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So-Ram Lee,Youhyuk Kim 대한화학회 2020 Bulletin of the Korean Chemical Society Vol.41 No.12
MoS2 can generate useful molybdenum oxides by thermally reacting with LiF or Ag nanoparticles (NPs). MoS2 easily loses sulfide and reacts with oxygen gas upon heating in air to give orthorhombic molybdenum trioxide, α-MoO3. Morphological changes of α-MoO3 from 500 to 900°C were investigated using X-ray powder diffraction and scanning electron microscope. The strong diffraction peaks of the (020), (040), and (060) planes at 800°C revealed highly anisotropic growth of the oxides with a layered crystal structure. In the presence of LiF, MoS2 reacts with oxygen gas to generate Li2MoO4 and MoO2, depending on the LiF concentration. In the presence of Ag NPs, the thermal reactions of MoS2 at 800 and 900°C give silver molybdates Ag2Mo2O7 and Ag2MoO4, respectively. These results demonstrate that MoS2 is an important precursor for generating useful molybdenum oxides on the surface of inert substrates without requiring sophisticated, expensive equipment.
Han-Na Lee,Youhyuk Kim 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.4
Laponite samples intercalated with Tb^(3+) or Tb^(3+),Ce^(3+) ions were prepared by exchange of Na^+ ions in interlayers with Tb^(3+) or Tb^(3+),Ce^(3+) ions. Strong green and weak blue emissions under vacuum ultraviolet (VUV) excitation (λ =158 nm) were observed due to the ^5D_4→^7F_J and ^5D_3→^7F_J emission lines, respectively. Tb^(3+) ions in an interlayer of laponite mainly existed in ion pairs or clusters, as evidenced by the concentration-dependent luminescence of the Tb^(3+) ions on the relative intensities of the ^5D_3→^7F_J and the ^5D_4→^7FJ emission lines, due to the action of a cross-relaxation process. The addition of Ce^(3+) ions increased the thermal stability of Tb^(3+)intercalated laponite up to 650 ^oC and quenched the ^5D_3→^7F_J emission lines, probably by promoting the formation of Tb^(3+) ion pairs at relatively low Tb^(3+) concentrations.
Kim, Dong Hwan,Kim, Youhyuk The Korea Association of Crystal Growth 2021 韓國結晶成長學會誌 Vol.31 No.2
The reaction of ammonium ferric sulfate with sodium borohydride in laponite sol yields nanoiron colloidal solution. This solution in air forms transparent yellow brown solution. The resulting solution reacts with bidentate chelating ligands. The reaction products are characterized by UV-Vis absorption spectroscopy and X-ray diffraction. All compounds show metal to ligand charge transfer band in the region of 400~650 nm in UV-Vis absorption spectra. This indicates the formation of iron-ligand complex by air oxidation of nanoiron. Also, XRD patterns exhibit that the iron-ligand complex is intercalated in the interlayer of laponite.
[ $LaNbO_4$ ] : X (X = Bi, Eu)형광체의 발광 및 저 전압 음극선 발광 특성
온지원,김유혁,On Ji-Won,Kim Youhyuk 한국결정성장학회 2006 한국결정성장학회지 Vol.16 No.1
희토류계 niobates인 $LaNbO_4$(Ln : Y, La, Gd)는 자체 발광형으로 $NbO^{3-}_4$ 이온의 전하 이동에 의한 넓은 띠의 청색 발광 스펙트럼을 410nm에서 나타낸다. 본 연구에서는 새로운 FED용 청색 및 적색 형광체를 개발하기 위하여 $LaNbO_4$ :X (X = Bi, Eu) 형광체를 합성하였으며, $1250^{\circ}C$에서 2시간 소성한 후 $1400^{\circ}C$에서 1시간 소성하였을 때 최대 발광피크를 얻을 수 있었다. 254nm의 여기하에서 $LaNbO_4$ : Bi는 $420\~450nm$ 영역에서 강한 청색 발광 스펙트럼을 나타내며 첨가된 $Bi^{3+}$ 이온 농도가 $1mol\%$일 때 최대 발광세기를 얻었다 $LaNbO_4$ : Eu의 경우는 첨가된 $Eu^{3+}$ 이온 농도가 $10mol\%$일 때 약 610nm에서 최대 적색 발광 스펙트럼을 나타내고 있다. $Eu^{3+}$ 이온 농도가 $10mol\%$ 이하에서는 $415\~460nm$, $530\~560nm$ 및 $570\~620nm$ 영역에서 피크가 관측되고 있다. 이들 형광체의 음극선 발광특성은 빛 발광 특성과 유사한 경향을 보였다. Rare-earth niobates, ag (Ln = Y, La, Gd) are well-known self-activated phosphors due to charge transfer in $NbO^{3-}_4$ showing a broad and strong emission band in the spectral region around 410 nm. In order to find new blue and red phosphors for FED, $LaNbO_4$ : X (X = Bi, Eu) phosphors are prepared through solid-state reactions at high temperature. The optimum reaction condition for these phosphors to give maximum emission intensity is obtained when it is first fired at $1250^{\circ}C$ for 2 h followed by second firing at $1400^{\circ}C$ for 1 h. Under irradiation at 254 nm, $1mol\%\;Bi^{3+}$ doped $LaNbO_4$ phosphor shows strong blue emission band with a range of $420\~450nm$. Also $10mol\%\;Eu^{3+}$ doped $LaNbO_4$ phosphor shows the maximum emission intensity at about 610 nm. Emission peaks at $415\~460nm$, $530\~560nm$and $570\~620nm$are observed in phosphors below $10mol\%\;Eu^{3+}$ doped $LaNbO_4$. Similar results are obtained in cathodoluminescent property of these phosphors.
