• Journal of Powder Materials
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• v.27 no.5
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• pp.381-387
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• 2020

In this work, TiO₂ 3D nanostructures (TF30) were prepared via a facile wet chemical process using ammonium hexafluorotitanate. The synthesized 3D TiO₂ nanostructures exhibited well-defined crystalline and hierarchical structures assembled from TiO₂ nanorods with different thicknesses and diameters, which comprised numerous small beads. Moreover, the maximum specific surface area of TiO₂ 3D nanostructures was observed to be 191 ㎡g^-1, with concentration of F ions on the surface being 2 at%. The TiO₂ 3D nanostructures were tested as photocatalysts under UV irradiation using Rhodamine B solution in order to determine their photocatalytic performance. The TiO₂ 3D nanostructures showed a higher photocatalytic activity than that of the other TiO₂ samples, which was likely associated with the combined effects of a high crystallinity, unique features of the hierarchical structure, a high specific surface area, and the advantage of adsorbing F ions.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.16.1-16.1
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• 2011

$TiO_2$ is a promising material for gas sensors. To achieve high sensitivities, the material should exhibit a large surface-to-volume ratio and possess the high accessibility of the gas molecules to the surface. Accordingly, a wide variety of porous $TiO_2$ nanomaterials synthesized by wet-chemical methods have been reported for gas sensor applications. Nonetheless, achieving the large-area uniformity and comparability with well-established semiconductor production processes of the methods is still challenging. An alternative method is soft-templating which utilizes nanostructured inorganic or organic materials as sacrificial templates for the preparation of porous materials. Fabrication of macroporous $TiO_2$ films and hollow $TiO_2$ tubes by soft-templating and their gas sensing applications have been reported recently. In these porous materials composed of assemblies of individual micro/nanostructures, the form of links or necks between individual micro/nanostructures is a critical factor to determine gas sensing properties of the material. However, a systematic study to clarify the role of links between individual micro/nanostructures in gas sensing properties of a porous metal oxide matrix is thoroughly lacking. In this work, we have demonstrated a fabrication method to prepare highly-ordered, embossed $TiO_2$ films composed of anatase $TiO_2$ hollow hemispheres via soft-templating using polystyrene beads. The form of links between hollow hemispheres could be controlled by $O_2$ plasma etching on the bead templates. This approach reveals the strong correlation of gas sensitivity with the form of the links. Our experimental results highlight that not only the surface-to-volume ratio of an ensemble material composed of individual micro/nanostructures but also the links between individual micro/nanostructures play a critical role in evaluating the sensing properties of the material. In addition to this general finding, the facileness, large-scale productivity, and compatability with semiconductor production process of the proposed fabrication method promise applications of the embossed $TiO_2$ films to high-quality sensors.

• Rapid Communication in Photoscience
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• v.1 no.1
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• pp.13-15
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• 2012

New porous $TiO_2$ nanostructures with shapes of pearl and rice were synthesized by hydrothermal treatment of $TiO_2$-liposome nanocomposites in acid and base solutions, respectively, as identified by scanning electron microscopy (SEM), transmission electron microscopy (TEM) images and large Brunauer-Emmett-Teller (BET) surface areas. The x-ray diffraction (XRD) patterns and selected area electron diffraction proved them to be well-defined anatase crystals. Their UV-visible reflectance absorption spectra were observed to have low band gap energy (3.03 and 3.07 eV, respectively), exhibiting surface absorption band in the visible range from 400 to 600 nm. The degradation of methylene blue (MB) over the $TiO_2$ nanostructures was observed upon visible-light irradiation, which was found to be very efficient as compared with any other conventional visible-light responsive $TiO_2$ nanostructures.

• Bulletin of the Korean Chemical Society
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• v.34 no.12
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• pp.3635-3640
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• 2013

We prepared Ni and Pd-modified $TiO_2@SiO_2$ core-shell nanostructures and then analyzed them by scanning electron microscopy, optical microscopy, X-ray diffraction crystallography, FT-IR and UV-Visible absorption spectroscopy. In addition, their CO oxidation performance was tested by temperature-programmed mass spectrometry. The CO oxidation activity showed an order of Ni-$TiO_2@SiO_2$ ($900^{\circ}C$) < Ni-$TiO_2@SiO_2$ ($90^{\circ}C$) < Ni-$TiO_2@SiO_2$ ($450^{\circ}C$) in the first CO oxidation run, and greatly improved activity in the same order in the second run. The $T_{10%}$ (the temperature at 10% CO conversion) corresponds to the CO oxidation rate of $2.8{\times}10^{-5}$ molCO $g{_{cat}}^{-1}s^{-1}$. For Ni-$TiO_2@SiO_2$ ($450^{\circ}C$), the $T_{10%}$ was observed at $365^{\circ}C$ in the first run and at $335^{\circ}C$ in the second run. For the Pd-$TiO_2@SiO_2$ ($450^{\circ}C$), the $T_{10%}$ was observed at a much lower temperature of $263^{\circ}C$ in the first CO oxidation run, and at $247^{\circ}C$ in the second run. The CO oxidation activities of transition metal modified $TiO_2@SiO_2$ core-shell nanostructures presented herein provide new insights that will be useful in developing catalysts for various environments.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.34-34
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• 2010

