• Bulletin of the Korean Chemical Society
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• v.14 no.6
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• pp.678-681
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• 1993

The new ternary phase $UP_2S_6$ has been prepared and structurally characterized. The compound is isostructural with $ZrP_2S_6$ and $ThP_2S_6$ but is different from $TiP_2S_6$. The structure has been determined by a single crystal X-ray diffraction technique. $UP_2S_6$ crystallizes in the the tetragonal system $({C^2}_{4h}-P4_2/m,\;a=6.797(7)\;{\AA},\;c=9.738(12)\;{\AA})$ with two formula units in the unit cell. The structure can be described in terms of $U^{4+}$ and ${P_2S_6}^{4-}$ ions. This hexathiohypodiphosphate anion $({P_2S_6}^{4-})$ has ideally staggered conformation. The $U^{4+}$ cation is coordinated by 8 sulfur atoms in a slightly distorted dodecahedral geometry (42m). The distribution of sulfur atoms is very well optimized for this geometry.

• Bulletin of the Korean Chemical Society
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• v.30 no.12
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• pp.3011-3015
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• 2009

Structural and thermo-analytical studies were carried out to understand the phase formation kinetics of the single phase $Bi_5Ti_3FeO_{15}$ (BTFO) nanocrystals in $Bi_2O_3-Fe_2O_3-TiO_2$, during the polymerized complex (PC) synthesis method. The crystallization of Aurivillius phase $Bi_5Ti_3FeO_{15}$ layered perovskite was found to be initiated and achieved under the temperature conditions in the range of ${\sim}$800 to 1050$^{\circ}C$. The activation energy for grain growth of $Bi_5Ti_3FeO_{15}$ nanocrystals (NCs) was very low in case of NCs formed by PC (2.61 kJ/mol) than that formed by the solid state reaction (SSR) method (10.9 kJ/mol). The energy involved in the phase transformation of Aurivillius phase $Bi_5Ti_3FeO_{15}$ from $Bi_2O_3-Fe_2O_3-TiO_2$ system was ${\sim}$ 69.8 kJ/mol. The formation kinetics study of $Bi_5Ti_3FeO_{15}$ synthesized by SSR and PC methods would not only render a large impact in the nanocrystalline material development but also in achieving highly efficient visible photocatalysts.

• Transactions of the Korean hydrogen and new energy society
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• v.18 no.3
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• pp.325-333
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• 2007

[ $LiNi_{0.995}Al_{0.005}O_2$ ], $LiNi_{0.990}Ti_{0.010}O_2$ and $LiNi_{0.0990}Al_{0.005}Ti_{0.005}O_2$ were synthesized with a combustion method by calcining in an $O_2$ stream at $750^{\circ}C$ for 36 h. The X-ray diffraction patterns of these synthesized samples showed $-NaFeO_2$ structure of rhombohedral system(space group; $R{\bar{3}}\;m$) with no evidence of impurities. Among these samples, $LiNi_{0.995}Al_{0.005}O_2$ exhibited comparatively high first discharge capacity and discharge capacity, and the best cycling performance. $LiNi_{0.995}Al_{0.005}O_2$ had the first discharge capacity of 165.2 mA h/g and a discharge capacity of 116.7 mA h/g at the 50th cycle at 0.1C rate. It showed the first discharge capacity of 141.0 mA h/g and a discharge capacity of 93.5 mA h/g at the 50th cycle at 0.5C rate.

• Applied Chemistry for Engineering
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• v.8 no.3
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• pp.410-415
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• 1997

Fibrious potassium hexatitanate whisker was produced from the calcination process using a mixture of the natural rutile ore and industrial $K_2CO_3$. Fibrous Potassium titanate was prepared by the following procedures the starting material consisting of $K_2O{\cdot}4.4TiO_2$ was calcined at $1050^{\circ}C$ for 3 hrs. The calcined products obtained under the above condition consisted mainly of potassium hexatitanate with a small admixture of potassium dititanate and potassium tetratitanate. Therefore the single phase of potassium hexatitanate was obtained by heat treatment of $850^{\circ}C$, 3 hrs.

• Applied Chemistry for Engineering
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• v.20 no.3
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• pp.329-334
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• 2009

Yttrium ions doped $TiO_2$ particles have been prepared using a low temperature combustion method. The physical properties were investigated, together with the activity of $TiO_2$ particles as a photocatalyst for the decomposition of methylene blue. From XRD results, the major phase of all the $TiO_2$ particles prepared under basic condition was an anatase structure but a rutile peak was observed when they are prepared under acidic condition. The crystallite size of $TiO_2$ particles was decreased as the molar ratio of CA/TTIP increased. The photocatalytic activity increased with an increase of CA/TTIP molar ratio and pH in the solution. In addition, the doping of 1.0 mole% yttrium ion on the $TiO_2$ enhanced the photocatalytic activity and showed the higher activity than commercial P-25 catalyst.

