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Direct Cd-to-Pb Exchange of CdSe Nanorods into PbSe/CdSe Axial Heterojunction Nanorods
Lee, Dongkyu,Kim, Whi Dong,Lee, Seokwon,Bae, Wan Ki,Lee, Sangheon,Lee, Doh C. American Chemical Society 2015 Chemistry of materials Vol.27 No.15
<P>We report synthesis of PbSe nanorods (NRs) and PbSe/CdSe axial heterojunction NRs via direct Cd-to-Pb cation exchange in CdSe NRs. Use of suited ligand–cation combinations enables the cation exchange while keeping the nanomaterial morphology intact. For example, solvation of Cd<SUP>2+</SUP> using oleylamine (OLA) allows for the cation exchange process, which would not be possible by using oleic acid instead of OLA. A mild cation exchange process, such as mixing Pb-oleate and OLA with CdSe NRs at 130 or 150 °C, results in anisotropic replacement of CdSe into PbSe along the ⟨0001⟩ direction of wurtzite CdSe, and a partial conversion leads to the formation of heterostructure NRs containing axial CdSe/PbSe heterojunctions. While the cation exchange proceeds at both tips of CdSe NRs, exchange appears to be faster on (0001̅) planes. Binding energy calculation based on density functional theory reveals that OLA binds strongly to the (0001̅) facet of CdSe NRs, leading to asymmetric cation exchange. This protocol to convert CdSe nanocrystals directly into PbSe broadens the design range of CdSe/PbSe heterojunction nanomaterials potentially with various morphologies because template CdSe nanocrystals can be prepared in different shapes via colloidal synthesis.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2015/cmatex.2015.27.issue-15/acs.chemmater.5b01548/production/images/medium/cm-2015-01548m_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm5b01548'>ACS Electronic Supporting Info</A></P>
Lee, Sooho,Lee, Kangha,Kim, Whi Dong,Lee, Seokwon,Shin, Do Joong,Lee, Doh C. American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.41
<P>In this study, we designed and synthesized photocatalysts for hydrogen evolution from water by coating a thin layer of amorphous TiO<SUB>2</SUB> (<I>a</I>-TiO<SUB>2</SUB>) on CdSe nanocrystals (NCs). The thin shell of <I>a</I>-TiO<SUB>2</SUB> serves as a channel for charge carriers otherwise unutilized. Albeit a previous notion that <I>a</I>-TiO<SUB>2</SUB> is a poor photocatalyst, the enhanced photocatalytic activity in the presence of <I>a</I>-TiO<SUB>2</SUB> suggests that the material helps utilize the photogenerated charge carriers when it is in a form of thin shell on CdSe NCs. Type II band offset in CdSe/<I>a</I>-TiO<SUB>2</SUB> appears to allow the electron in the conduction band of CdSe NCs to migrate over to that of <I>a</I>-TiO<SUB>2</SUB>, and the electron participates in the hydrogen production from water. Size of CdSe NCs influences the photocatalytic hydrogen evolution rate as the energy difference between the conduction bands of semiconductors becomes larger. Electron transfer from CdSe NCs to <I>a</I>-TiO<SUB>2</SUB> layer is influenced by the level of the conduction-band edge of CdSe NCs: the size dependence indicates that electron injection to TiO<SUB>2</SUB> is facilitated with energy level offset between CdSe and TiO<SUB>2</SUB>, while smaller NCs have larger band gap and thus narrower spectral range of absorption. The interplay between charge-transfer rate and absorption cross-section should be considered in designing heterostructure NC-based photocatalysts for water splitting.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-41/jp508315m/production/images/medium/jp-2014-08315m_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp508315m'>ACS Electronic Supporting Info</A></P>
Lee, Kangha,Lee, Cheol-Ho,Cheong, Jun Young,Lee, Seokwon,Kim, Il-Doo,Joh, Han-Ik,Lee, Doh Chang Springer-Verlag 2017 Korean Journal of Chemical Engineering Vol.34 No.12
<P>We report photoelectrochemical hydrogen evolution reaction using a Cu2O-based photocathode with a layer doped with Zn ions. The doping results in the shift of the onset flat-band potential of the photocathode, likely a consequence of maximized band-bending in the Cu2O/Zn : Cu2O heterojunction. Systematic electrochemical analysis reveals that expansion of depletion region is responsible for the enhanced photoelectrochemical performance, e.g., the increase of photocurrent and reduced internal resistance.</P>
A New type of Bolting Robot for Steel-frame structure Constructions
Seokwon Lee,Hyungdo Nam,Yongkwun Lee,Jonghyeon Park 제어로봇시스템학회 2008 제어로봇시스템학회 국제학술대회 논문집 Vol.2008 No.10
In this paper, a new type bolting robot in steel-frame structure is introduced. The robot is composed of 3-axis gantry arms with linear motion actuators, a bolting tool, a cabin and additional supporting parts. To construct a high-rise building, steel-frame structure is more suitable than reinforced concrete structures. In steel-frame constructions, it is demanded fasten bolts to join two beams. By using this bolting robot, it can improve the efficiency and safety of construction. This paper describes design of a new type bolting robot and its dynamical analysis with some experiments.
