• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.2
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• pp.315-323
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• 1998

$TiO_2$films of rutile and anatase phase have been prepared on silica glass substrates by the sol-gel method using $Ti(i-OC_3H_7)_4$. The effect of additives on the polymorph of $TiO_2$film has been examined in view of degree of crystallization. Third-order nonlinear optical properties of the both film have been investigated by the third harmonic generation method. The measured 3rd order nonlinear optical susceptibility of rutile and anatase thin films were about $1.4{\times}10^{-12}$ and $9.7{\times}10^{-13}$ esu, respectively.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1256-1257
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• 2008

Dye-Sensitized Solar Cell(DSSC) is a new type of solar cell by using photocatalytic properties of $TiO_2$. The size and shape of $TiO_2$ particle are two of important parameters that are related to the characteristics of DSSC. And these can be changed by controlling $TiO_2$ sintering conditions especially temperature. The particles of $TiO_2$ are classified anatase and rutile. Anatase particles are created at low sintering temperature and rutile particles are created at high sintering temperature. Anatase particles have advantages such as increased surfaces that cause more attached dye molecules, and fast electron transportation. And rutile particles have advatages such as more efficient light scattering. Therefore, we studied characteristics of DSSC in this paper as $TiO_2$ sintering temperature is varied. As a result, we found that characteristics of DSSC are very good in the case that anatase and rutile particles are together and this sintering temperature is 450$^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.466.1-466.1
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• 2014

$TiO_2$는 저렴한 가격, 적절한 bandgap, 열적, 화학적, 생물학적 안정성 등으로 촉망받는 광촉매 물질이다. $TiO_2$는 rutile (tetragonal, space group: P42/mnm), anatse (tetragonal, space group: I41/amd), and brookite (orthorhombic, space group: Pbca )의 3가지 대표적인 결정구조를 가지고 있다. Rutile과 anatase는 1972년 Fujishima와 Honda가 $TiO_2$의 광촉매 특성을 발견 한 후로 아주 많은 연구가 되어왔다. 반면 brookite의 경우는 자연에 거의 존재하지 않으며, 합성방법도 어려워서 rutile과 anatase에 비해 많은 연구가 되지 않았다. 본 연구에서는 brookite를 포함한 다양한 $TiO_2$ 나노구조를 간단한 수열합성법으로 티타늄 호일 위에 합성하였다. 합성된 $TiO_2$는 반응 온도와 시간, additive의 농도에 따라서 sheet, tube, wire, pyramidal 의 4가지 morphologies를 가졌다. 이 다양한 morphologies은 SEM과 TEM으로 분석되었으며, 각 물질의 결정 구조는 XRD분석과 TEM의 SAED pattern 분석으로 sheet, tube, wire은 anatase, pyramidal 구조는 brookite라는 것이 확인 되었다. 위의 방법으로 합성된 각각의 $TiO_2$ 물질들을 working 전극으로, Pt와 Ag/AgCl을 reference와 counter 전극으로 만들어서 photoelectrochemical 특성을 측정해서 비교를 해보았을 때, brookite 물질이 anatase보다 더 좋은 photoelectrochemical 특성을 나타내는 것을 확인하였다.

• Bulletin of the Korean Chemical Society
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• v.33 no.6
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• pp.1989-1992
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• 2012

We present a low temperature (${\approx}70^{\circ}C$) method to prepare anatase, vertically aligned feather-like $TiO_2$ (VAFT) nanowire arrays $via$ reactive pulsed DC magnetron sputtering. The synthesis method is general, offering a promising strategy for preparing crystalline nanowire metal oxide films for applications including gas sensing, photocatalysis, and 3rd generation photovoltaics. As an example application, anatase nanowire films are grown on fluorine doped tin oxide coated glass substrates and used as the photoanode in dye sensitized solar cells (DSSCs). AM1.5G power conversion efficiencies for the solar cells made of 1 ${\mu}m$ thick VAFT have reached 0.42%, which compares favorably to solar cells made of the same thickness P25 $TiO_2$ (0.35%).

• Bulletin of the Korean Chemical Society
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• v.25 no.9
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• pp.1341-1345
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• 2004

We developed a novel synthesis strategy of titania nanowire arrays by employing simple hydrothermal reaction and ion-exchange reaction techniques. Hydrothermal reactions of metallic titanium powder with $H_2O_2$ in a 10 M NaOH solution produced a new sodium titanate compound, $Na_2Ti_6O_{13}{\cdot}xH_2O$ (x~4.2), as arrays of nanowires of lengths up to 1 mm. Acid-treatment followed by calcination of this material produced arrays of highly crystalline anatase nanowires as evidenced by x-ray diffraction, Raman spectroscopy, and transmission electron microscopy studies. In both cases of sodium titanate and anatase, the nanowires have exceptionally large aspect ratios of 10,000 or higher, and they form arrays over a large area of $1.5 {\times} 3 cm^2$. Observations on the reaction products with varied conditions indicate that the array formation requires simultaneously controlled formation and crystal growth rates of the $Na_2Ti_6O_{13}{\cdot}xH_2O$ phase.