• Journal of Photoscience
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• v.1 no.1
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• pp.31-37
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• 1994

Photoirradiation at > 300 nm onto a suspension of platinized TiO$_2$ (TiO$_2$-Pt) particles in an aqueous solution. of N$_{\varepsilon}$-carbamyI-L-lysine (Lys(CONH)$_2$) induced the selective N-cyclization of Lys(CONH$_2$) into almost optically pure L-pipecolinic acid (PCA) under argon atmosphere at ambient temperature. Among various TiO$_2$-Pt catalysts, a P-25 (Degussa) powder platinized via impregnation from chloroplatinic acid followed by hydrogen reduction at 753 K exhibited the highest photocatalytic activity for Lys(CONH$_2$) consumption and L-PCA production. GC-MS analyses of L-PCA obtained photocatalytically from $^{15}$N$\alpha$-Lys(CONH$_2$) revealed the selective formation $^{15}$N-substituted L-PCA. This implies that the mechanism for L-PCA production contains selective cleavage of C$_{\varepsilon}$-N bond and intramolecular alkylation at $\alpha$-amino group. Effect of pH on the rate of this photocatalytic reaction was investigated in detail and compared with the pH-dependent charge distribution in Lys(CONH$_2$) molecule. It is clarified that protonation-deprotonation of $\alpha$-amino group gives marked influence on the rate and selectivity of the photocatalytic reaction. On the basis of these results, it is concluded that the selective production of optically pure L-PCA, especially in an acidic suspension of TiO$_2$-Pt, was attributed to the enhanced protonation of $\alpha$-amino group to prevent undesirable oxidation by photogenerated positive holes and blocking of $\varepsilon$-amino group to yield racemic Schiff base intermediate.

• Korean Journal of Materials Research
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• v.30 no.1
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• pp.14-21
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• 2020

Carbon supports for dispersed platinum (Pt) electrocatalysts in direct methanol fuel cells (DMFCs) are being continuously developed to improve electrochemical performance and catalyst stability. However, carbon supports still require solutions to reduce costs and improve catalyst efficiency. In this study, we prepare well-dispersed Pt electrocatalysts by introducing titanium dioxide (TiO₂) into biomass based nitrogen-doped carbon supports. In order to obtain optimized electrochemical performance, different amounts of TiO₂ component are controlled by three types (Pt/TNC-2 wt%, Pt/TNC-4 wt%, and Pt/TNC-6 wt%). Especially, the anodic current density of Pt/TNC-4 wt% is 707.0 mA g^-1_pt, which is about 1.65 times higher than that of commercial Pt/C (429.1 mA g^-1_pt); Pt/TNC-4wt% also exhibits excellent catalytic stability, with a retention rate of 91 %. This novel support provides electrochemical performance improvement including several advantages of improved anodic current density and catalyst stability due to the well-dispersed Pt nanoparticles on the support by the introduction of TiO₂ component and nitrogen doping in carbon. Therefore, Pt/TNC-4 wt% may be electrocatalyst a promising catalyst as an anode for high-performance DMFCs.

• Applied Chemistry for Engineering
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• v.8 no.2
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• pp.292-300
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• 1997

In this study PZT powders were prepared with shapes of cubic by hydrothermal synthesis with various starting materials, and the sintering characteristics of the powders were investigated. The particle shapes were cubic regardless of starting materials, but the mean size of particles formed using $Pb(NO_3)_2$, $Ti(OC_4H_9)_4$ and $Zr(OC_4H_9)_4$ was relatively smaller than that of particles prepared from other starting materials. Agitation of the feedstock during hydrothermal reaction results in decreasing the required reaction temperature for the formation of nuclei, and in increasing the size of product particles. XRD results showed that the major phase of PZT crystal powders was a tetragonal phase at the Zr to Ti ratio of 40 to 60, or a rhombohedral phase at its ratio of 60 to 40. The density of a sintered body made from the hydrothermal powders in PbO surrounding varied with sintering temperatures and with periods of sintering time. The experimental results also showed that the optimum sintering condition was at $1150^{\circ}C$ for a 2hr sintering, and that the density of a sintered body was $7.6g/cm^3$.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.3
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• pp.247-254
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• 2014

The synthesis of Fischer-Tropsch oil is the catalytic hydrogenation of CO to give a range of products, which can be used for the production of high-quality diesel fuel, gasoline and linear chemicals. Our cobalt based catalyst was prepared Co/alumina, silica and titania by the incipient wet impregnation of the nitrates of cobalt and promoter with supports. Cobalt catalysts was calcined at $350^{\circ}C$ before being loaded into the FT reactors. After the reduction of catalyst has been carried out under $450^{\circ}C$ for 24hrs, FT reaction of the catalyst has been carried out at GHSV of 4,000/hr under $200^{\circ}C$ and 20atm. From these test results, we have obtained the results as following ; in case of 12wt% Co-supported $Al_2O_3$, $SiO_2$ and $TiO_2$ catalysts, maximum activities of the catalysts were appeared at the promoters of Mn, Mo and Ce respectively. The activity of 12wt% $Co/Al_2O_3$ added a Mn promoter was about 3 times as high as that of 12wt% $Co/Al_2O_3$ catalyst without promoters. When it has been the experiment at the range of reaction temperature of $200{\sim}220^{\circ}C$ and GHSV of 1,546~5,000/hr, the results have shown generally increasing the activities with the increase of reaction temperature and GHSV.

• Bulletin of the Korean Chemical Society
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• v.30 no.3
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• pp.630-635
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• 2009

For use as a photocatalyst, bismuth tungsten oxide, $Bi_2WO_6$, was successfully synthesized by hydrothermal treatment at pH = 11 and heating at 200 ${^{\circ}C}$ for 24h, and samples were subsequently thermal treated at 400, 600, and 800 ${^{\circ}C}$ to increase crystallinity. TEM results revealed that the initial untreated particles were sheet‐shaped, grain size was below 80 nm, and it increased with treated temperatures. These $Bi_2WO_6$ samples absorbed at around 400 nm in the visible light range and the intensity of absorption was particularly strongest in samples thermal treated at 600 ${^{\circ}C}$. Their photoluminescence abilities, related to the recombination between the excited electrons and holes, were overall small for other general photocatalysts such as TiO2, and the smallest in the case of thermal treatment at 600 ${^{\circ}C}$, as reversible result of UV‐visible absorbance. Methyl orange of 5.0 ppm aqueous solution was almost completely removed after 2 h when treated over the $Bi_2WO_6$ thermal treated at 600 ${^{\circ}C}$.