• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.16 no.5
• /
• pp.216-221
• /
• 2006

An investigation of the influence of $WO_3$ and $V_2O_5$ catalysts on the microstructure, phase formation and selective catalytic reduction (SCR) efficiency of the synthesized SCR powders has been carried out. A commercial anatase-$TiO_2$ was used as the catalysts support. For $WO_3(10wt%)/TiO_2$, the W loading to the $TiO_2$ support led to the lower in anatase to rutile transition temperature from $1200^{\circ}C$ of $TiO_2$ support to ${\sim}900^{\circ}C$. The transition temperature was also lowered to below $650^{\circ}C$ in the $V_2O_5$(5 and 10 wt%) added composition. The $WO_3(10wt%)/TiO_2$ SCR powder obtained at $450^{\circ}C$ showed near 100% of $NO_x$ conversion efficiency at $350{\sim}400^{\circ}C$ and for the powder prepared at $650^{\circ}C$ the same efficiency was achieved in wider temperature range $300{\sim}400^{\circ}C$. The highest $NO_x$ conversion efficiency of 100% was obtained in the $V_2O_5(5wt%)/TiO_2$ SCR composition calcined at $650^{\circ}C$ in the relatively wider temperature range $250{\sim}350^{\circ}C$, while the catalytic efficiency considerably decreased for the $V_2O_5(10wt%)/TiO_2$. The lowered conversion efficiency of $NO_x$ observed in the $V_2O_5(10wt%)/TiO_2$ composition calcined at $650^{\circ}C$ was considered to be correlated with the lowered surface area resulting from the increased crystallite growth by highly reactive vanadium loading.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.30 no.5
• /
• pp.194-199
• /
• 2020

By controlling the composition of the metal-oxide nanosheet having a two-dimensional layered crystal structure, material properties and application can be extended. In this study, the composition of the nanosheet could be expanded from pure composition to doping composition by successfully synthesizing the TiO₂ nanosheet doped with Nb. Specifically, the doping composition was designed when synthesizing the layered metal oxide as a starting material (K_0.8Ti_1.73-xNb_xLi_0.27O₄, x = 0, 0.03, 0.07) and chemical exfoliation was performed. By doing this, it was possible to obtain the Nb-doped TiO_y ultrathin nanosheet. The size of the nano sheet was 2 ㎛ or less based on the long length in the x-y direction, and the thickness was about 1 nm. Nb-doping was confirmed by XRD and SEM-EDS analysis.

• Korean Chemical Engineering Research
• /
• v.53 no.5
• /
• pp.632-637
• /
• 2015

Mesoporous $TiO_2$ granules were prepared by spray pyrolysis using nano-sized titania particles which were synthesized by a hydrothermal method, and they were evaluated as the photoanode of dye-sensitized solar cells. To enhance the cell efficiency, nanoparticles within granules were chemically interconnected by adding titanium ethoxide (TEOT) to colloidal spray solution. The resulting titania particles had anatase phase without forming rutile. $TiO_2$ granules obtained showed about 400 nm in size, the specific surface area of $74-77m^2/g$, and average pore size of 13-17 nm. The chemical modification of $TiO_2$ granules by adding TEOT initially to the colloidal spray solution was proved to be an effective way in terms of increasing both the light scattering within photoanode and the lifetimes of photo-excited electrons. Consequently, the light-harvesting efficiency of TEOT-modified granules (${\eta}=6.72%$) was enhanced about 14% higher than primitive nanoparticles.

• Journal of the Korean Ceramic Society
• /
• v.52 no.1
• /
• pp.9-12
• /
• 2015

Nano-structured electrodes were fabricated to develop efficient photoelectrochemical conversion systems for the synthesis of hydrogen from water and hydrocarbon fuels from $CO_2$. In this work, we compared the photoactivity of rutile $TiO_2$ nanorods grown on FTO and SEED/FTO by a hydrothermal method. An analysis of the microstructures showed that the density of nanorod/SEED/FTO samples, which showed only the (002) peak in their x-ray diffraction patterns, was two times higher than that of a nanorod/FTO sample. The photocurrent density of nanorod/SEED/FTO samples was increased by as much as 40% of the photocurrent density of the nanorod/FTO sample due to the increased specific density of the nanorods. However, the transient time for a recombination of photogenerated electrons and holes was 20 times faster in the nanorod/SEED/FTO. The seed layers are discussed as possible recombination sites.

• Bulletin of the Korean Chemical Society
• /
• v.35 no.8
• /
• pp.2512-2518
• /
• 2014

The praseodymium-doped $TiO_2$ photocatalyst samples, which could degrade methyl orange under UV irradiation, were prepared by sol-microwave method for improving the photocatalytic activity of $TiO_2$. The resulting materials were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectra, Fourier transform infrared spectra (FTIR) and Ultraviolet-visible diffuse reflectance spectra (UV-vis DRS). It was found Pr doping retarded the growth of crystalline size and the phase transformation from anatase to rutile, and narrowed the band gap energy. Praseodymium doping brought about remarkable improvement in the photoactivity. The optimal dopant amount of Pr was 2% by molar of cement and the calcination temperature was $500^{\circ}C$ for the best photocatalytic activity. The improvement of photocatalytic activity was ascribed to the occurrence of lattice distortion and the effective containment of the recombination of the electron-hole by $Pr^{3+}$.

