Jirapon Khamwannah

Extreme superomniphobicity of multiwalled 8 nm TiO2 nanotubes.

We report unprecedented superomniphobic characteristics of nanotube-structured TiO(2) surface fabricated by electrochemical etching and hydrothermal synthesis process, with the wettability contact angles for water and oil both being ∼174° or higher. A tangled forest of ∼8-nm-diameter, multiwalled nanotubes of TiO(2) was produced on the microtextured Ti surface, with the overall nanotube length controlled to 150 nm by adjusting the processing time. Wettability measurements indicate that the nanotube surface is extremely nonwettable to both water and oil. The contact angle of the 8 nm TiO(2) nanotube surface after perfluorosilane coating is extremely high (178°) for water droplets indicating superhydrophobic properties. The contact angle for oil, measured using a glycerol droplet, is also very high, about 174°, indicating superoleophobic characteristics. These dual nonwetting properties, superomniphobic characteristics, are in sharp contrast to the as-made TiO(2) nanotubes which exhibit superhydrophilic properties with a contact angle of essentially ∼0°. Such an extreme superomniphobic material made by a simple and versatile method can be useful for a variety of technical applications. It is interesting to note that all three properties can be obtained with identical nanotube structures. A nanometer-scaled structure introduced by hydrothermally grown TiO(2) nanotubes is an effective air trapping nanostructure in enhancing the amphiphobic (superomniphobic) wettability.

Improved dye sensitized solar cell performance in larger cell size by using TiO2 nanotubes

Typical dye sensitized solar cells (DSSCs) exhibit a severe reduction of power conversion efficiency when the cell size is increased. In order to cope with this issue, we have investigated the use of anodized TiO(2) nanotubes on Ti foil in combination with the standard TiO(2) nanoparticle paste coated anode structure. The presence of nanotubes in the anode structure enabled a significant mitigation of the size-dependent deterioration of the DSSC performance, with a trend of much milder decrease of the efficiency as a function of the cell dimension up to 9 cm(2). The observed improvement is partly attributed to the elimination of fluorine-doped tin oxide glass in the anode structure, as well as the enhanced charge collection via the nanotube coated Ti substrate, resulting from enhanced mechanical and electrical connections and possibly improved light trapping. The introduction of TiO(2) nanotubes on the Ti foil substrate led to a substantial improvement of the J(sc) current density.

Nanocomposites of TiO2 and double-walled carbon nanotubes for improved dye-sensitized solar cells

It is demonstrated that an incorporation of double-walled carbon nanotubes (DWCNTs) into a TiO2 photo-anode layer results in a significant improvement in the overall energy conversion performance in the dye-sensitized solar cell (DSSC). Comparing to the standard TiO2 anode, the carbon nanotube-containing TiO2 anode with 0.2 wt. % DWCNTs has boosted up the photocurrent density (Jsc) by 43%. The DSSC power conversion efficiency was also improved from ∼3.9% in the case of carbon nanotube-free TiO2 anode to as high as 6.4% with the addition of DWCNTs upon optimized anode annealing. The observed enhancement in the solar cell performance in the presence of the carbon nanotubes is attributed primarily to the noticeable reduction in microcracking and associated robust electrical conduction. Some contribution of the electrical conducting nature of the filler material (DWCNTs) to the improved DSSC properties may be possible; however, it is viewed as a minor effect, considering the small amount of the nanotubes used.

Magnetically Vectored Delivery of Cancer Drug Using Remotely On–Off Switchable NanoCapsules

Hollow-sphere-structured magnetic nanocapsules containing intentionally trapped iron oxide nanoparticles and anticancer drugs have been prepared to provide a powerful magnetic vector under moderate gradient magnetic fields. It is shown that these nanocapsules can penetrate into the interior of tumors and allow a controlled on-off switchable release of the anticancer drug cargo via remote 100 KHz RF field. This smart drug delivery system is nanoscale compact, with the drug molecules and magnetic nanoparticles contained within the hollow capsules having ~ 80 ~ 150nm diameter. In vitro results using a mouse model indicate that such a nanocapsule-mediated, on-demand drug release is effective in reducing tumor cell growth.

Plasmonic Au nanoparticles on 8 nm TiO2 nanotubes for enhanced photocatalytic water splitting

We report here for the first time a successful distribution and attachment of fine Au nanoparticles on ∼8 nm diameter TiO2 nanotubes having significantly increased surface area. Au thin film deposition onto hydrothermally grown TiO2 nanotube arrays followed by thermal annealing breaks up the Au film into desired, uniformly distributed nanoparticles. Visible light absorption spectra of the gold nanoparticles on TiO2 nanotubes indicate that the Au nanoparticles are photo-excited due to plasmon resonance, and charge separation is accomplished by the transfer of photoexcited electrons from the gold particle to the TiO2 conduction band, thereby enhancing photoelectrochemical performance. By virtue of substantially increased surface area with the 8 nm TiO2 nanotube substrate in combination with the plasmonic effect of distributed Au nanoparticles, significantly increased photocurrent density was obtained with extended light absorbance from the UV regime to the visible spectrum region. Such gold nanoparticle dec...

Externally triggered on-demand drug release and deep tumor penetration

Hollow-sphere-shaped nanocapsules containing intentionally inserted magnetic nanoparticles and predefined anticancer drugs provide a powerful magnetic vector under moderate gradient magnetic fields. They enable the nanocapsules to penetrate into the tumors and allow a controlled on-off switchable release of the anticancer drug cargo inside the tunors by remotely applied RF magnetic field. This smart drug delivery system, which can also be made imageable, is compact in geometry because the drug molecules and magnetic nanoparticles can all be self-contained within ∼150 nm capsules. In vitro results indicate that the nanocapsules are effective in reducing tumor cell growth.

Geometrically Planar Ion-Implant Patterned Magnetic Recording Media Using Block Copolymer Aided Gold Nanoisland Masks

We have developed patterned media via ion implantation using Au nano mask approach for local control of coercivity of magnetically hard [Co/Pd]n multilayer film. Au nano-islands produced through a di-block copolymer templated technique is used as the mask for ion implantation. The sputter deposited [Co 0.3 nm/Pd 0.8 nm]8/Pd 3 nm/Ta 3 nm multilayer film having vertical magnetic anisotropy is coated with a diblock copolymer layer, two phase decomposed into vertically pored nanostructure, then chemically processed to nucleate gold nanoislands corresponding to the diblock copolymer nanostructures. Subsequent nitrogen (N) ion implantation, using these Au islands as implantation-blocking masks, allows a patterned penetration of implanted ions into unmasked portion of the [Co/Pd]n multilayer film, thus creating invisible but magnetically isolated bit island geometry while maintaining the overall flat configuration of the patterned media.