• 한국재료학회지
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• 제20권12호
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• pp.686-690
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• 2010

$TiO_2$ nanowires were self-catalytically synthesized on bare Si(100) substrates using metallorganic chemical vapor deposition. The nanowire formation was critically affected by growth temperature. The $TiO_2$ nanowires were grown at a high density on Si(100) at $510^{\circ}C$, which is near the complete decomposition temperature ($527^{\circ}C$) of the Ti precursor $(Ti(O-iPr)_2(dpm)_2)$. At $470^{\circ}C$, only very thin (< $0.1{\mu}m$) $TiO_2$ film was formed because the Ti precursor was not completely decomposed. When growth temperature was increased to $550^{\circ}C$ and $670^{\circ}C$, the nanowire formation was also significantly suppressed. A vaporsolid (V-S) growth mechanism excluding a liquid phase appeared to control the nanowire formation. The $TiO_2$ nanowire growth seemed to be activated by carbon, which was supplied by decomposition of the Ti precursor. The $TiO_2$ nanowire density was increased with increased growth pressure in the range of 1.2 to 10 torr. In addition, the nanowire formation was enhanced by using Au and Pt catalysts, which seem to act as catalysts for oxidation. The nanowires consisted of well-aligned ~20-30 nm size rutile and anatase nanocrystallines. This MOCVD synthesis technique is unique and efficient to self-catalytically grow $TiO_2$ nanowires, which hold significant promise for various photocatalysis and solar cell applications.

• 한국재료학회지
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• 제12권5호
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• pp.334-340
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• 2002

$TiO_2$-coated fly ash was synthesized by dropping method of coating agent in order to get $TiO_2$ coating layer with high photocatalytic activity on the surface of coal fly ash. The properties of the $TiO_2$ coating layer such as morphology, crystal structure, crystal size and photocatalytic activity were compared with those of the $TiO_2$-coated fly ash prepared by the traditional method of precipitation. $TiCl_4$ aqueous solution was used as a titanium stock solution and $NH_4HCO_3$ was used as a precipitant. The $TiO_2$ coating layer obtained by dropping method of coating agent was more uniform than that coated by precipitation. However, the crystal of $TiO_2$ coated by dropping method of coating agent was easy to grow by heat treatment because of the small primary particle size and bulky morphology, and its photocatalytic activity was consequently lower than that of the $TiO_2$ coated by precipitation. The $TiO_2$ coating layer obtained by both methods had a crystal structure of anatase, and the temperature of phase transformation into rutile was 90$0^{\circ}C$. The minimum crystal size of $TiO_2$ for the highest photocatalytic activity was found to be about 10nm.

• Environmental Engineering Research
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• 제16권2호
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• pp.81-90
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• 2011

Different weight percentages of Ag, Pt, and Au doped nano $TiO_2$ were synthesized using the acetic acid hydrolyzed sol-gel method. The crystallite phase, surface morphology combined with elemental composition and light absorption properties of the doped nano $TiO_2$ were comprehensively examined using X-ray diffraction (XRD), $N_2$ sorption analysis, transmission electron microscopic (TEM), energy dispersive X-ray, and DRS UV-vis analysis. The doping of noble metals stabilized the anatase phase, without conversion to rutile phase. The formation of gold nano particles in Au doped nano $TiO_2$ was confirmed from the XRD patterns for gold. The specific surface area was found to be in the range 50 to 85 $m^2$/g. TEM images confirmed the formation a hexagonal plate like morphology of nano $TiO_2$. The photocatalytic activity of doped nano $TiO_2$ was evaluated using 4-chlorophenol as the model pollutant. Au doped (0.5 wt %) nano $TiO_2$ was found to exhibit higher photocatalytic activity than the other noble metal doped nano $TiO_2$, pure nano $TiO_2$ and commercial $TiO_2$ (Degussa P-25). This enhanced photocatalytic activity was due to the cathodic influence of gold in suppressing the electron-hole recombination during the reaction.

• 한국전기전자재료학회논문지
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• 제37권3호
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• pp.231-240
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• 2024

Titanium dioxide (TiO₂) holds significant scientific and technological relevance as a key photocatalyst and resistive random-access memory, demonstrating unique physicochemical properties and serving as an n-type semiconductor. Understanding the density and arrangement of oxygen vacancies (VOs) is crucial for tailoring TiO₂'s properties to diverse technological needs, driving increased interest in exploring oxygen vacancy complexes and superstructures. In this mini review, we summarize the recent understandings of the fundamental properties of oxygen vacancies in bulk rutile (R-TiO₂) and anatase (A-TiO₂) based on DFT and beyond method. We specifically focus on the excess electrons and their spatial arrangement of disordered single VO in bulk R and A-TiO₂, aligned with the experimental findings. We also highlight the theoretical works on investigating the geometries and stabilities of ordered VOs complexes in bulk TiO₂. This comprehensive review provides insights into the fundamental properties of excess electrons in reduced TiO₂, offering valuable perspectives for future research and technological advancements in TiO₂-based devices.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.322-322
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• 2010

