• Korean Journal of Metals and Materials
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• v.47 no.2
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• pp.91-98
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• 2009

The titania nanotubular layer for photocatalytic application was synthesized by anodization process in HF solution and the photocatalytic efficiencies of nanotubular film were evaluated by the decomposition rate of aniline blue. In order to facilitate the photocatalytic reaction, the electron acceptors such as potassium bromate, hydrogen peroxide and ammonium persulfate were added to aniline blue solution and the effects of electron acceptors on the dye degradation efficiency were evaluated. The results showed that the photocatalytic efficiency has markedly improved by adding the electron acceptors.

• The Journal of Korean Academy of Prosthodontics
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• v.49 no.1
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• pp.16-21
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• 2011

Purpose: The purpose of this study was to investigate the bioactivity of precalcified nanotubular $TiO_2$ layer on Ti-6Al-7Nb alloy. Materials and methods: Anodic oxidation was carried out at a potential of 20 V and current density of 20 mA/$cm^2$ for 1 hour. The glycerol solution containing 1 wt% $NH_4F$ and 20 wt% deionized water was used as an electrolyte. Precalcification treatment was obtained by soaking in $Na_2HPO_4$ solution at $80^{\circ}C$ for 30 minutes followed by soaking in saturated $Ca(OH)_2$ solution at $100^{\circ}C$ for 30 minutes, followed by heat treatment at $500^{\circ}C$ for 2 hours. To evaluate the activity of precalcified nanotubular $TiO_2$ layer, specimens were immersed in a simulated body fluid with pH 7.4 at $36.5^{\circ}C$ for 10 days. Results: 1. Nanotubular $TiO_2$ layer showed the highly ordered dense structure by interposing small diameter nanotubes between large ones, the shape of nanotubes was enlarged as going down. 2. The mean length of nanotubes was $517.0{\pm}23.2\;nm$ innm glycerol solution containing 1 wt% $NH_4F$ and 20 wt% $H_2O$ at 20 V for 1 hour. 3. The bioactivity of Ti-6Al-7Nb alloy was improved with formation of nanotubular $TiO_2$ layer and precalcification treatment in $80^{\circ}C$ 0.5 M $Na_2HPO_4$ and saturated $100^{\circ}C$ $Ca(OH)_2$ solution. Conclusion: Bioactivity of precalcified nanotubular $TiO_2$ layer on Ti-6Al-7Nb alloy was improved.

• Korean Journal of Metals and Materials
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• v.50 no.2
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• pp.164-170
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• 2012

Nanotubular structure formation on the Ti-6Al-4V and Ti-Ta alloy surfaces by electrochemical methods has been studied using the anodizing method. A nanotube layer was formed on Ti alloys in 1.0 M $H_3PO_4$ electrolyte with small additions of $F^-$ ions. The nanotube nucleation and growth of the ${\alpha}$-phase and ${\beta}$-phase appeared differently, and showed different morphology for Cp-Ti, Ti-6Al-4V and Ti-Ta alloys. In the ${\alpha}$-phase of Cp-Ti and martensite ${\alpha}^{\prime}$ and in the ${\alpha}^{{\prime}{\prime}}$ and ${\beta}$-phase of the Ti-Ta alloy, the nanotube showed a clearly highly ordered $TiO_2$ layer. In the case of the Ti-Ta alloy, the pore size of the nanotube was smaller than that of the Cp-Ti due to the ${\beta}$-stabilizing Ta element. In the case of the Ti-6Al-4V alloy, the ${\alpha}$-phase showed a stable porous structure; the ${\beta}$-phase was dissolved entirely. The nanotube with two-size scale and high order showed itself on Ti-Ta alloys with increasing Ta content.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.111-111
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• 2013

골이식 부위에서 연조직의 붕괴를 막아주면서 골이식재를 위한 안정적인 공간을 확보하기 위해서 타이타늄 메쉬가 적용된다. 본 연구에서 생체 불활성의 특성을 보이는 타이타늄 차폐막에 양극산화와 석회화 순환처리에 의해서 생체활성을 부여한 결과, 골형성을 촉진하는 결과를 보여주었다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.239.1-239.1
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• 2011

Dye sensitized solar cells (DSC) are promising devices for inexpensive, nontoxic, transparent, and large-scale solar energy conversion. Generally thick $TiO_2$ nanoporous films act as efficient photoanodes with their large surface area for absorbing light. However, electron transport through nanoparticle networks causes the slowdown and the loss of electron transport because of a number of interparticle boundaries inside the conduction path. We have studied DSCs with precisely dimension-controlled $TiO_2$ nanotubes array as photoanode. $TiO_2$ nanotubes array is prepared by template-directed fabrication method with atomic layer deposition. Well-ordered nanotubes array provides not only large surface area for light absorbing but also direct pathway for electrons with minimalized grain boundaries. Large enlongated anatase grains in the nanotubes could enhance the conductivity of electrons, but also suppress the recombination with holes through defect sites during diffusion into the electrode. To study the effect of grain boundaries, we fabricated two kinds of nanotubes which have different grain sizes by controlling deposition conditions. And we studied electron conduction through two kinds of nanotubes with different grain structures. The solar cell performance was studied as a function of thickness and grain structures. And overall solar-to-electric energy conversion efficiencies of up to 7% were obtained.

