Solvent Coordination Strength: An Essential Factor for Metal Catalytic Reactions

Nak Cheon Jeong(정낙천) 한국고분자학회 2023 한국고분자학회 학술대회 연구논문 초록집 Vol.48 No.1

New Insights into ETS-10 and Titanate Quantum Wire: A Comprehensive Characterization

Jeong, Nak Cheon,Lee, Young Ju,Park, Jung-Hyun,Lim, Hyunjin,Shin, Chae-Ho,Cheong, Hyeonsik,Yoon, Kyung Byung American Chemical Society 2009 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.131 No.36

<P>The titanate quantum wires in ETS-10 crystals remain intact during ion exchange of the pristine cations (Na(+)(0.47) + K(+)(0.53)) with M(n+) ions (M(n+) = Na(+), K(+), Mg(2+), Ca(2+), Sr(2+), Ba(2+), Pb(2+), Cd(2+), Zn(2+)) and during reverse exchange of the newly exchanged cations with Na(+). The binding energies of O(1s) and Ti(2p) decrease as the electronegativity of the cation decreases, and they are inversely proportional to the negative partial charge of the framework oxygen [-delta(O(f))]. At least five different oxygen species were identified, and their binding energies (526.1-531.9 eV) indicate that the titanate-forming oxides are much more basic than those of aluminosilicate zeolites (530.2-533.3 eV), which explains the vulnerability of the quantum wire to acids and oxidants. The chemical shifts of the five NMR-spectroscopically nonequivalent Si sites, delta(I(A)), delta(I(B)), delta(II(A)), delta(II(B)), and delta(III), shift downfield as -delta(O(f)) increases, with slopes of 2.5, 18.6, 133.5, 216.3, and 93.8 ppm/[-delta(O(f))], respectively. The nonuniform responses of the chemical shifts to -delta(O(f)) arise from the phenomenon that the cations in the 12-membered-ring channels shift to the interiors of the cages surrounded by four seven-membered-ring windows. On the basis of the above, we assign delta(I(A)), delta(I(B)), delta(II(A)), and delta(II(B)) to the chemical shifts arising from Si(12,12), Si(12,7), Si(7,12), and Si(7,7) atoms, respectively. The frequency of the longitudinal stretching vibration of the titanate quantum wire increases linearly and the bandwidth decreases nonlinearly with increasing -delta(O(f)), indicating that the titanate quantum wire resembles a metallic carbon nanotube. As the degree of hydration increases, the vibrational frequency shifts linearly to higher frequencies while the bandwidth decreases. We identified another normal mode of vibration of the quantum wire, which vibrates in the region of 274-280 cm(-1). In the dehydrated state, the band-gap energy and the first absorption maximum shift to lower energies as -delta(O(f)) increases, indicating the oxide-to-titanium(IV) charge-transfer nature of the transitions.</P>

Length-Dependent Band-Gap Shift of TiO₃²⁻ Molecular Wires Embedded in Zeolite ETS-10

Jeong, Nak ,Cheon,Lee, Myoung ,Hee,Yoon, Kyung ,Byung WILEY-VCH Verlag 2007 Angewandte Chemie Vol.46 No.31

<B>Graphic Abstract</B> <P>Mind the gap! The titanosilicate zeolite ETS-10 contains TiO<SUB>3</SUB><SUP>2−</SUP> molecular wires (see picture). A reliable method has been developed to synthesize high-quality ETS-10 crystals of various sizes. Measurements on the crystals allow the dependence of the band-gap energy on the length of the TiO<SUB>3</SUB><SUP>2−</SUP> wires to be elucidated. <img src='wiley_img/14337851-2007-46-31-ANIE200701676-content.gif' alt='wiley_img/14337851-2007-46-31-ANIE200701676-content'> </P>

학습지 기반의 언플러그드 활동 프로그램에 따른 초등학교 3,4학년 학생의 컴퓨팅 사고력의 변화 차이

성락규(Nak-Gyu Seong),김의정(Eui-Jeong Kim),정종인(Jong-In Chung),김창석(Chang Suk Kim),강신천(Shin-Cheon Kang) 한국정보통신학회 2021 한국정보통신학회 종합학술대회 논문집 Vol.25 No.2

