxSe1-x shell

강준하 Graduate School, Korea University 2012 국내석사

Vertically-aligned Nb2O5 nanowires (NW) were grown by the thermal oxidation of Nb foils. The thermal chemical vapor transport of CdS/CdSe powders produces Nb2O5-CdSxSe1-x core-shell NW arrays with complete composition tuning. In the alloy composition, CdSe-like and CdS-like phases exist in the outer and inner regions of the shell, respectively, forming unique multi-shell structures. As x increases, the thickness of the CdSe-like outer shell decreases, while that of the CdS-like inner shell increases. We fabricated photoelectrochemical (PEC) cells using the as-grown Nb2O5-CdSxSe1-x NW arrays and measured their photocurrents and hydrogen generation rates under AM 1.5G irradiation. The PEC cells showed excellent photoconversion efficiency, which is comparable to that of TiO2-CdSxSe1-x NW arrays. It indicates that the present Nb2O5 NW array promises an excellent photoanode of solar cell devices. The multi-shell structures increase the PEC performance by producing novel band alignment for efficient electron-hole separation following enhanced visible-range photon absorption.

열을 고려한 에어 포일 스러스트 베어링의 다중 물리 연동 해석

文昭娟 영남대학교 대학원 2024 국내석사

In this study, air foil thrust bearings is analized that support axial loads using air as the lubricating fluid among sliding bearings. Air foil thrust bearings are widely employed in high-speed rotation systems due to their advantages of low friction and heat generation associated with using air as the lubricating fluid. Heat generation becomes significant under ultra-high-speed conditions. The resulting heat affects foil bearing deformation, lubricant viscosity, and thin film pressure, leading to results significantly different from isothermal conditions. Therefore, this thesis employs COMSOL Multiphysics to perform multi-physics analysis, considering heat, on air foil thrust bearings. For thermal lubrication analysis, a generalized Reynolds equation considering variations in fluid viscosity and density along the film thickness direction is adopted. Additionally, an energy equation is employed to determine temperature distribution, enabling the analysis of conduction, convection, work of compressibility, and viscous dissipation. As a result, when considering heat, the bearing performance is interpreted to be superior to isothermal air foil thrust bearings. Thin film pressure is much higher when heat analysis is added under all identical conditions. Deformation of bump foil and top foil is calculated to be greater due to thermal deformation compared to elastic deformation alone. This is attributed to the interdependence of film pressure, heat transfer, and foil elastic deformation in the coupled thermal-fluid-structure analysis. These all results give the insight that considering heat to derive more accurate bearing performance, heat analysis is essential.

Synthesis of magnetic and fluorescent core-shell type coordination polymer particles

