• Korean Journal of Materials Research
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• v.31 no.2
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• pp.92-96
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• 2021

We report the growth and enhanced photoelectrochemcial (PEC) water-splitting reactivity of few-layer MoS2 nanosheets on TiO2 nanowires. TiO2 nanowires with lengths of ~1.5 ~ 2.0 ㎛ and widths of ~50~300 nm are synthesized on fluorine-doped tin oxide substrates at 180 ℃ using hydrothermal methods with Ti(C4H9O)4. Few-layer MoS2 nanosheets with heights of ~250 ~ 300 nm are vertically grown on TiO2 nanowires at a moderate growth temperature of 300 ℃ using metalorganic chemical vapor deposition. The MoS2 nanosheets on TiO2 nanowires exhibit typical Raman and ultraviolet-visible light absorption spectra corresponding to few-layer thick MoS2. The PEC performance of the MoS2 nanosheet/TiO2 nanowire heterostructure is superior to that of bare TiO2 nanowires. MoS2/TiO2 heterostructure shows three times higher photocurrent than that of bare TiO2 nanowires at 0.6 V. The enhanced PEC photocurrent is attributed to improved light absorption of MoS2 nanosheets and efficient charge separation through the heterojunction. The photoelectrode of the MoS2/TiO2 heterostructure is stably sustained during on-off switching PEC cycle.

• Journal of Korean Society on Water Environment
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• v.33 no.6
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• pp.736-743
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• 2017

In this study, 4-nonylphenol (4-NP), an endocrine disrupting chemical, was removed by ozone treatment processes under the various experimental conditions including UV irradiation, $TiO_2$ addition. The ozone flow rate and concentration were maintained at $1.0L{\cdot}min^{-1}$ and $70{\pm}5mg{\cdot}L^{-1}$. The pH, COD and TOC of the samples were obtained every 10 minutes for 60 minutes in laboratory scale batch reactor. We found that the combination of UV irradiation and $TiO_2$ addition for ozonation improves the removal efficiency of COD and TOC in 4-NP aqueous solution. In case of the $O_3/UV/TiO_2$ system, COD and TOC were greatly reduced to 85.3 ~ 94.0% and 89.2 ~ 97.2%, respectively. 4-NP degradation rate constants, $k_{COD}$ and $k_{TOC}$, were calculated based on the COD and TOC values. Significantly, $k_{COD}$ and $k_{TOC}$ were improved in the $O_3/UV/TiO_2$ treatment process compared with single $O_3$ process, because the oxidation and the mineralization of 4-NP were increased by generating of the hydroxyl radical. The $k_{COD}$ and $k_{TOC}$ were obtained to be $5.81{\times}10^{-4}{\sim}10.8{\times}10^{-4}sec^{-1}$ and $11.9{\times}10^{-4}{\sim}19.4{\times}10^{-4}sec^{-1}$ in the $O_3/UV/TiO_2$ process. Activation energy ($E_a$) of ozone oxidation reaction based on $k_{COD}$ and $k_{TOC}$ were increased in order of $O_3/UV/TiO_2$ < $O3/UV$ < $O_3/TiO_2$ < $O_3$ process. It was confirmed that the addition of $TiO_2$ and UV irradiation to the ozone oxidation reaction significantly reduced the $E_a$ value and the degradation of 4-NP.

• Bulletin of the Korean Chemical Society
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• v.31 no.4
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• pp.925-928
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• 2010

Nitrogen-doped $TiO_2$ ($TiO_2$:N) nano-particles with a pure anatase crystalline structure were successfully synthesized through the hydrolysis of $TiCl_4$ in an ammonia aqueous solution. The samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), $N_2$-sorption, and UV-vis diffuse reflectance spectra (UV-vis DRS) techniques. The absorption edge of nitrogen-doped $TiO_2$ shifted into the visible wavelength region. The photoelectrochemical (PEC) performances were investigated for the $TiO_2$ mesoporous electrodes doped with different nitrogen concentrations. The $TiO_2$:N electrodes exhibited much higher PEC responses compared to the pure $TiO_2$ electrode because of the significantly enhanced visible-photoresponsibility of the $TiO_2$:N electrodes.

