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Lee, Juheon,Park, Yohan,Joo, Sang Woo,Sohn, Youngku Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.11
Eu(III)-doped $CeO_2$ nanorods were prepared by a co-precipitation method at room temperature, and their photoluminescence profiles were examined with different Eu(III)-doping concentrations and thermal annealing temperatures. Scanning electron microscopy, X-ray diffraction crystallography and UV-Vis absorption spectroscopy were employed to examine the morphology, crystal structure and photon absorption profiles of the nanorods, respectively. Additionally, their 2D and 3D-photoluminescence profile maps were obtained to fully understand the photoluminescence mechanism. We found that the magnetic dipole $^5D_0{\rightarrow}^7F_1$ and the electric dipole $^5D_0{\rightarrow}^7F_2$ transitions of Eu(III) were highly dependent on the doping concentration, annealing temperature and excitation wavelength, which was explained by the presence of different Eu(III)-doping sites (with and without an inversion center) in the $CeO_2$ host with a cubic crystal structure.
Synthesis and Characterization of 1-D BiSI and 2-D BiOI Nanostructures
Lee, Juheon,Min, Bong-Ki,Cho, Insu,Sohn, Youngku Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.3
We have prepared 1-D BiSI and 2-D BiOI nanostructures, and characterized them by scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction crystallography, thermogravimetric analysis/differential scanning calorimetry, and UV-visible absorption. Here, we first report clear HR-TEM image of BiSI. In addition, we first found that the growth direction of BiSI is [12-1] plane, with the neighboring distance of 0.30 nm. The crystal structures of BiSI and BiOI are found to be orthorhombic (Pnam) and tetragonal (P4/nmm), respectively. The absorption band gaps of BiSI and BiOI are measured to be 1.55 and 1.92 eV, respectively. Our study could further highlight the applications of V-VI-VII compounds.
Lee, Boreum,Yun, Su-Won,Kim, Sehwa,Heo, Juheon,Kim, Yong-Tae,Lee, Sunggeun,Lim, Hankwon Elsevier 2019 International journal of hydrogen energy Vol.44 No.4
<P><B>Abstract</B></P> <P>Computational fluid dynamics (CFD) studies have been carried out for CO<SUB>2</SUB> reforming of methane in both a packed-bed reactor (PBR) and a membrane reactor (MR) with a heating tube as a heat source at the center of a reactor. The effect of a reactor geometry on the temperature and H<SUB>2</SUB> and CH<SUB>4</SUB> concentration profiles within a PBR and a MR have been investigated numerically by changing the distance of membranes from the center of a heating tube (D<SUB>center</SUB> = radial distance between the center of the reactor and the center of the membrane) for a given heating tube temperature. The distances of the center of the membranes in a MR from the reactor center were 0.028 m, 0.03 m, 0.033 m, 0.035 m, 0.038 m, 0.04 m, 0.042 m, 0.044 m and 0.045 m. With the help of COMSOL Multiphysics<SUP>®</SUP> modeling software, it was possible to visualize temperature and concentration profiles both axially and radially. Interestingly, it was found that H<SUB>2</SUB> enhancement is proportional to both D<SUB>center</SUB> and the magnitude of the H<SUB>2</SUB> flux. Further studies for the effect of a heating tube radius proposed an optimum radius for a maximum H<SUB>2</SUB> yield enhancement in a MR. Consequently, it turned out that CFD studies can be used as a critical guideline for an efficient reactor design focusing on a reactor geometry in a MR for given conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Computational fluid dynamics (CFD) studies for CO<SUB>2</SUB> reforming of methane were performed. </LI> <LI> A 3-D visualization showing the effect of a reactor geometry was presented. </LI> <LI> An optimum heating tube radius for a maximum H<SUB>2</SUB> yield enhancement was identified. </LI> </UL> </P>
Juheon Lee,Yohan Park,주상우,손영구 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.11
Eu(III)-doped CeO2 nanorods were prepared by a co-precipitation method at room temperature, and their photoluminescence profiles were examined with different Eu(III)-doping concentrations and thermal annealing temperatures. Scanning electron microscopy, X-ray diffraction crystallography and UV-Vis absorption spectroscopy were employed to examine the morphology, crystal structure and photon absorption profiles of the nanorods, respectively. Additionally, their 2D and 3D-photoluminescence profile maps were obtained to fully understand the photoluminescence mechanism. We found that the magnetic dipole 5D0 → 7F1 and the electric dipole 5D0 → 7F2 transitions of Eu(III) were highly dependent on the doping concentration, annealing temperature and excitation wavelength, which was explained by the presence of different Eu(III)-doping sites (with and without an inversion center) in the CeO2 host with a cubic crystal structure.