• Title, Summary, Keyword: $TiO_2$ nanotubes

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$TiO_2$ Nanotubes Preparation and Its Formation Mechanism

  • Kang, Young-Gu;Shin, Ki-Seok;Ahn, Sung-Hwan;Hahm, Hyun-Sik
    • Journal of the Korean Applied Science and Technology
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    • v.27 no.4
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    • pp.487-493
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    • 2010
  • There has been a controversy on the formation mechanism of $TiO_2$ nanotubes. This study was conducted to elucidate the formation mechanism of $TiO_2$ nanotubes. $TiO_2$ nanotubes were prepared by a hydrothermal method. $TiO_2$ nanotubes formation mechanism was investigated by controlling the formation time. It was found that $TiO_2$ nanotubes were formed by growing, not by wrapping of sheets. The phase structure of hydrogen titanate nanotubes was different from that of $TiO_2$ nanotubes. It is important to wash the sodium titanate nanotubes with an acidic solution to get hydrogen titanate nanotubes and then to calcine the hydrogen titanate nanotubes around $400^{\circ}C$ to obtain $TiO_2$ nanotubes.

Fabrication of dye-sensitized solar cells using a both-ends-opened TiO2 nanotube/nanoparticle hetero-nanostructure

  • Hossain, Md Ashraf;Oh, Sehyun;Lim, Sangwoo
    • Journal of Industrial and Engineering Chemistry
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    • v.51
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    • pp.122-128
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    • 2017
  • We fabricated a hetero-structure photoanode with both-ends-opened $TiO_2$ nanotubes and $TiO_2$ nanoparticles for dye-sensitized solar cells (DSSCs). Two-step anodization and selective etching process were used to obtain the both-ends-opened $TiO_2$ nanotubes. A heat treatment was employed to obtain anatase crystal-structured nanotubes. The effect of the both-ends-opened $TiO_2$ nanotubes on the photoelectric conversion efficiency (PCE) of the DSSCs was evaluated by positioning the $TiO_2$ nanotubes on $TiO_2$ nanoparticle layers and by sandwiching them between the $TiO_2$ nanoparticles. It is suggested that both-ends-opened $TiO_2$ nanotubes serve as incident light scattering layers that lead to superior light harvesting efficiency of DSSCs. This increases the electron lifetime and results in the recycling of more light by dye molecules, thus increasing the photocurrent density. Consequently, a high PCE of 7.74% was obtained when the $TiO_2$ nanotubes were placed on the $TiO_2$ nanoparticles and a PCE of 8.56% was obtained when the $TiO_2$ nanotubes were placed between the $TiO_2$ nanoparticles.

Photoelectrochemical Properties of TiO2 Nanotubes by Well-Controlled Anodization Process (양극산화 제어에 의한 TiO2 나노튜브의 광전기화학 특성)

  • Jeong, Dasol;Kim, Donghyun;Jung, Hyunsung
    • Journal of the Korean institute of surface engineering
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    • v.52 no.6
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    • pp.298-305
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    • 2019
  • We investigated a correlation between morphology and photoelectrochemical properties of TiO2 nanotubes fabricated by well-controlled anodization processes. Anodization in an ethylene-glycol-based electrolyte solution accelerated the rapid grow rate of TiO2 nanotubes, but also cause problems such as delamination at the interface between TiO2 nanotubes and a Ti substrate, and debris on the top of the nanotube. The applied voltages for the anodization of TiO2 were adjusted to avoid the interface delamination. The heat treatment and the anodizing time were also controlled to enhance the crystallinity of the as-prepared TiO2 nanotubes and to increase the surface area with the varied length of the anodized TiO2 nanotubes. Additionally, a 2-step anodization process was utilized to remove the debris on the tube top. The photoelectrochemical properties of TiO2 nanotubes prepared with the carefully tailored conditions were investigated. By removing the debris on TiO2 nanotubes, applied bias photon-to-current efficiency (ABPE) of TiO2 nanotubes increased up to 0.33%.