• Applied Chemistry for Engineering
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• v.1 no.1
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• pp.35-43
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• 1990

A series of $TiO_2-SiO_2$catalysts were prepared by coprecipitation from the mixed solution of titanium tetrachloride and sodium silicate. Some of the samples were treated with 1N $H_2SO_4$ and used as modified catalysts. The catalytic activities of modified catalysts were higher than those of unmodified catalysts, and the effect of modification on the catalytic activity was higher for 2 - propanol dehydration than for cumene dealkylation. The catalytic activity of unmodified catalysts was correlated with their acid amount for the above two reactions. As $TiO_2-SiO_2$ catalysts had relatively large amount of weak acid sites and small amount of strong acid sites, the catalytic activity for 2 - propanol dehydration was higher than that for cumene dealkylation. The effect of modification on catalytic activity increased with increasing $TiO_2$content of the catalysts. Actually, $92-TiO_2-SiO_2/SO_4{^2}$had the highest increment in catalytic activity and $10-TiO_2-SiO_2/SO_4{^2}$had the lowest increment for the 2 - propanol dehydration.

• Journal of the Korean Electrochemical Society
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• v.14 no.1
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• pp.27-32
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• 2011

The electorchemical properties of $Li_4Ti_5O_{12}$ added with Cr was tested. The addition or substitution of atoms to $Li_4Ti_5O_{12}$ are expected to modify the crystal structure, and therefore to change the electrochemical performances of $Li_4Ti_5O_{12}$. After the spinel structure $Li_4Ti_{5-x}Cr_xO_{12}$ (x = 0~0.2) were obtained via sol-gel method, the gel was heated in a muffle furnace at $800{\sim}850^{\circ}C$ for 12 h in air. The physical properties of the samples were characterized by TG-DTA, XRD, SEM, FT-IR, and the electrochemical properties were tested with battery cycler at 0.01~2.0 V range. The $Li_4Ti_5O_{12}$ exhibited 169.9 mAh/g at 1C and capacity recovery was 97.5% of the initial capacity at 0.1C. $Li_4Ti_{4.9}Cr_{0.1}O_{12}$ (Cr 1% added) showed best performance of 193.8 mAh/g at 1C and the capacity recovery was increased to 98.8% of the initial capacity at 0.1C.

• Korean Journal of Materials Research
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• v.11 no.8
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• pp.690-696
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• 2001

$TiO_2$ coated coal fly ash has been prepared in order to develop the low price $TiO_2$ photocatalyst and spread out its utilizing field. $TiO_2$ particles is coated on the surface of coal fly ash by precipitation method. In this method, $TiCl_4$ aqueous solution was used as a titanium stock solution and $NH_4HCO_3$ was used as a precipitant. The titanium hydroxide precipitated on the surface of coal fly ash in these neutralizing reaction process was oxidized by heat treatment in temperature ranges of $300~700^{\circ}C$. The crystal structure of the generated titanium dioxide showed anatase type. The crystal size of titanium dioxide increased with raising the temperature of heat treatment, but the removal ability of NO gas decreased. When the titanium dioxide was heated at temperature ranges of $300~ 400^{\circ}C$ for 2 hours, the crystal size of titanium dioxide appeared about 9nm, and the removal rate of NO gas showed 85~ 92%. The whiteness of $TiO_2$ coated coal fly ash increased with raising the coating rate of titanium dioxide and the temperature of heat treatment.

• Journal of the Korean Ceramic Society
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• v.37 no.10
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• pp.933-937
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• 2000

고기능성 전자재료용 TiO$_2$분말 및 박막제조에 사용되는 중간생성물인 TiCl$_4$는 99% 이상의 고순도가 요구된다. 고순도.미립의 TiO$_2$분말 및 TiCl$_4$는 황산법으로 제조한 저순도 TiO$_2$원료를 사용하여 염소화법으로 Ti-염화물 및 염화불순물로 제조한 후, 대부분의 염화불순물들은 3단계 과정을 거쳐 고순화 하였다. 대부분의 염화불순물은 분리.응축 및 분별증류로, VOCl$_3$는 mineral oil을 첨가하여 비등점을 변화시켜, 그리고 미량의 염화불순물은 열가수분해하여 침전시킨 후 유기용제 처리하여 제거하였다. 유기용제 처리는 TiO$_2$분말의 고순도화에 도움이 되었으며, 입자간의 응집을 적게 하여 TiO$_2$입자크기도 작아졌다. 또한 anatase에서 rutile 결정구조로의 전이온도도 낮아지는 부수적인 효과를 보였다.