Preparation and Characterization of Silver Nanoparticles Embedded in Silica Sol Particles
Byung-Kyu Kang,Dong-Min Son,Youhyuk Kim 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.10
Silver nanoparticles coated with silica can be obtained by the reduction of AgNO_3 with hydrazine in the presence of NaOH-stabilized, active silicic acid (polysilicic acid). The size of the silver nanoparticles and the silica shell thicknesses were affected by varying the hydrazine content, the active silicic acid content and the experimental method (e.g. hydrothermal method). Typically, silver nanoparticles sized around 40 nm were aggregated, connected by silica. The presence of peaks centered around 400 nm in UV-vis spectra corresponds to the surface plasmon resonance of silver nanoparticles. The size of the aggregated silver nanoparticles increased with increasing hydrazine concentration. Under hydrothermal conditions at 150 °C the formation of individual silica particles was observed and the sizes of the silver nanoparticles were reduced. The hydrothermal treatment of silver nanoparticles at 180 °C gives a well-defined Ag@SiO_2 core-shell in aggregated silica sol particles. The absorption band observed at around 412 nm were red-shifted with respect to the uncoated silver nanoparticles (λmax = 399 nm) due to the larger refractive index of silica compared to that of water. The formation of silver nanoparticles coated with silica is confirmed by UV-visible absorption spectra, transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS) data.
개선된 단일상 합성법을 이용한 티올화 나노 금의 합성 및 확인
박지수,김유혁,Park, Jisu,Kim, Youhyuk 대한화학회 2017 대한화학회지 Vol.61 No.4
앞선 연구에서 TP(Thiolate-Protected)-나노은의 합성 시 초기에 형성되는 티올화 은 층간화합물의 형성을 막기 위하여 에탄올에 녹아있는 $NaBH_4$와 티올에 $AgNO_3$를 첨가하는 개선된 단일상 합성법을 보고하였다. 본 연구에서는 이 합성법을 보다 일반화하기 위하여 TP-나노금과 나노백금의 합성에 적용하였다. 합성된 생성물의 나노크기, 형상 및 금속에 부착된 티올의 배열은 UV-vis. 스펙트럼, 투과 전자 현미경 사진, X-선 회절 패턴 및 적외선 분광 스펙트럼을 이용하여 규명 하였다. TP-나노금과 나노백금은 구형 및 타원형의 형태를 하고 있으며 입자크기는 각각 약 3~7 nm와 약 2 nm 이하로 나타나고 있다. 한편 TP-나노금의 표면을 감싸는 옥탄티올 음이온의 메틸렌 사슬 [$-(CH_2)_7-$]의 메틸렌 배향은 trans임을 보여주고 있다. One-phase method to prevent the initial formation of Ag(I) thiolate layered materal from the mixture of $AgNO_3$ and thiols was previously developed to generate TP (Thiolate-Protected)-nanosilver. In this modified method, $AgNO_3$ is added to the mixtures of $NaBH_4$ and thiols in ethanol. This method was so successful that it was applied to synthesize TP-nanogold and nanoplatinum. The synthesis and characterization of these nanoparticles by ultraviolet-visible (UV-vis) absorption spectra, transmission electron microscopy (TEM) pictures, X-ray powder differaction (XRD) patterns and infrared(IR) spectra are described. The results show that colloidal nanoparticles are spherical or oval shape and the mean sizes for TP-nanogold and nanoplatinum are about 3~7 nm and below 2 nm, respectively. The conformation of polymethylene [$-(CH_2)_7-$] sequence in octanethiolate attached to nanogold was elucidated as trans.
Jae-Seok Seo,Dong-Min Son,Hanna Lee,Jeekwang Kim,Youhyuk Kim 대한화학회 2009 Bulletin of the Korean Chemical Society Vol.30 No.11
In borohydride-protected nanosilvers in laponite sol, the silver particles aggregate to form short chains and a dumbbell shape. The 1H NMR measurements in this study represent, to our knowledge, the first observation of proton resonances of borohydride-protected nanosilvers in aqueous solution. Borohydride on nanosilver can be exchanged with 11-mercaptoundecanoic acid (MUA) or trioctylphosphine (TOP). Transmission electron microscopy and UV-Vis spectroscopy data show that the number of aggregated silver nanoparticles decreases upon addition of aforementioned ligands due to the formation of silver MPCs (monolayer-protected clusters). Adsorption of MUA or TOP on nanosilver is confirmed through the observation of broad proton resonances of MPCs in 1H NMR spectra.