Nam-Hee Lee

Preparation and Characterization of Silica/Polyamide-imide Nanocomposite Thin Films

The functional silica/polyamide-imide composite films were prepared via simple ultrasonic blending, after the silica nanoparticles were modified by cationic surfactant—cetyltrimethyl ammonium bromide (CTAB). The composite films were characterized by scanning electron microscope (SEM), thermo gravimetric analysis (TGA) and thermomechanical analysis (TMA). CTAB-modified silica nanoparticles were well dispersed in the polyamide-imide matrix, and the amount of silica nanoparticles to PAI was investigated to be from 2 to 10 wt%. Especially, the coefficients of thermal expansion (CET) continuously decreased with the amount of silica particles increasing. The high thermal stability and low coefficient of thermal expansion showed that the nanocomposite films can be widely used in the enamel wire industry.

Structure-tunable synthesis of titanate nanotube thin films via a simple hydrothermal process

In this study, titanium metal acts as the titanium source to prepare oriented titanate nanotube thin film. The effects of preparation parameters, such as reaction temperature, duration and post-treatment conditions, on the film morphology and stability have been examined. A general formation mechanism for oriented titanate nanotube thin film is proposed on the basis of detailed observations of the products using two-dimensional surface SEM studies and TEM images. The overall formation of titanate nanotubes can be summarized as a sequence of four steps: (a) titanium dissolution and alkali titanate hydrogel formation; (b) alkali titanate hydrogel dissolution, increased TiO32−, TiO2(OH)22− or TinO2n+m2m− concentration and layered Na2Ti3O7 formation; (c) layered Na2Ti3O7 growth; (d) nanotube formation via Na2Ti3O7 splitting and the multilayer scrolling process. The Na2Ti3O7 lamellar structures split between the (010) planes into nanosheets.

Photocatalytic Properties of Nanotubular-Shaped Powders with Anatase Phase Obtained from Titanate Nanotube Powder through Various Thermal Treatments

Photocatalytic properties of nanotubular-shaped titanate powders, synthesized by hydrothermal treatment of , were studied after calcinations at various temperatures and times under , air, and H2 atmospheres. Their photocatalytic properties were measured with checking decomposition of 4-chlorophenol under UV-A irradiation, together with physical characterizations using SEM, TEM, XRD, BET, and Raman spectroscopy. With increasing calcination temperature and time, nanotubular-shaped titanate particles became short, rod-like, or irregular by oversintering, and their crystalline structure was changed into anatase phase. The photocatalytic ability in decomposition of 4-chlorophenol using the calcined powders showed the highest value due to obtainment of high specific area by maintaining nanotubular shape, together with transformation from titanate to anatase phase having perfect crystallinity in or air atmosphere.

Phase transition control of nanostructured TiO2 powders with additions of various metal chlorides

Formation behavior and photo-oxidation abilities of nanostructured TiO2 powders were investigated through a direct crystallization from aqueous TiOCl2 solutions containing various metal chlorides at 100??C. The obtained TiO2 powders without any additives and those with Ni2+, Fe3+ and Nb5+ ions added, which have a similar positive ionic radius to Ti4+, were mainly crystallized with rutile phase, whereas those with Al3+ and Zr4+ ions added, which have a quite different positive ionic radius, were mainly crystallized with anatase phase. On the other hand, the secondary particles in the TiO2 powder consisted of acicular and spherical primary particles, corresponding to rutile and anatase phases, respectively. From these results, it seems that the positive ionic radius of the additives would affect phase formation as well as morphology of TiO2 precipitates. Among the TiO2 powders prepared, Ni-added powder, which consisted mainly of rutile phase with a small amount of anatase phase, showed excellent photocatalytic ability in decomposition of 4-chlorophenol.

Synthesis and photocatalytic properties of nano bi-crystalline titania of anatase and brookite by hydrolyzing TiOCl2 aqueous solution at low temperatures

Well-dispersed nano-anatase or bi-crystalline (anatase + brookite) titania powders with a average crystal size below 10 nm have been prepared from aqueous TiOCl2 solution by adjusting pH values of starting solution and adding different additives at low temperatures. Amorphous–anatase transformation of titania could proceed in a liquid–solid reaction at low temperatures, even around room temperature, by catalytic support of H+ ion. The presence of a small amount of SO2−4ion is also unfavorable to the formation of both rutile and brookite. By carefully adjusting preparation conditions, nano pure anatase with higher surface area, good crystallinity and a very good photocatalytic activity for gas-phase oxidation of benzene was obtained.

Preparation of Nanostructured TiO2 Powders with Additions of Various Metal–Chlorides for Efficient Photocatalyst

Preparation of nanostructured TiO2 powders for efficient photocatalyst was investigated through a direct crystallization from aqueous TiOCl2 solutions containing various metal–chlorides. The TiO2 powders without any additives and those added with Ni2+, Fe3+ and Nb5+ions, respectively, which has a similar cationic radius to Ti4+, were mainly crystallized to rutile phase, whereas those added with Al3+ and Zr4+ ions, which have a quite different positive ionic radius, were mainly crystallized to anatase phase. On the other hand, the secondary particles in the TiO2 powder consisted of acicular and spherical primary particles corresponding to rutile and anatase phases, respectively. From these results, it seems that the cationic radius of the additives could affect phase formation as well as morphology of TiO2 precipitates. Among the TiO2 powders prepared, Ni2+ doped powder, showing mainly rutile phase, had excellent photocatalytic ability in decomposition of 4-chlorophenol.

Preparation of Ultra-Thin Transparent TiO 2 Coated Film by Ink-Jet Printing Method

Dye sensitized solar cells(DSSC) are the most promising future energy resource due to their high energy efficiency, low production cost, and simple manufacturing process. But one problem in DSSC is short life time compared to silicon solar cells. This problem occurred from photocatalytic degradation of dye material by nanometer sized particles. To prevent dye degradation as well as to increase its life time, the transparent coating film is needed for UV blocking. In this study, we synthesized nanometer sized particles in sols by increasing its internal pressure up to 200 bar in autoclave at for 10 hrs. The synthesized sols were all formed with brookite phase and their particle size was several nm to 30 nm. Synthesized sols were coated on the backside of fluorine doped tin oxide(FTO) glass by ink jet printing method. With increasing coating thickness by repeated ink jet coating, the absorbance of UV region (under 400 nm) also increases reasonably. Decomposition test of titania powders dispersed in 0.1 mM amaranth solution covered with coating glass shows more stable dye properties under UV irradiation, compared to that with as-received FTO glass.