본 연구에서는 학습지 기반의 언플러그드 활동 프로그램이 초등학교 3,4학년 학생들의 컴퓨팅 사고력 향상에 미치는 효과를 통계적으로 분석해보았다. 연구는 충청남도 소재 G초등학교 3,4학년 18명을 대상으로 진행되었으며 컴퓨팅 사고력 검사를 사전에 실시한 후 학습지 기반의 언플러그드 프로그램을 실험집단 9명에게 총 6차시로 구성하여 진행하였다. 이후 사후 검사를 실시하여 컴퓨팅 사고력의 향상 정도를 분석하였다. 분석 결과, 학습지 기반의 언플러그드 프로그램이 초등학교 3,4학년 학생들의 컴퓨팅 사고력이 향상되었고 긍정적인 효과를 미치는 것으로 확인되었다. In this study, the effect of the workbook-based unplugged activity program on the improvement of computational thinking skills of elementary school students in 3rd and 4th grade was statistically analyzed. The study was conducted with 18 students in the 3rd and 4th grades of G Elementary School located in Chungcheongnam-do, and after conducting a computational thinking ability test in advance, an unplugged program based on the workbook was conducted in a total of 6 sessions with 9 members of the experimental group. After that, a post-mortem examination was conducted to analyze the degree of improvement in computational thinking ability. As a result of the analysis, it was confirmed that the workbook-based unplugged program improved the computational thinking skills of elementary school students in 3rd and 4th grade and had a positive effect.

블루베리 식초제조와 품질특성

김낙구(Nak-Ku Kim),하기정(Gi-Jeong Ha),조숙현(Sook-Hyun Cho),천미건(Mi-Geon Cheon),강남대(Nam-Dae Kang),손길만(Gil-Man Shon),노치웅(Chi-Woong Rho) 한국원예학회 2009 한국원예학회 학술발표요지 Vol.2009 No.5

Core–shell strain structure of zeolite microcrystals

Cha, Wonsuk,Jeong, Nak Cheon,Song, Sanghoon,Park, Hyun-jun,Thanh Pham, Tung Cao,Harder, Ross,Lim, Bobae,Xiong, Gang,Ahn, Docheon,McNulty, Ian,Kim, Jungho,Yoon, Kyung Byung,Robinson, Ian K.,Kim, Hyunju Nature Publishing Group 2013 Nature materials Vol.12 No.8

Zeolites are crystalline aluminosilicate minerals featuring a network of 0.3–1.5-nm-wide pores, used in industry as catalysts for hydrocarbon interconversion, ion exchangers, molecular sieves and adsorbents. For improved applications, it is highly useful to study the distribution of internal local strains because they sensitively affect the rates of adsorption and diffusion of guest molecules within zeolites. Here, we report the observation of an unusual triangular deformation field distribution in ZSM-5 zeolites by coherent X-ray diffraction imaging, showing the presence of a strain within the crystal arising from the heterogeneous core–shell structure, which is supported by finite element model calculation and confirmed by fluorescence measurement. The shell is composed of H-ZSM-5 with intrinsic negative thermal expansion whereas the core exhibits a different thermal expansion behaviour due to the presence of organic template residues, which usually remain when the starting materials are insufficiently calcined. Engineering such strain effects could have a major impact on the design of future catalysts.

Photovoltaic Effects of CdS and PbS Quantum Dots Encapsulated in Zeolite Y

Kim, Hyun Sung,Jeong, Nak Cheon,Yoon, Kyung Byung American Chemical Society 2011 Langmuir Vol.27 No.23

<P>Zeolite Y films (0.35–2.5 μm), into which CdS and PbS quantum dots (QDs) were loaded, were grown on ITO glass. The CdS QD-loaded zeolite Y films showed a photovoltaic effect in the electrolyte solution consisting of Na<SUB>2</SUB>S (1 M) and NaOH (0.1 M) with Pt-coated F-doped tin oxide glass as the counter electrode. In contrast, the PbS QD-loaded zeolite Y films exhibited a negligible PV effect. This contrasting behavior was proposed to arise from the large difference in driving force for the electron transfer from S<SUP>2–</SUP> in the solution to the hole in the valence band of QDs, with the former being much larger (∼2 eV) than the latter (∼1 eV). In the case of CdS QD-loaded zeolite Y with a loaded amount of CdS of 6.3 per unit cell, the short circuit current, open circuit voltage, fill factor, and efficiency were 0.3 mA cm<SUP>–2</SUP>, 423 V, 28, and 0.1%, respectively, under the AM 1.5, 100 mW cm<SUP>–2</SUP> condition. This cell was stable for more than 18 days of continuous measurements. A large (3-fold) increase in overall efficiency was observed when PbS QD-loaded zeolite Y on ITO glass was used as the counter electrode. This phenomenon suggests that the uphill electron transfer from ITO glass to S in the solution is facilitated by the photoassisted pumping of the potential energy of the electron in ITO glass to the level that is higher than the reduction potential of S by PbS QDs. Under this condition, the incident-photon-to-current conversion efficiency (IPCE) value at 398 nm was 42% and the absorbed-photon-to-current conversion efficiency (APCE) value at 405 nm was 82%. The electrolyte-mediated interdot charge transport within zeolite films is concluded to be responsible for the overall current flow.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2011/langd5.2011.27.issue-23/la2025395/production/images/medium/la-2011-025395_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la2025395'>ACS Electronic Supporting Info</A></P>

