論題 目

文 の要 旨Preparation of TiO2-based thin films with improved photocatalytic activity andsuper-hydrophobicity by plasma-enhanced chemical vapor deposition（プラズマ CVD 法による高い光触媒活性と超疎水性を有するTiO2 薄膜の作製）
氏 名 Lang Jianghua

The plasma enhanced chemical vapor deposition (PECVD) process is a practical method in film
preparation thanks to its simple operation step and relatively low cost. TiO2 films with photocatalytic
activity have been successfully prepared by PECVD methods. In addition, various TiO 2-based functional
materials can also be synthesized by the PECVD methods. By introducing foreign materials, TiO 2-based
composite often exhibits improved and new properties. In this dissertation, efforts have been made toenhance the photocatalytic activity of TiO2 thin film. In addition, a TiO2 composite film with superhydrophobic surface was fabricated by introducing a polymer.
Firstly, a TiO2-CNT-Ag (T-C-A) ternary composite film was successfully synthesized using thePECVD by simultaneously feeding a carbon nanotube (CNT)/Ag nanoparticle suspension and titaniumtetraisopropoxide (TTIP) vapor. Here, Ag nanoparticles were prepared from AgNO 3 solution in advance.
During the film deposition, a suspension containing both CNT and Ag nanoparticles were spray-dried togenerate aerosol nanoparticles of those materials. The obtained nanoparticles were fed along with TTIP
vapor into a PECVD reactor. The prepared films were evaluated by scanning electron microscopy (SEM),
transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray
photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and ultraviolet (UV)-visible spectroscopy.
Moreover, the Ag/Ti content ratio of the films was determined using an inductivity coupled plasma
optical emission spectrometer. The performance of the pristine TiO 2 (T) and TiO2-composite films forthe degradation of Rhodamine 6G was evaluated under the irradiation of simulated solar light. Ternary
structures in which CNT and Ag nanoparticles were embedded into TiO2 matrix were confirmed. Typical
thickness of the films was approximately 1 μm. The structures and optical properties of the films werealtered by the addition of CNT and Ag nanoparticles. The crystal structure of the films was influenced
by the temperature at which the films have been heated (annealed). The addition of CNT and Agnanoparticles was found to significantly improve the performance of TiO2, where the photocatalytic
activity of T-C-A was approximately 1.8 times higher than that of T. In addition, a commercial TiO 2
powder (P25) is prepared as a thin film and used as a reference. The T-C-A film with anatase-rutile mixed
phase shows a better photocatalytic performance than self-made P25 film.
Next, a simplified PECVD process for the preparation of TiO2-Ag nanoparticle composite films wasstudied. Here, aerosolized droplets of AgNO3 solution and TTIP vapor were used as the precursors of Ag
nanoparticles and TiO2 film, respectively. Notably, the use of PECVD eliminates the need of preparing
Ag nanoparticles in advance, and is thus expected to increase the process efficiency. The deposited films
were characterized by UV-visible spectroscopy, XRD, XPS, SEM, TEM and EDS, and the effects of theconcentration of the precursors on the photocatalytic activity of the prepared films were investigated by
the degradation of methylene blue under UV-light irradiation. The Ag ions in the solution weresuccessfully reduced to metallic nanoparticles that were embedded in the TiO 2 film. The presence of Ag
nanoparticles significantly altered the morphology and bandgap of the TiO 2-Ag composite films. The

increase of AgNO3 concentration resulted in a more significant agglomeration of nanoparticles on thesurface of the films. The bandgap of the pristine TiO 2 film was 3.54 eV, while those of the TiO2-Ag
composite films decreased from 3.21 to 2.61 eV with increasing AgNO 3 concentration. And the best
photocatalytic activity was achieved for the composite film prepared by supplying 1 wt%-AgNO3.
Importantly, the photocatalytic activity was 1.75 times that of pristine TiO 2 film.
Super-hydrophobic hybrid TiO2/polydimethylsiloxane (PDMS) films were fabricated by supplying
TTIP and PDMS vapors in a PECVD process. Two different sets of experimental conditions to fabricate
the composite films were examined. The prepared composite films were characterized by SEM, TEMEDS, FTIR, XPS and XRD. The hydrophobicity was characterized by the contact angle of water dropletsstaying on the film surfaces. The photocatalytic activity was determined by the MB degradation under
UV light irradiation. It is worth noting that no curing agent was necessary in this process to immobilize
the polymer. Under the first set of experimental conditions, the presence of PDMS changed themorphology of the TiO2 matrix and inhibit the crystal growth of TiO2 very significantly. The formationof Si-O-Ti bonds indicates an interconnection between inorganic and organic components. The
photocatalytic activity of the composite film resulted in the decomposition of approximately 29% of MB
after 6 hours irradiation, which is almost the same as the pristine TiO2 film. In addition, the contact angleof the composite films before the photocatalytic activity test was approximately 157° that corresponds toa superhydrophobic surface. However, such super-hydrophobicity was lost for many products after thephotocatalytic activity tests. Under the second set of conditions, the presence of both TiO 2 and PDMS in
the films was also confirmed. The prepared films showed a photocatalytic activity that resulted in thedecomposition of 16% of MB under 6h irradiation. In addition, the super-hydrophobicity of the films,
characterized with a contact angle of 157°, was maintained after the activity tests.
Finally, the summary of the content in this dissertation was highlighted. Suggestions for the future
research for composite film fabrication by PECVD methods are also proposed