Effects of Heat Treatment and Viologen Incorporation on Electrochromic Properties of TiO2 Nanotubes (열처리 및 바이올로젠 도입에 따른 TiO2 나노튜브의 전기변색 특성)

  • Cha, Hyeongcheol;Nah, Yoon-Chae
    • Journal of Korean Powder Metallurgy Institute
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    • v.23 no.2
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    • pp.102-107
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    • 2016
  • We demonstrate the electrochromic properties of $TiO_2$ nanotubes prepared by an anodization process and investigate the effects of heat treatment and viologen incorporation on them. The morphology and crystal structure of anodized $TiO_2$ nanotubes are investigated by scanning electron microscopy and X-ray diffraction. As-formed $TiO_2$ nanotubes have straight tubular layers with an amorphous structure. As the annealing temperature increases, the anodized $TiO_2$ nanotubes are converted to the anatase and rutile phases with some cracks on the tube surface and irregular morphology. Electrochemical results reveal that amorphous $TiO_2$ nanotubes annealed at $150^{\circ}C$ have the largest oxidation/reduction current, which leads to the best electrochromic performance during the coloring/bleaching process. Viologen-anchored $TiO_2$ nanotubes show superior electrochromic properties compared to pristine $TiO_2$ nanotubes, which indicates that the incorporation of a viologen can be an effective way to enhance the electrochromic properties of $TiO_2$ nanotubes.

Anodic Growth of Large Inner Diameter TiO2 Nanotubes (TiO2 나노튜브 내경 확장을 위한 양극산화 조건)

  • Lee, Hyeon-Kwon;Oh, Hyunchul;Lee, Kiyoung
    • Journal of the Korean institute of surface engineering
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    • v.51 no.1
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    • pp.27-33
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    • 2018
  • In the present work, we demonstrate the feasibility to form large inner diameter $TiO_2$ nanotubes by anodization of Ti in a HF/ethylene glycol electrolyte. In order to achieve the large inner diameter $TiO_2$ nanotubes, optimization of the anodization condition is required. We discover the key factors in the formation of large inner diameter $TiO_2$ nanotubes are concentration of water in the electrolyte, anodization temperatures, and high-applied potential. Under optimum conditions, the inner diameters of $TiO_2$ nanotubes are 379 nm. The results are approximately 3 folders larger than the general case.

Morphological Studies on TiO2 Nanotubes Formed by Anodizing in Aqueous and Non-Aqueous Solutions (수용액 및 비수용액에서 양극산화법으로 형성된 TiO2 나노튜브의 구조 연구)

  • Kim, Byung-Jo;Moon, Sung-Mo;Jeong, Yong-Soo;Kim, Byung-Kwan
    • Journal of the Korean institute of surface engineering
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    • v.43 no.4
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    • pp.180-186
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    • 2010
  • $TiO_2$ nanotubes were formed on Ti by anodizing in 1 M $H_3PO_4$ + 0.3 M HF and 0.1 M $NH_4F$ + 2% $H_2O$ in ethylene glycol, and their surface and cross-sectional morphologies were observed using FE-SEM as a function of anodizing time and applied voltage. The cross-section of the $TiO_2$ nanotubes was readily observed from the small pieces of nanotubes remaining near the scratch lines after scratching of the anodized surface. $TiO_2$ nanotubes was observed to grow faster and thicker in non-aqueous solution than in aqueous solution. Diameter of $TiO_2$ nanotubes was proportional to the applied voltage, irrespective of the type of the electrolyte, and it is recommended to use non-aqueous solutions for the preparation of larger diameter of $TiO_2$ nanotubes.

Highly Ordered TiO2 nanotubes on pattered Si substrate for sensor applications

  • Kim, Do-Hong;Shim, Young-Seok;Moon, Hi-Gyu;Yoon, Seok-Jin;Ju, Byeong-Kwon;Jang, Ho-Won
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.66-66
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    • 2011
  • Anodic titanium dioxide (TiO2) nanotubes are very attractive materials for gas sensors due to its large surface to volume ratios. The most widely known method for fabrication of TiO2 nanotubes is anodic oxidation of metallic Ti foil. Since the remaining Ti substrate is a metallic conductor, TiO2 nanotube arrays on Ti are not appropriate for gas sensor applications. Detachment of the TiO2 nanotube arrays from the Ti Substrate or the formation of electrodes onto the TiO2 nanotube arrays have been used to demonstrate gas sensors based on TiO2 nanotubes. But the sensitivity was much lower than those of TiO2 gas sensors based on conventional TiO2 nanoparticle films. In this study, Ti thin films were deposited onto a SiO2/Si substrate by electron beam evaporation. Samples were anodized in ethylene glycol solution and ammonium fluoride (NH4F) with 0.1wt%, 0.2wt%, 0.3wt% and potentials ranging from 30 to 60V respectively. After anodization, the samples were annealed at $600^{\circ}C$ in air for 1 hours, leading to porous TiO2 films with TiO2 nanotubes. With changing temperature and CO concentration, gas sensor performance of the TiO2 nanotube gas sensors were measured, demonstrating the potential advantages of the porous TiO2 films for gas sensor applications. The details on the fabrication and gas sensing performance of TiO2 nanotube sensors will be presented.