Recently, anti-reflective films (AR) are one of the most studied parts of a solar cell since these films improve the efficiency of photovoltaic devices. Also, anti-reflection films on the textured silicon solar cells reduce the amount of reflection of the incident light, which improves the device performance due to light trapping of incident light into the cell. Therefore, we preformed two step processes to get textured Si (100) substrate in this experiment. Pyramid size of textured silicon had approximately $2{\sim}9\;{\mu}m$. A well-textured silicon surface can lower the reflectance to 10%. For more reduced reflection, TiO2 anti-reflection films on the textured silicon were deposited at $600^{\circ}C$ using titanium tetra-isopropoxide (TTIP) as a precursor by metal-organic chemical vapor deposition (MOCVD), and the deposited TiO2 layers were then treated by annealing for 2 h in air at 600 and $1000^{\circ}C$, respectively. In this process, the treated samples by annealing showed anatase and rutile phases, respectively. The thickness of TiO2 films was about $75{\pm}5\;nm$. The reflectance at specific wavelength can be reduced to 3% in optimum layer.

• 공업화학
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• 제18권6호
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• pp.545-551
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• 2007

$TiCl_4$ 수용액의 침전반응으로 $TiO_2$를 제조할 때 침전용액의 염산농도와 반응온도 및 $Ti^{4+}$농도는 $TiO_2$ 침전물의 결정구조를 결정하는 중요한 인자이며, 이들의 조절을 통하여 브루카이트상의 부피분율 제어가 가능하다. 순수한 브루카이트상 이산화티타늄을 제조하기 위해서는 $Ti^{4+}$농도를 1.0 M 이하로 유지하고, 침전용액의 염산농도를 2.53~6.41 M이 되도록 조절한후 $70^{\circ}C$ 이하에서 20 h 침전반응 시켜야 한다. 한편, 순수한 브루카이트상 분말을 열처리한 결과 브루카이트상은 열처리 온도의 증가에 따라 아나타제상으로 상전이 된 후 최종적으로 루틸상으로 상변화가 진행되었다.

• 한국결정성장학회지
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• 제15권5호
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• pp.175-181
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• 2005

스컬용융법에 의해 루틸 단결정들을 성장시켰으며, 서로 다른 융액의 유지시간에 따른 ingot의 특성을 비교하였다. 스컬용융법은 교류전자기장(RF)에 의해 전기가 흐르는 융액의 직접유도가열에 근거하며, 가열은 RF 에너지의 흡수로 실행된다. $TiO_2$는 상온에서는 부도체이지만 온도가 올라갈수록 전기 전도성이 증가한다. 따라서, 초기 RF 유도가열을 위해 티타늄 금속 링(외경 : 6cm, 내경 : 4cm, 두께 : 0.2cm)을 $TiO_2$ 분말(아나타제상, CERAC, 3N)내부에 묻었다. 스컬용융법에 의한 산화물 용융에서 매우 중요한 것은 융점에서의 전기 저항 값, RF generator의 주파수 그리고 냉각도가니 크기이다. 본 연구에서는, $TiO_2$의 융점에서의 전기저항$(10^{-2}\~10^{-1}\;{\Omega}{\cdot}m)$은 알루미나$(10^{-1}\;{\Omega}{\cdot}m)$의 지르코니아$(10^{-3}\;{\Omega}{\cdot}m)$의 전기저항 데이터를 바탕으로 추정하였다. 냉각도가니의 내부직경은 11cm, 높이는 14cm였으며, 이것은 침투깊이$(0.36\~1.13cm)$와 RF generator 주파수를 고려하여 결정하였다

• Korean Chemical Engineering Research
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• 제53권5호
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• pp.632-637
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• 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.

• Bulletin of the Korean Chemical Society
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• 제35권8호
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• pp.2512-2518
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• 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 $Pr^{3+}$.

• 한국입자에어로졸학회지
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• 제5권1호
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• pp.1-7
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• 2009

Fe- and V-doped titanium dioxide nanoparticles consisting of spherical primary nanoparticles were synthesized from a mixed liquid precursor by using the flame spray pyrolysis. The effects of dopant concentration on the powder properties such as morphology, crystal structure, and light adsorption were analyzed by TEM, XRD, and UV-Vis spectrophotometer, respectively. As the V/Ti molar ratio increased, pure anatase particles were synthesized. On the contrary, rutile phase particles were synthesized as the Fe/Ti ratio increased. Photocatalytic property of as-prepared $TiO_2:Fe,V$ nanoparticles was investigated by measuring the removal efficiency for volatile organic compounds (VOCs) under the irradiation of visible light. After 2 hrs under visible light, the removal efficiencies of benzene, p-xylene, ethylbenzene, and toluene were reached to 21.9%, 21.4%, 19.8% and 17.6% respectively.