• Journal of the Korean Ceramic Society
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• v.37 no.4
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• pp.308-313
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• 2000

Hydrous titanium oxide particles with anatase phase were prepared from 0.05 mol TiCl4 solution using NH4HCO3 as precipitant by the droopping precipitant method. The sequential change of pH is completed by a sudden and steep increase in a pH value of the range of 6~7 to which the concentration of adsorbed OH- and H+ ions on TiO2 surface is equal. Rutile phase started precipitating with anatase phase as an increase of reaction temperature above 6$0^{\circ}C$ in aqueous 0.05mol TiCl4 solution and its specific surface area was found to decrease from 452 $m^2$/g($25^{\circ}C$) to 164$m^2$/g(8$0^{\circ}C$). Specific surface area decreased rapidly when anatase powders precipitated at 4$0^{\circ}C$ were heat-treated at temperature higher 40$0^{\circ}C$. FT-IR result confirmed that it was due to the decrease of OH species within hydrous titanium oxides. The loss of ethanol after illumination of the powder heated at $600^{\circ}C$ and $700^{\circ}C$ for 4 h was 66 and 68.8%, respectively.

• Composites Research
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• v.31 no.6
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• pp.365-370
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• 2018

One of the critical parameters to improve the output power for triboelectric nanogenerators (TENGs) is the surface charge density. In this work, we modify the tribo-material of TENG by introducing the $TiO_x$ embedded Polydimethylsiloxane (PDMS) in anatase and rutile phase. The effect of dielectric constant and electronic structure of the $TiO_x$ on the capacitance of TENG and the output power as well are discussed. The surface charge density is increased as the control of the dielectric constant in difference weight percent of $TiO_x$ and PDMS. As the results of that, the 5% $TiO_x$ rutile phase and 7% $TiO_x$ anatase phase embedded PDMS exhibit the highest TENG output. The peak value of voltage/current obtained from $TiO_x$ rutile and anatase phase are ${\sim}180V/8.2{\mu}A$ and $211.6V/8.7{\mu}A$, respectively, at the external force of 5 N and working frequency of 5 Hz, which gives over 12-fold and 15-fold power enhancement compared with the TENG based on the pristine PDMS film. This study provides a better understanding for TENG performance enhancement from the materials view.

• Journal of Welding and Joining
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• v.24 no.5
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• pp.57-61
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• 2006

For the production of functional $TiO_2$-biodegradable plastic (polybutylene succinate:PBS) composite material with photocayalytic activity, we attempted to prepare $TiO_2$ coatings on PBS substrate by HVOF and plasma spraying techniques under various conditions. The microstructures of coatings were characterized with SEM and XRD analysis, and the photocatalytic efficiency of coatings was evaluated by the photo degradation of gaseous acetaldehyde. The effects of primary particle size and spraying parameters on the formation behavior, photocatalytic performance of the coatings have been investigated. The results indicated that for both the HVOF sprayed $P_{200}$ and $P_{30}$ coatings, the high anatase ratio of 100% can be achieved regardless of fuel gas pressure. On the other hand, the HVOF sprayed $P_7$ coating exhibited a largely decreased anatase ratio (from 100% to 49.1%) with increasing the fuel gas pressure, which may be attributed to much higher susceptibility of heat for 7 nm agglomerated powder. HVOF sprayed $P_{200}$ and $P_{30}$ coatings show better performance as compared to that of plasma sprayed $P_{200}$ coatings owing to the higher anatase ratio. However, the HVOF sprayed $P_7$ coatings did not show the photocatalytic activity, which may result from the extremely small reaction surface area to the photocatalytic activity and low anatase ratio.

• Analytical Science and Technology
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• v.14 no.1
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• pp.15-20
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• 2001

Photocatalytic $TiO_2$ films were prepared by anodic oxidation at 180 V and their structural difference caused by oxidation conditions was studies. The microstructure of $TiO_2$ films in $H_2SO_4$ and $H_2SO_4/H_2O_2$ solution was mixed type of rutile and anatase. However, the $TiO_2$ layer formed in $H_2SO_4/H_3PO_4$ and $H_2SO_4/H_3PO_4/H_2O_2$ mixture was mostly anatase type. All $TiO_2$ films prepared by anodic oxidation exhibited photocatalytic properties. The photocatalytic degradation of aniline blue was first order reaction with similar rate constants at all oxidative conditions examined in this work.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.466.2-466.2
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• 2014

The Quantum dot (QD) solar cells have been under active research due to their high light harvesting efficiencies and low fabrication cost. In spite of these advantages, there have been some problems on the charge collection due to the limitation of the diffusion length. The modification of advanced nanostructure is capable of solving the charge collection problem by increasing diffusion length of electron. One dimensional nanomaterials such as nanorods, nanowires, and nanotubes may enhance charge collection efficiency in QD solar cells. In this study, we synthesized $TiO_2$ anatase nanorod arrays with length of 200 nm by two-step sol-gel method. The morphology and crystal structure for the nanorod were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The anatase nanorods are single-crystalline and possess preferred orientation along with (001) direction. The photovoltaic properties for the heterojunction structure QD solar cells based on the anatase nanorod were also characterized. Compared with conventional $TiO_2$ nanoparticle based QD solar cells, these nanostructure solar cells exhibited better charge collection properties due to long life time measured by transient open circuit studies. Our findings demonstrate that the single crystalline anatase nanorod arrays are promising charge transport semiconductors for heterojunction QD solar cells.