김유나 연세대학교 대학원 2014 국내석사

최근 많은 연구가 진행되고 있는 금속-유기 복합체 (Metal - Organic framework, MOF)는 금속이온과 유기 리간드가 배위하여 1-D, 2-D 또는 3-D의 무한한 구조를 가지는 물질을 말한다. 구조의 가장 큰 특징은 기공(Pore)을 가지고 있다는 것이며, 이 기공을 이용하여 무기 및 탄소 재료와 함께 다공성 물질의 한 분야로 다양한 연구가 진행되고 있다. MOF에 관한 연구는 주로 bulk한 단결정 위주로 발전해왔으나 최근에는 배위고분자 물질의 장점과 나노화학의 장점을 접목시킨 연구가 큰 관심을 받고 있다. 배위고분자 물질을 입자화 (Coordination Polymer Particles, CPPs)하면, 입자를 마이크로 혹은 나노크기로 구현시킴으로써 생기는 새로운 화학적, 물리적 특성으로 인해 보다 많은 분야로의 응용이 확대될 것으로 기대된다. 또한, 배위고분자 물질은 사용하고자 하는 용도에 따라 배위고분자 입자의 구성 성분이 되는 리간드를 선택하여 입자화 할 수 있기 때문에 보다 쉽게 리간드 또는 금속이 가지고 있는 고유한 기능성을 배위고분자 입자에 부여할 수 있다. 구성 성분뿐만 아니라 배위고분자 입자의 모양과 크기 제어 또한 배위고분자 입자의 특성을 조절할 수 있는 중요한 요소로서, 이에 대한 형성 메커니즘과 형태 조절에 관한 많은 연구가 선행되고 있다. 이러한 배위고분자의 다양한 장점들을 이용한다면 맞춤형 입자로의 합성과 그에 따른 물리적, 화학적 특성 조절이 가능하게 된다. 이에 본 연구실에서는 배위고분자의 응용성을 극대화하기 위해 최근 배위고분자와 고형물(Solid Material)과의 융합을 통한 하이브리드 물질(Hybrid Material)을 코어-쉘의 형태로 합성하려는 연구가 진행되고 있다. 뿐만 아니라, 배위고분자 입자를 전구물질로 이용하여 간단하게 열처리하는 방법(Calcination Process)을 통해 금속산화물로의 새로운 합성 방법론을 개척하였으며, 이를 이용하여 금속산화물의 광학적, 전기적, 자기적 성질을 조절하는 연구가 진행 중이다. 본 연구에서는 대표적인 Solid material인 magnetite(Fe3O4)와 Silica를 코어로 이용하여 독특한 형광 또는 자성이 있는 배위고분자 쉘을 성장시킴으로써 코어-쉘 형태의 다기능성 입자를 형성하였다. 그리고 코어-쉘 실리카@배위고분자로부터 열처리 과정을 통해 금속산화물을 합성하였다. 향후 실리카만을 선택적으로 녹여내는 에칭과정을 거친다면 속이 빈 형태의 금속산화물을 얻을 수 있을 것으로 기대되며 독특한 내부 구조적 특성을 동시에 지닌 다기능성 물질(Multi-functional Material)로서, 촉매, 약물 전달, 에너지 저장 등과 같은 보다 다양한 응용 분야에 적용 가능할 것이다.

코어쉘 구조를 가지는 고 열전도성 및 전기 절연성의 PPS 복합재료

김세민 서울대학교 대학원 2021 국내석사

Polyphenylene sulfide (PPS) is an outstanding material as an engineering thermoplastic polymer for diverse industrial applications. We investigated a highly thermally conductive PPS composite containing muti-walled carbon nanotubes (MWCNTs) and aluminum nitride (AlN) as a thermally conductive filler. For a stable formation of heat flow channel, the PPS composite was prepared by core-shell fabrication method in order to obtain high thermal conductivity with low filler contents, and thus overcome the demerits of melt mixing fabrication method. A comparison between conventionally melt mixed composite and the proposed core-shell composite showed that the consecutive chain of filler at the surface of each polymer pellet could enhance the thermal conductivity very much. Moreover, the thickness of the AlN coating layer could be controlled by diluting the concentration of the adhesive epoxy resin using acetone as the solvent. AlN/PPS core-shell pellets with various thicknesses were fabricated in order to analyze the effect of the coating layer’s thickness on thermal conductive properties. A 1:0.2 weight ratio of epoxy and acetone has the highest thermal conductivity enhancement ratio compared to the melt mixed composite, and the optimum AlN contents of c-AlN(0.2) was 19 wt% from TGA analysis. Hereafter, we fabricated PPS/MWCNTs/AlN composites via melt mixing and core-shell fabrication. The characteristics of composite materials according to fabrication method were compared and analyzed by FE-SEM, EDS, thermal conductivity analysis, TGA, void fraction analysis and tensile strength measurement. Compared to the composite materials fabricated by melting mixing method, it was confirmed that the thermal conductivity values were improved by more than 2.5 times in the core-shell composite materials containing the same amount of thermal conductive fillers. The composite material with the highest thermal conductivity improvement rate was found to be a core-shell composite material containing 2 wt% MWCNTs. The electrically insulating AlN layer efficiently hindered a conduction of electron, which is the main problem with utilizing MWCNTs as a thermally conductive filler in polymer composites, in spite of their remarkable thermal conductivity. As a result, all core-shell composite materials showed electrical conductivity values of 10-8 S/cm or less, and all of the composite materials fabricated by melt mixing method showed electrical conductivity values of 10-8 S/cm or higher, indicating that core-shell composite materials had electrical insulating properties. Therefore, core-shell fabrication method may be used as a promising composite fabrication method for engineering plastic based thermally conductive materials, forming a 3D heat flow channels with electrically insulating effect. 본 연구에서는 폴리페닐렌설파이드에 뛰어난 열전도 특성을 가지는 카본나노튜브와 질화알루미늄을 보강재로 도입하고, 안정적인 열 흐름 통로의 형성을 위해 코어쉘 구조를 가지는 방열 고분자 복합재료를 제조하고 제조 방법에 따른 특성을 분석하였다. 먼저, 질화알루미늄 파우더 코팅 층의 두께에 따른 복합재료의 열전도도 특성 변화를 분석하기 위해 아세톤을 사용하여 에폭시 레진의 농도를 조절하며 코어쉘 복합재료를 제조하였다. 그 결과, 에폭시 레진과 아세톤의 중량 비율이 1:0.2인 조건에서 가장 높은 열전도도 향상률을 확인하였으며, 약19 wt%의 질화알루미늄 함량을 확인하였다. 폴리페닐렌설파이드/ 카본나노튜브/질화알루미늄 복합재료를 용융 블렌드 방식과 코어쉘 제조 방식으로 각각 제조하였다. FE-SEM, EDS, 열전도성 분석, 열 중량 분석, 공극률 분석, 기계적 특성 분석을 통해 제조 방식에 따른 복합재료의 특성을 비교 분석하였다. 용융 혼합법으로 제조한 복합재료에 비해, 동량의 열전도성 보강재가 함유된 코어쉘 복합재료에서 열전도도 값이 2.5배 이상 향상됨을 확인하였다. 가장 열전도도 향상률이 높은 복합재료는 카본나노튜브를 2 wt% 함유한 코어쉘 복합재료로 나타났다. 카본나노튜브가 유발할 수 있는 전자의 전도를 전기 절연성의 질화알루미늄 코팅 층이 효과적으로 차단하는지 확인하기 위하여, 고 저항 미터기를 사용하여 복합재료의 전기 전도도를 측정하였다. 코어쉘 복합재료는 모두 10-8 S/cm 이하의 전기 전도도 값을 나타냈고, 용융 블렌드 방식으로 제조한 복합재료는 모두 10-8 S/cm 이상의 전기 전도도 값을 나타내어 코어쉘 복합재료가 전기 절연 특성을 가짐을 확인하였다.