식품소재화를 위한 Calendula officinalis L. 꽃잎의 항피부노화 기능성 규명 및 비효소적 연화 기술 연구
임석원(Seokwon Lim),최성빈(Sungbin Choi),이범주(Pomjoo Lee),김형섭(Hyung-sup Kim),이다영(Da-young Lee),변상균(Sanguine Byun) 한국식품과학회 2019 한국식품과학회지 Vol.51 No.3
UVB에 의한 MMP-1의 과발현이 카렌듈라 꽃잎을 처리하여 주면 농도의존적으로 감소하였다. 이를 통해 연화시킨 카렌듈라 꽃잎이 UVB에 의한 피부의 광노화를 억제시킬 수 있다는 것을 확인하였다. 가열과 산처리의 복합처리를 통한 카렌듈라 꽃잎의 연화에서 처리시간, 온도, pH에 따른 연화 수준을 punctual test를 통해 비교 분석하였다. Hardness 값의 비료 분석을 통해 연화특성 및 효과가 처리 조건들에 의해 다름을 확인할 수 있었으며, 70℃ 이상의 높은 온도에 의한 연화효과가 산처리에 의한 효과보다 더 큰 것을 확인할 수 있었다. 하지만 열처리에 의한 연화의 경우 에너지 소비가 큰 것을 고려할 때, pH 2.1에서는 50℃, 30분의 열처리만으로도 70℃ 이상의 열처리 효과가 나타나므로, 이 연화처리 조건이 경제적으로 가장 효율적이라 판단되었다. Calendula (Calendula officinalis L.) petals are edible flowers which have been used as a decorative ingredient in dishes or as a medicinal food. In this study, the anti-skin aging potential of calendula petals was investigated. Additionally, the texture was softened by non-enzymatic methods to broaden their application as a food or cosmetic agent. Treatment of calendula prevented ultraviolet-induced matrix metalloproteinase-1 expression in skin cells. We investigated whether heating-based processing could soften calendula petals. The results from the punctual test demonstrated significant changes in the hardness of calendula petals depending on the pH, heating temperature, and time. Although there were minor differences among various processing conditions, the largest alteration in hardness was observed when the petals were softened by incubation at 80°C and pH 2.3 for 120 min. Collectively, these results show that the application of proper processing conditions can soften calendula petals without using enzymes.
3축 가속도 센서를 이용한 정확한 걸음 수 측정 방법 연구
이석원 ( Seokwon Lee ),김동화 ( Donghwa Kim ),박소영 ( Soyoung Park ),신지은 ( Jieun Shin ),신효원 ( Hyowon Shin ),서동만 ( Dongmahn Seo ) 한국정보처리학회 2016 한국정보처리학회 학술대회논문집 Vol.23 No.2
최근 전 세계적으로 비만의 문제점이 드러남에 따라 국가적 차원에서 비만인구를 줄이기 위한 노력을 하고 있다. 비만 해소에 가장 효율적인 운동으로 평가받고 있는 걷기운동을 효율적이고 효과적으로 수행할 수 있도록 도와주는 만보기는 다양한 형태의 기기 또는 어플리케이션으로 큰 인기를 얻고 있다. 이에 본 논문에서는 보다 정확한 만보기를 제작하기 위해 센서 및 체형, 신발의 종류에 따라 어떠한 특성을 가지는지 분석하고 효과적인 만보기 어플리케이션 구축 방법을 제안한다.