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Improved Conversion Efficiency of Dye-sensitized Solar Cells Based on TiO2 Porous Layer Coated TiO2 Nanotubes on a Titanium Mesh Substrate as Photoanode

  • Lim, Jae-Min;He, Weizhen;Kim, Hyung-Kook;Hwang, Yoon-Hwae
    • Current Photovoltaic Research
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    • v.1 no.2
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    • pp.90-96
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    • 2013
  • We report here flexible dye-sensitized solar cells (DSSC) based on Ti-mesh electrodes that show good mechanical flexibility and electrical conductivity. $TiO_2$ nanotube arrays prepared by electrochemical anodizing Ti-mesh substrate were used as photoanode. A Pt-coated Ti-mesh substrate was used as counter electrode. The photoanodes were modified by coating a $TiO_2$ porous layer onto the $TiO_2$ nanotubes in order to increase the specific surface area. To increase the long term stability of the DSSCs, a gel type electrolyte was used instead of a conventional liquid type electrolyte. The DSSC based on $33.2{\mu}m$ long porous $TiO_2$ nanotubes exhibited a better energy conversion efficiency of ~2.33%, which was higher than that of the DSSCs based on non-porous $TiO_2$ nanotubes.

Principle of Anodic TiO2 Nanotube Formations (양극산화를 이용한 산화 타이타늄 나노 튜브 구조 형성 원리)

  • Lee, Kiyoung
    • Applied Chemistry for Engineering
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    • v.28 no.6
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    • pp.601-606
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    • 2017
  • One-dimensional nanostructured metal oxide can be formed through an anodic oxidation, which is a typical technique of metal surface treatment. Studies on $TiO_2$ nanotubes have been widely carried out with increasing interests in $TiO_2$, which has an excellent functionality among various metal oxides. The present article reviews the principles of formation of $TiO_2$ nanotubes, which have been studied so far. In particular, the article discussed the equilibrium relationship between the oxide formation and etching, which is a key parameter of $TiO_2$ nanotube growth, and the formation of the porous structure. Furthermore, morphological considerations of $TiO_2$ nanotubes according to electrolyte conditions will be explained to the researchers who will study the application of $TiO_2$ nanotubes formed through the anodic oxidation in the future.

Effects of Surface Characteristics of TiO2 Nanotublar Composite on Photocatalytic Activity (TiO2 복합 광촉매의 표면 특성과 광촉매 효율)

  • Lee, Jong-Ho;Youn, Jeong-Il;Kim, Young-Jig;Oh, Han-Jun
    • Korean Journal of Materials Research
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    • v.24 no.10
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    • pp.556-564
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    • 2014
  • To synthesize a high-performance photocatalyst, N doped $TiO_2$ nanotubes deposited with Ag nanoparticles were synthesized, and surface characteristics, electrochemical behaviors, and photocatalytic activity were investigated. The $TiO_2$ nanotubular photocatalyst was fabricated by anodization; the Ag nanoparticles on the $TiO_2$ nanotubes were synthesized by a reduction reaction in $AgNO_3$ solution under UV irradiation. The XPS results of the N doped $TiO_2$ nanotubes showed that the incorporated nitrogen ions were located in interstitial sites of the $TiO_2$ crystal structure. The N doped titania nanotubes exhibited a high dye degradation rate, which is effectively attributable to the increase of visible light absorption due to interstitial nitrogen ions in the crystalline $TiO_2$ structure. Moreover, the precipitated Ag particles on the titania nanotubes led to a decrease in the rate of electron-hole recombination; the photocurrent of this electrode was higher than that of the pure titania electrode. From electrochemical and dye degradation results, the photocurrent and photocatalytic efficiency were found to have been significantly affected by N doping and the deposition of Ag particles.