Activities of various $TiO_2$ nanostructures in photocatalytic decomposition of methylene blue and toluene were determined in order to shed light on the relationship between structures and photocatalytic activity. Commercially available P-25 samples were used in the present work. In addition, $TiO_2$ nanostructures were synthesized using atomic layer deposition (ALD). We show that change in the surface structure of $TiO_2$ upon variois surface treatments results in variation in photocatalytic activity. In particular, increase in the number of OH groups on the surface leads to the enhancement in photocatalytc activity. Surface OH groups increases adsorption reactivity of organic reactants, thereby increasing activity in photocatalytic decomposition of methylene blue and toluene.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.95.2-95.2
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• 2017

Anodic TiO2 nanostructures have wide applications due to their various functional properties such as wide band-gap, chemical stability, and anti-corrosiveness. In order to enhance the properties, several approaches to fabricate TiO2 structures have been developed. Especially, TiO2 nanotube arrays prepared by anodization in a fluoride electrolyte show impressive properties for dye sensitized solar cells1 and photocatalyst. In this presentation, we introduce new types of TiO2 nanostructures beyond TiO2 nanotubes that are fabricated by anodization at high temperature in a glycerol/phosphate electrolyte. We show that depending on the anodization parameters different self-organized morphologies - of highly aligned, high aspect ratio oxide structures can be formed. Critical factor for growth and the use for dye sensitized solar cells and photocatalyst will be discussed.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.2
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• pp.139-145
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• 2015

In this paper, the flexible piezoelectric nanocomposite generator(NCG) device based on $BaTiO_3$ nanostructures was fabricated via simple and low-cost spin coating method. The $BaTiO_3$ nanostructures synthesized by self-assembly reaction showed dendrite morphologies. To produce the piezoelectric nanocomposite(p-NC layer) which acts as an electric energy source in NCG device, the piezoelectric nanopowders($BaTiO_3$) were dispersed in polydimethylsiloxane(PDMS). Sequently, the p-NC layer was inserted in two dielectric layer of PDMS; these layers enabled the NCG device flexibility as well as durability prohibiting detachment(exfoliation) for significantly mechanical bending motions. The fabricated NCG device shows average maximum open circuit voltage of 6.2 V and average maximum current signals of 300 nA at 20 wt% composition of $BaTiO_3$ nanostructures in p-NC layer. Finally, the flexible energy harvester generates stable output signals at any rate of frequency which were used to operate LCD device without any external energy supply.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.663-663
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• 2013

We prepared Cu oxides, and Ni and Pd-TiO2@SiO2 core-shellnanostructures, and tested their CO oxidation performances by temperature-programmed mass spectrometry. We found the starting temperatures of CO oxidation are around $200^{\circ}C$ and $300^{\circ}C$ for Ni and Pd-TiO2@SiO2 nanostructures, respectively. Cu oxides are cubes with 50~200 nm with, prepared with different concentrations of NaOH and ascorbic acid. For the core-shell structures, we prepared 100 nm SiO2 spheres, first coated the surface with TiO2 precursor, and then coated with Ni and Pd. Their characteristics are further examined by scanning electron microscopy, optical microscope, FT-IR, and UV-Vis absorption spectroscopy.

• Applied Chemistry for Engineering
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• v.28 no.4
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• pp.375-382
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• 2017

In the present review, we provide an overview of the research trend of anodic $TiO_2$ nanostructures. To date, most anodic $TiO_2$ nanostructure formation has focused on the fluoride ion electrolyte system to form nanotube layers. Recently, a novel approach that describes the formation of thick, self-organized $TiO_2$ nanostructures was reported. These layers can be prepared on Ti metal by anodization in a hot organic/$K_2HPO_4$ electrolyte. This nanostructure consists of a strongly interlinked network of nanosized $TiO_2$, and thus provides a considerably higher specific surface area than that of using anodic $TiO_2$ nanotubes. This review describes the formation mechanism and novel properties of the new nanostructures, and introduces potential applications.

• Bulletin of the Korean Chemical Society
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• v.33 no.5
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• pp.1699-1702
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• 2012

$TiO_2$ nanostructures with various morphologies like cubes, spheres, hexahedral pillars and spherical tubes were synthesized by microwave-assisted hydrothermal process. Each structure was obtained by changing the relative concentrations of titanium tetraisoproxide (TTIP), tetrabutylammonium hydroxide (TBAH) and ethanol. Scanning electron microscopy (SEM), transmission electoron microscopy (TEM), X-ray diffraction and Brunauer-Emmett-Teller (BET) surface area analysis were used to characterize the synthesized $TiO_2$ nanostructures. From these results, it has been proved that $TiO_2$ structure could be controlled to have specific morphology, size, surface area, pore volume and pore size distribution.