Highly Fluorescent and Stable Quantum Dot-Polymer-Layered Double Hydroxide Composites

Cho, Seungho,Kwag, Jungheon,Jeong, Sanghwa,Baek, Yeonggyeong,Kim, Sungjee American Chemical Society 2013 Chemistry of materials Vol.25 No.7

<P>We report a designed strategy for a synthesis of highly luminescent and photostable composites by incorporating quantum dots (QDs) into layered double hydroxide (LDH) matrices without deterioration of a photoluminescence (PL) efficiency of the fluorophores during the entire processes of composite formations. The QDs synthesized in an organic solvent are encapsulated by polymers, poly(maleic acid-alt-octadecene) to transfer them into water without altering the initial surface ligands. The polymer-encapsulated QDs with negative zeta potentials (−29.5 ± 2.2 mV) were electrostatically assembled with positively charged (24.9 ± 0.6 mV) LDH nanosheets to form QD-polymer-LDH composites (PL quantum yield: 74.1%). QD-polymer-LDH composite films are fabricated by a drop-casting of the solution on substrates. The PL properties of the films preserve those of the organic QD solutions. We also demonstrate that the formation of the QD-polymer-LDH composites affords enhanced photostabilities through multiple protections of QD surface by polymers and LDH nanosheets from the environment.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2013/cmatex.2013.25.issue-7/cm3040505/production/images/medium/cm-2012-040505_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm3040505'>ACS Electronic Supporting Info</A></P>

Strategy for Synthesizing Quantum Dot-Layered Double Hydroxide Nanocomposites and Their Enhanced Photoluminescence and Photostability

Cho, Seungho,Jung, Sungwook,Jeong, Sanghwa,Bang, Jiwon,Park, Joonhyuck,Park, Youngrong,Kim, Sungjee American Chemical Society 2013 Langmuir Vol.29 No.1

<P>Layered double hydroxide-quantum dot (LDH-QD) composites are synthesized via a room temperature LDH formation reaction in the presence of QDs. InP/ZnS (core/shell) QD, a heavy metal free QD, is used as a model constituent. Interactions between QDs (with negative zeta potentials), decorated with dihydrolipoic acids, and inherently positively charged metal hydroxide layers of LDH during the LDH formations are induced to form the LDH-QD composites. The formation of the LDH-QD composites affords significantly enhanced photoluminescence quantum yields and thermal- and photostabilities compared to their QD counterparts. In addition, the fluorescence from the solid LDH-QD composite preserved the initial optical properties of the QD colloid solution without noticeable deteriorations such as red-shift or deep trap emission. Based on their advantageous optical properties, we also demonstrate the pseudo white light emitting diode, down-converted by the LDH-QD composites.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2013/langd5.2013.29.issue-1/la303812y/production/images/medium/la-2012-03812y_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la303812y'>ACS Electronic Supporting Info</A></P>

Porous ZnO-ZnSe nanocomposites for visible light photocatalysis.

Cho, Seungho,Jang, Ji-Wook,Lee, Jae Sung,Lee, Kun-Hong RSC Pub 2012 Nanoscale Vol.4 No.6

<P>We report the synthesis of porous ZnO-ZnSe nanocomposites for use in visible light photocatalysis. Porous ZnO nanostructures were synthesized by a microwave-assisted hydrothermal reaction then converted into porous ZnO-ZnSe nanocomposites by a microwave-assisted dissolution-recrystallization process using an aqueous solution containing selenium ions. ZnO and ZnSe nanocrystallites of the nanocomposites were well-mixed (rather than forming simple core-shell (ZnO-ZnSe) structures), particularly, in the outer regions. Both ZnO and ZnSe were present at the surface and exposed to the environment. The porous ZnO-ZnSe nanocomposites showed absorption bands in the visible region as well as in the UV region. The porous ZnO-ZnSe nanocomposites had much higher activities than the porous ZnO nanostructures. Control experiments using cutoff filters revealed that the main photocatalytic activity of the synthesized nanostructures arose from photo-excitation of the semiconductor (ZnO or ZnSe) via absorption of light of an energy equal to or exceeding the band gap energy.</P>

Formation of quasi-single crystalline porous ZnO nanostructures with a single large cavity

Cho, Seungho,Kim, Semi,Jung, Dae-Won,Lee, Kun-Hong Royal Society of Chemistry 2011 Nanoscale Vol.3 No.9