• Journal of Surface Science and Engineering
• /
• v.43 no.2
• /
• pp.97-104
• /
• 2010

In this paper, we conducted MATLAB simulation using the reflectance formula and the Planck's black body radiation principle, for the purpose of identifying the opimum material and thickness of anti-reflective coating from double layered structures. We found that the optimum condition was obtained when refractive index of upper layer is 1.44 and that of lower layer is 2.29. As materials close to these refractive indices, $MgF_2$ as the upper layer and $HfO_2$, ZnS, $TiO_2$ as the lower layer were suggested. The best result in an average reflectance of 2.759% was obtained from a double layered structure of $MgF_2$ 94 nm/ZnS 55 nm.

• Journal of the Korean Magnetics Society
• /
• v.10 no.5
• /
• pp.220-224
• /
• 2000

Ultra-fine $Co_{1+x}$F $e_{2-}$2x/ $Ti_{x}$ $O_4$ferrite powders have been prepared by the sol-gel method. The crystallographic and magnetic properties of the sample have been investigated by means of x-ray diffraction, Mossbauer spetroscopy and vibrating sample magnetometry. The formation of nano crystallized particles is confirmed. The x-ray diffractions of all samples with various compositions clearly indicate the presence of spinel structure. The Mossbauer spectra could be fitted as the superposition of two sextets due to F $e^{3+}$ A-site and B-site. The IS and QS values nearly constant with substituted Co-Ti contents, whereas $H_{hf}$ of B-site decreases with increasing Co-Ti substitution in $Co_{1+x}$F $e_{2-}$2x/ $Ti_{x}$ $O_4$. The magnetic behaviour of powders shows that the saturation magnetization and the coercivity decrease with increasing x in $Co_{1+x}$F $e_{2-}$2x/ $Ti_{x}$ $O_4$.$.X>.

• Environmental Engineering Research
• /
• v.19 no.3
• /
• pp.255-259
• /
• 2014

In this research, we compared the COD removal efficiencies of titanium dioxide ($TiO_2$) thin films coated on the surfaces of borosilicate glass that prepared by three different numbers of coating layer; i) 3 layers ii) 4 layers and iii) 5 layers by sol-gel method. All of the prepared $TiO_2$ thin films consisted of pure anatase crystalline structure with grain sizes in the range 20-250 nm. The calculated optical band gaps of the $TiO_2$ thin films were 3.24. The total apparent surface area per total weight of $TiO_2$ thin films were 4.74, 3.86 and $2.79m^2g^{-1}$ for 3, 4 and 5 layers coating, respectively. The kinetics of the photodegradation reactions of COD under UVA light source were described by the Langmuir-Hinshelwood (L-H) kinetic model. The specific rates of the photodegradation of $TiO_2$ thin films at 3 layers coating was $1.40{\times}10^{-4}min^{-1}mW^{-1}$, while for the 4 layers coating and the 5 layers coating were $1.50{\times}10^{-4}$ and $4.60{\times}10^{-4}min^{-1}mW^{-1}$, respectively. The photocatalytic performance of COD degradation was higher with smaller grain size, higher surface area and narrow optical band gaps. Moreover, the numbers of coating layer on substrate also have great influence for kinetic of COD removal.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.430.1-430.1
• /
• 2014

According to advanced nanotechnology in the field of biomedical engineering, many studies of the interaction between topography of surfaces and cellular responses have been focused on nanostructure. In order to investigate this interaction, it is essential to make well-controlled nanostructures. Electron beam lithography (EBL) have been considered the most typical processes to fabricate and control nano-scale patterns. In this work, $TiO_2$ nanowire array was fabricated with hybrid process (top-down and bottom-up processes). Nanodot arrays were patterned on the substrate by EBL process (top-down). In order to control the spacing between nanodots, we optimized the EBL process using Poly(methyl methacrylate) (PMMA) as an electron beam resist. Metal lift-off was used to transfer the spacing-controlled nanodots as a seed pattern of $TiO_2$ nanowire array. Au or Sn nanodots which play an important role for catalyst using Vapor-Liquid-Solid (VLS) method were patterned on the substrate through the lift-off process. Then, the sample was placed in the tube furnace and heated at the synthesis temperature. After heat treatment, $TiO_2$ nanowire array was fabricated from the nanodots through VLS method (bottom-up). These results of spacing-controlled nanowire arrays will be used to study the interaction between nanostructures and cellular responses in our next steps.

• Journal of the Korean Ceramic Society
• /
• v.53 no.6
• /
• pp.682-688
• /
• 2016

In $TiO_2$-CuO systems, low-temperature sinterability was investigated by a conventional sintering method. Sintering temperatures were set at under $950^{\circ}C$, at which the volume diffusion is inactive. The temperatures are less than the melting point of Ag ($961^{\circ}C$), which is often used as an internal conductor in low-temperature co-fired ceramic technology. To optimize the amount of CuO dopant, various dopant contents were added. The optimum level for enhanced densification was 2 wt% CuO. Excess dopants were segregated to the grain boundaries. The segregated dopants supplied a high diffusion path, by which grain boundary diffusion improved. At lower temperatures in the solid state region, grain boundary diffusion was the principal mass transport mechanism for densification. The enhanced grain boundary diffusion, therefore, improved densification. In this regard, the results of this study prove that the sintering mechanism was the same as that of activated sintering.