• Journal of the Korean Vacuum Society
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• v.19 no.2
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• pp.105-113
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• 2010

One-dimensional nanostructures have been researched widely because of its unique physical properties such as optical, electrical, mechanical, and chemical properties in comparison with bulk structures. Especially nanotubular structures are able to provide larger surface area, capability to load purposeful materials, and unique mechanical modulus. We reviewed the oxide nanotube technology with focusing on the method of template-directed fabrication. We can easily control of physical dimensions of nanotubes by control of nanotemplate and fabrication condition. and template-directed fabrication is ideal tool to fabricate the amount of monodisperse nanotubes. They have potentials for application in solar cell, drug-delivery, Li-ion batteries and photocatalyst. We discussed these potential applications and research trends.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.68-68
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• 2018

Nanoporous or nanotubular metal oxide can be fabricated by anodization of metal substrate in fluoride contained electrolytes. The approach allows various transition metals such as Zr, Hf, Nb, Ta to form highly ordered oxide nanostructures. These oxide nanostructures have various advantages such as high surface area, fast electron transport rate and slow recombination in semiconductive materials. Recently, vanadium oxide nanostructures have been drawn attentions due to their superior electronic, catalytic and ion insertion properties. However, anodization of vanadium metal to form oxide layers is relatively difficult due to ease formation of highly soluble complex in water contained electrolyte during anodization. Yang et al. reported $[TiF_6]^{2-}$ or $[BF_4]^-$ in electrolyte helps to formation of stable oxide layer [1, 2]. However, the reported approaches are very sensitive in other parameters. In this presentation, we deal with the other important key parameters to form ordered anodic vanadium oxide such as pH, temperatures and applied potential.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.75.2-75.2
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• 2013

Atomic layer deposition (ALD), utilizing self-limiting surface reactions, could offer promising perspectives for future efficient energy conversion devices. The capabilities of ALD for surface/interface modification and construction of novel architectures with sub-nanometer precision and exceptional conformality over high aspect ratio make it more valuable than any other deposition methods in nanoscale science and technology. In the context, a variety of researches on fabrication of active materials for energy conversion applications by ALD are emerging. Among those materials, one-dimensional nanotubular titanium dioxide, providing not only high specific surface area but also efficient carrier transport pathway, is a class of the most intensively explored materials for energy conversion systems, such as photovoltaic cells and photo/electrochemical devices. The monodisperse, stoichiometric, anatase, TiO2 nanotubes with smooth surface morphology and controlled wall thickness were fabricated via low-temperature template-directed ALD followed by subsequent annealing. The ALD-grown, anatase, TiO2 nanotubes in alumina template show unusual crystal growth behavior which allows to form remarkably large grains along axial direction over certain wall thickness. We also fabricated dye-sensitized solar cells (DSCs) introducing our anatase TiO2 nanotubes as photoanodes, and studied the effect of blocking layer, TiO2 thin films formed by ALD, on overall device efficiency. The photon convertsion efficiency ~7% were measured for our TiO2 nanotubebased DSCs with blocking layers, which is ~1% higher than ones without blocking layer. We also performed open circuit voltage decay measurement to estimate recombination rate in our cells, which is 3 times longer than conventional nanoparticulate photoanodes. The high efficiency of our ALD-grown, anatase, TiO2 nanotube-based DSCs may be attributed to both enhanced charge transport property of our TiO2 nanotubes photoanode and the suppression of recombination at the interface between transparent conducting electrode and iodine electrolytes by blocking layer.

• Korean Journal of Materials Research
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• v.23 no.4
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• pp.240-245
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• 2013

Electrochemical surface treatment is commonly used to form a thin, rough, and porous oxidation layer on the surface of titanium. The purpose of this study was to investigate the formation of nanotubular titanium oxide arrays during short anodization processing. The specimen used in this study was 99.9% pure cp-Ti (ASTM Grade II) in the form of a disc with diameter of 15 mm and a thickness of 1 mm. A DC power supplier was used with the anodizing apparatus, and the titanium specimen and the platinum plate ($3mm{\times}4mm{\times}0.1mm$) were connected to an anode and cathode, respectively. The progressive formation of $TiO_2$ nanotubes was observed with FE-SEM (Field Emission Scanning Electron Microscopy). Highly ordered $TiO_2$ nanotubes were formed at a potential of 20 V in a solution of 1M $H_3PO_4$ + 1.5 wt.% HF for 10 minutes, corresponding with steady state processing. The diameters and the closed ends of $TiO_2$ nanotubes measured at a value of 50 cumulative percent were 100 nm and 120 nm, respectively. The $TiO_2$ nanotubes had lengths of 500 nm. As the anodization processing reached 10 minutes, the frequency distribution for the diameters and the closed ends of the $TiO_2$ nanotubes was gradually reduced. Short anodization processing for $TiO_2$ nanotubes of within 10 minutes was established.

• Korean Journal of Materials Research
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• v.29 no.12
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• pp.790-797
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• 2019

To improve photocatalytic performance, CdS nanoparticle deposited TiO₂ nanotubular photocatalysts are synthesized. The TiO₂ nanotube is fabricated by electrochemical anodization at a constant voltage of 60 V, and annealed at 500 for crystallization. The CdS nanoparticles on TiO₂ nanotubes are synthesized by successive ionic layer adsorption and reaction method. The surface characteristics and photocurrent responses of TNT/CdS photocatalysts are investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-Vis spectrometer and LED light source installed potentiostat. The bandgaps of the CdS deposited TiO₂ photocatalysts are gradually narrowed with increasing of amounts of deposited CdS nanoparticles, which enhances visible light absorption ability of composite photocatalysts. Enhanced photoelectrochemical performance is observed in the nanocomposite TiO₂ photocatalyst. However, the maximum photocurrent response and dye degradation efficiency are observed for TNT/CdS30 photocatalyst. The excellent photocatalytic performance of TNT/CdS30 catalyst can be ascribed to the synergistic effects of its better absorption ability of visible light region and efficient charge transport process.