<P>We report a method for synthesizing quasi-single crystalline porous ZnO nanostructures containing a single large cavity. The microwave-assisted route consists of a short (about 2 min) temperature ramping stage (from room temperature to 120 °C) and a stage in which the temperature is maintained at 120 °C for 2 h. The structures produced by this route were 200–480 nm in diameter. The morphological yields of this method were very high. The temperature- and time-dependent evolution of the synthesized powders and the effects of an additive, vitamin C, were studied. Spherical amorphous/polycrystalline structures (70–170 nm in diameter), which appeared transitorily, may play a key role in the formation of the single crystalline porous hollow ZnO nanostructures. Studies and characterization of the nanostructures suggested a possible mechanism for formation of the quasi-single crystalline porous ZnO nanostructures with an interior space.</P> <P>Graphic Abstract</P><P>We report a method for synthesizing single crystalline porous ZnO nanostructures containing a single large cavity. Transitory spherical amorphous/polycrystalline particles may play a key role in the formation of these nanostructures. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1nr10609k'> </P>

An exceptionally facile method to produce layered double hydroxides on a conducting substrate and their application for solar water splitting without an external bias

Cho, Seungho,Jang, Ji-Wook,Park, Yoon Bin,Kim, Jae Young,Magesh, Ganesan,Kim, Jin Hyun,Seol, Minsu,Yong, Kijung,Lee, Kun-Hong,Lee, Jae Sung The Royal Society of Chemistry 2014 ENERGY AND ENVIRONMENTAL SCIENCE Vol.7 No.7

<P>An exceptionally facile process is presented for <I>in situ</I> formation of zinc chromium layered double hydroxide (ZnCr:LDH) nanosheets on a conducting substrate. Thus, ZnCr:LDH nanosheets were synthesized from a metallic Zn film/fluorine-doped tin oxide (FTO) glass by simply dipping into a Cr nitrate solution for only one minute at room temperature. Then, ZnCr:LDHs were converted into zinc chromium mixed metal oxide (ZnCr:MMO) nanoparticles by calcination. Under visible light irradiation (<I>λ</I> > 420 nm), the <I>in situ</I> synthesized ZnCr:MMO photoanode exhibited a stable and an order-of-magnitude higher activity for photoelectrochemical water splitting than that of a ZnCr:MMO film fabricated <I>ex situ</I> by electrophoretic deposition of already-synthesized ZnCr:MMO powders. More significant was that it generated anodic photocurrents even without an externally applied bias potential, which is an unprecedented result for an oxide photoanode-driven PEC system working under visible light.</P> <P>Graphic Abstract</P><P>A photoanode derived from layered double hydroxide is applied for bias-free solar water splitting. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3ee43965h'> </P>

Three-Dimensional Type II ZnO/ZnSe Heterostructures and Their Visible Light Photocatalytic Activities

Cho, Seungho,Jang, Ji-Wook,Kim, Jungwon,Lee, Jae Sung,Choi, Wonyong,Lee, Kun-Hong American Chemical Society 2011 Langmuir Vol.27 No.16

<P>We report a method for synthesizing three distinct type II 3D ZnO/ZnSe heterostructures through simple solution-based surface modification reactions in which polycrystalline ZnSe nanoparticles formed on the surfaces of single-crystalline ZnO building blocks of 3D superstructures. The experimental results suggested a possible formation mechanism for these heterostructures. The formation of the ZnO/ZnSe heterostructures was assumed to result from a dissolution–recrystallization mechanism. The optical properties of the 3D ZnO/ZnSe heterostructures were probed by UV–vis diffuse reflectance spectroscopy. The 3D ZnO/ZnSe heterostructures exhibited absorption in the visible spectral region. The visible photocatalytic activities of 3D ZnO/ZnSe heterostructures were much higher than those of the 3D pure ZnO structures. The activities of the 3D ZnO/ZnSe heterostructures varied according to the structures under visible light. The morphologies and exposed crystal faces of pure ZnO building blocks prior to surface modification had a significant effect on the visible light photocatalytic processes of ZnO/ZnSe heterostructures after surface modification.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2011/langd5.2011.27.issue-16/la201755w/production/images/medium/la-2011-01755w_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la201755w'>ACS Electronic Supporting Info</A></P>

Solution-based fabrication of ZnO/ZnSe heterostructure nanowire arrays for solar energy conversion

Cho, Seungho,Jang, Ji-Wook,Lim, Sang-Hoon,Kang, Hyun Joon,Rhee, Shi-Woo,Lee, Jae Sung,Lee, Kun-Hong Royal Society of Chemistry 2011 Journal of materials chemistry Vol.21 No.44