Facile synthesis and structural control of multi-component metallic nanomaterials

최은진 Seoul National University 2016 국내박사

Noble metal nanoparticles exhibit unique physical and chemical properties that are highly dependent on their size, shape, and chemical composition. During the last few decades, intensive research has been focused on the development of various synthetic methods for producing uniform nanoparticles and the precise control of their size and shape. Recently, multi-component metallic nanomaterials have attracted much attention for their great potential application in catalysis, sensor, and biomedical application. These nanomaterials can have not only the individual characteristics of the different components, but also new and unexpected properties arising from the synergistic effect between them. In this dissertation, facile and structure-controllable synthesis of multi-component metallic nanomaterials were studied. Firstly, Ag-Cu core-shell and alloy bimetallic nanoparticles (NPs) were prepared by a solventless mix-bake-wash method. The simple one-step heating process was assisted by salt powder as a template, obtaining small bimetallic nanomaterials. The particle structure could be controlled by tuning the annealing temperature to generate hetero-structured core-shell NPs or homogeneous alloys. Whereas the as-synthesized Ag@Cu core-shell NPs consist of a core of face-centered cubic (fcc) polycrystalline Ag NPs and a shell of fcc Cu including trace amounts of copper oxides, the AgCu nanoalloy was found to comprise a single-phase NP with the same crystal structure as that of Ag, without the copper oxide species. Cyclic voltammetric measurements confirmed the chemical identification of the surface species and their stability to oxidation. Secondly, rattle-structured nanomaterials composed of a gold nanorod in a mesoporous silica nanocapsule (AuNR@mSiO2) were prepared by a novel solution-based consecutive process. Uniform-sized gold NRs were encapsulated inside a silver nanoshell, followed by SiO2 coating through the sol-gel technique. After selectively etching away the silver inner layer, a rattle-structured nanomaterial was obtained. The AuNR@mSiO2 rattle-shaped nanostructures were highly uniform in morphology, and the inner hollow space and the thickness of the mesoporous silica layer were easily controlled by adjusting the amount of each chemical agent. The drug-loading properties of the nanomaterial and the regrowth control of the core nanoparticles were also studied.