• Journal of the Korean Ceramic Society
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• v.31 no.5
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• pp.471-476
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• 1994

The influence of TiO2 addition on the sintering and microstructure of magnesia ceramics was studied. An excess amount of TiO2 over the solid solubility limit reacted with magnesia to form Mg2TiO4 compound above 130$0^{\circ}C$. The deviation of lattice parameter of MgO was estimated to be under 0.2% when existence of TiO2 in MgO. The addition of TiO2 markedly promoted the densification of MgO at comparatively low temperature and the sintered density of about 98% of the theorectical was obtained at 150$0^{\circ}C$, 2h. The densification was mainly governed by grain growth of MgO and the effect of Mg2TiO4 existing as a second phase on depression of grain growth of MgO was not exhibited.

• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.583-590
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• 1997

The effects of Mn2O3 and Y2O3 additives on the microstructure and dielectric properties of Sr(Zr, Ti)O3 have been investigated. Powders with Sr(Zr1-xTix)O3(0$\leq$x$\leq$0.1) composition were prepared by the conventional solid state processing from commercial TiO2 and precipitation-processed ZrO2. The powders containing sintering additives of Mn2O3 and Y2O3 were compacted and then sintered at 1,55$0^{\circ}C$ for 4 h to get>97% relative density. Mn2O3 suppressed the grain growth and Y2O3 enhanced the density of sintered body. The oxidation state of Mn ions were determined by a chemical wet method and EPR spectroscopy. Mn ions were present as Mn2+ and Mn4+ in SrZrO3, while as Mn3+ and Mn4+ in Ti-substituted Sr(Zr, Ti)O3. With the substitution of Ti, the lattice parameters of SrZrO3 decreased and its dielectric constant increased with remarkable decrease in Q value. The dielectric constant of Sr(Zr, Ti)O3 was in the range of 30 to 40, Q values 1,200~5,400 at 6 GHz and temperature coefficient of resonant frequency -67~100 ppm/K.

• Korean Journal of Crystallography
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• v.6 no.1
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• pp.1-13
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• 1995

Cr:A12O3 and Ti:A12O3 single crystals were grown by Czochralski method, and the effects of crystal growth parameters such as pulling rate, rotation rate, dopant and growth atmosphere on crystal quality were investigated. And spectroscopic properties including lasing efficiency were also measured. Single crystals, sized of 20mm in diameter and 100-135mm in length, were successfully grown from the seed of <001> direction. With the doping level of 0.5w/o Cr2O3, pulling rate 2.0mm/hr, rotation rate of 30rpm and inert atmosphere by nitrogen gas, high quality crystals of Cr:A12O3 were grown. While in case of Ti:A12O3 crystals, high quality crystals were grown under the conditions of the doping level of 0.25w/o TiO2, pulling rate of 1.5mm/hr, rotation rate of 30rpm and reducing atmosphere by hydrogen - nitrogen mixed gas. It was confirmed that Cr3+ ion which maintains its ionoc valence during growth easily de-bubbled than Ti4+ ion which changes its valence, Fe3+ ion also has do-bubbling effect to Ti:A12O3 crystal and the reducing atmosphere by 90% N2 - 10% H2 mixed gas gave effective result on the changing of Ti4+ to Ti3+ and de-bubbling. As a result of spectroscopic measurements of Cr:A12O3 crystal, 4A2 →4F2 and 4F1 absorption transitions and E →4A2(R1) and 2A →4A2(R2) fluorenscence transitions were confirmed. And it was measured that wavelengths of laser R1 and R2 transitions were 696±5nm and 692±5nm respectively, line width of these transitions were 12A, and life-time of fluorenscence was 152μsec. In case of Ti:A12O3 crystals, it was confirmed that absortion transition of 4T2→4E and fluorescence transition of 4E→4T2 with wide range of 650-1050nm was occured. And 147μsec of life-time of fluorescence, 125.4 of figure of merit and 9% of laser efficience were also measured.