<P>We report a method for synthesizing ZnO/ZnSe heterostructure nanowire arrays for use in photoelectrochemical (PEC) water splitting. The surfaces of ZnO nanowires immobilized on a conducting glass substrate were modified to form ZnO/ZnSe heterostructure nanowire arrays through a reaction with an aqueous sodium selenite and hydrazine solution. ZnO/ZnSe heterostructure nanowires with different morphologies were synthesized by varying solution concentrations and reaction times. The ZnO nanowire/ZnSe nanoparticle heterostructures (ZS1) were synthesized by a dissolution–recrystallization mechanism. At longer reaction times and higher solution concentrations, the nanostructure arrays transformed into ZnO nanowire/ZnSe nanosphere heterostructure arrays (ZS2) <I>via</I> Ostwald ripening. ZnO/ZnSe heterostructure arrays (ZS1 and ZS2) yielded higher photocurrents than the pristine ZnO nanowire arrays in a PEC water splitting test under AM 1.5G simulated solar light. The ZnO/ZnSe heterostructure array photoanodes exhibited absorption in the visible spectrum (<550 nm in wavelength) with a high incident-photon-to-current-conversion efficiency (IPCE) of up to 47% (ZS1) or 57% (ZS2) at 0.0 V <I>vs.</I> Ag/AgCl. The photoanode yielded a relatively high photocurrent density of 1.67 mA cm<SUP>−2</SUP> (ZS1) or 2.35 mA cm<SUP>−2</SUP> (ZS2) at 0.3 V compared to the ZnO nanowire arrays (0.125 mA cm<SUP>−2</SUP>). Structural differences between ZS1 and ZS2 yielded different PEC performances. A comparison to ZS2 revealed that ZS1 exhibited a higher photocurrent density under a low applied potential (from −0.78 V to −0.07 V) and a lower photocurrent density under a high applied potential (above −0.07 V).</P> <P>Graphic Abstract</P><P>Through a simple surface modification reaction, ZnO/ZnSe heterostructure nanowire arrays were fabricated for use in photoelectrochemical water splitting. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1jm14014k'> </P>

Quantum dot-layered double hydroxide composites for near-infrared emitting codes

Cho, Seungho,Hong, Seong Cheol,Kim, Sungjee The Royal Society of Chemistry 2014 Journal of Materials Chemistry C Vol.2 No.3

Linux-based Real Time Monitoring System of Mobile Robots

SeungHo Cho,I. O. Lee,JangMyung Lee 제어로봇시스템학회 2006 제어로봇시스템학회 국제학술대회 논문집 Vol.2006 No.10

The Difference between News Coverage and News Release of Political Parties During A Political Crisis

SeungHo Cho(조승호) 한국콘텐츠학회 2018 한국콘텐츠학회논문지 Vol.18 No.11

본 연구의 목적은 정치적 위기 상황에서 위기대응에 대한 언론보도와 정당의 차이를 조사하는 것이다. 과거 정치적 사례를 통해 정치적 상황, 정치적 집단의 위기대응, 언론보도를 살펴보았다. 본 연구가 살펴본 사례는 16대 대통령 선거운동에서 불법 선거자금 모금과 관련해서 두 정당(새천년민주당 vs. 한나라당)의 대응이다. 두 정당은 그들의 이미지 회복을 위한 위기대응 전략을 활용하였다. 본 연구는 위기대응메시지와 언론보도 메시지의 차이를 내용분석을 통해서 살펴보았다. 그 결과 특정 정당의 위기대응 메시지와 뉴스미디어는 차이를 보이지 않았으나, 다른 정당의 경우는 차이가 나타났다. 이러한 뉴스보도와 정당의 메시지 일치 여부는 공중의 위기평가에 중요한 영향을 미친다. 본 연구는 위기커뮤니케이션에서 조직의 위기대응 메시지와 뉴스미디어의 보도 차이의 중요성을 다뤘다는 점에서 의의를 갖는다. The purpose of this study is to explore a difference in crisis between media and parties. This research examined political crisis situation, crisis response, and media coverage using a case. Two main political parties in Korean faced the illegal fund raising case during the 16th presidential election. They used types of crisis response strategies for restoring or maintaining their reputation. This study found that a party’s crisis response was consistent with news media, but another party’s message was significantly different from news media. Such match or mismatch between a party and news media will influence on public evaluation toward a crisis response. This study has meaningful contribution in that the difference between an organizational crisis response message and news media coverage is significant.