Control of mode of crystal networking during monolayer assembly of microcrystals on water.

Park, Jin Seon,Jeong, Nak Cheon,Lee, Yun-Jo,Kim, Min Jung,Yoon, Kyung Byung American Scientific Publishers 2010 Journal of Nanoscience and Nanotechnology Vol.10 No.1

<P>A series of hydrocarbon (HC)-coated cubic zeolite microcrystals (1.7 microm) was prepared. The HCs were n-octyl, n-dodecyl, methyl n-undecanoate, n-octadecyl, and n-heptadecafluorodecyl. The measured water contact angles (theta) of the corresponding HC-coated glass plates were 64, 77, 82, 102, and 105 degrees, respectively, indicating that the hydrophobicity of the surface-tethered hydrophobic chain (HC) increased in the above order. The HC-coated zeolite microcrystals readily formed closely packed monolayers at the air-water interface through interdigitation of surface-tethered HCs, and on glass plates after transferring onto glass plates by dip coating. Interestingly, while the mode of networking was face-to-face (FTF) contacting with n-octyl or n-dodecyl (theta < or =77 degrees) as HC, it changed to edge-to-edge (ETE) contacting mode with n-octadecyl or n-heptadecafluorodecyl (theta > or = 102 degrees) as HC. With methyl n-undecanoate (theta = 82 degrees) as HC, both modes appeared in the monolayers, with about equal populations. The resulting monolayers of cubic zeolite microcrystals with their three-fold axes oriented perpendicular to substrates would be useful for application of the zeolite monolayers for advanced materials.</P>

Metal coordination and metal activation abilities of commonly unreactive chloromethanes toward metal-organic frameworks

Bae, Jinhee,Lee, Eun Ji,Jeong, Nak Cheon The Royal Society of Chemistry 2018 Chemical communications Vol.54 No.50

<P>Over the last two decades, metal-organic frameworks (MOFs) have received particular attention because of their attractive properties such as permanent nanoporosity and the extraordinary functionality of open coordination sites (OCSs) at metal nodes. In particular, MOFs with open-state OCSs have shown potential in applications such as chemical separation, molecular sorption, catalysis, ionic conduction, and sensing. Thus, the activation of OCSs, <I>i.e.</I>, the removal of coordinated solvent to produce open-state OCSs, has been viewed as an essential step that must be performed prior to the use of the MOFs in the aforementioned applications. This Feature Article focuses on the chemical functions of the commonly unreactive chloromethanes, <I>i.e.</I>, dichloromethane (DCM) and trichloromethane (TCM), including their coordination to OCSs and activation of OCSs. Treatment with a chloromethane is a chemical route to activate OCSs that does not require an additional supply of external thermal energy. Importantly, a plausible mechanism for the chemical process, in which DCM and TCM weakly coordinate to the OCSs and then spontaneously dissociate in an intermediate step, which is proposed based on the results obtained from Raman studies will be discussed. Possible applications of chloromethane treatment to activate large-area MOF films and MOF-polymer mixed matrices, which can be propagated in molecular capture, will also be described.</P>

Porphyrin sensitized solar cells: TiO₂ sensitization with a π-extended porphyrin possessing two anchoring groups

Lee, Chang Yeon,She, Chunxing,Jeong, Nak Cheon,Hupp, Joseph T. Royal Society of Chemistry 2010 Chemical communications Vol.46 No.33

<P>A π-extended porphyrin possessing two anchoring groups has been synthesized and successfully applied to dye-sensitized solar cells with a power conversion efficiency of 5.5%, rendering it comparable to the performance of N719-sensitized solar cells under the conditions employed here.</P> <P>Graphic Abstract</P><P>A π-extended porphyrin possessing two anchoring groups has been synthesized and successfully applied to dye-sensitized solar cells with a power conversion efficiency of 5.5%. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0cc00257g'> </P>