別紙４（課程博士）
Date of Submission:

平成 28 年 1 月 15 日
Department

Student ID Number

電気・電子情報工学専攻
Applicant’s name

氏名

奥野

学籍番号

第 093507 号

照久Supervisors

松田 厚範

指導教員

武藤 浩行

Abstract

論文内容の要旨
Title of Thesis
博士学位論文名(博士)

Shape Control of Au Nanoparticles Using Oxide Template with Ordered Tubular Mesopores andTheir Photocatalytic Properties(規則性細孔を有する酸化物鋳型を利用した金ナノ粒子の形状制御と光触媒特性)(Approx. 800 words)(要旨

1,200 字程度)

TiO 2 is generally known as a material that is nontoxic, inexpensive and able todecompose many kinds of organic compounds under sunlight. However, one drawback ofphotocatalysis by TiO 2 is that it can only be excited by ultraviolet (UV) radiation, which
occupies only a small portion of solar radiation. Therefore, an extension of i ts absorption
wavelength range to the visible (Vis) is an important issue to improve the photocatalytic
performance of TiO 2 . Combining plasmonic metal nanoparticles (NPs) such as Au with TiO 2
is an outstanding strategy to improve the photocatalytic efficiency of semiconductor due tothe unique optical and electric properties of plasmonic metals . In particular, Au nanorods(NRs) with large aspect ratio can absorb the light in near-infrared (NIR) region by surface
plasmon resonance (SPR). The use of NIR light for the photocatalysis is large advantage
because the lights in NIR region (over 800 nm) were hardly used for the photocatalysis
under sunlight due to low energy of NIR light.
In this thesis, Au NPs and Au NRs were deposited on the photoactive meso porous
SiO 2 -TiO 2 template and the photocatalysis using SPR of Au NPs and Au NRs deposited inthe template was investigated. The effects of TiO 2 -Au interface, surface modification of thetemplate and SPR wavelength of Au NPs and Au NRs on the photocataly sis under Vis andNIR light irradiation were discussed.
In the first study, TiO 2 nanocrystal -containing mesoporous SiO 2 template werefabricated by sol-gel method and Au NPs or Au NRs were deposited in the as -formed
tubular mesopores by thermal reduction method. A morphology change of the Au NPs wasinvestigated when the content of TiO 2 in the template was varied. Au NRs with a lengthof 10 to 400 nm were obtained in the template containing 20 mol% TiO 2 and the length ofAu NRs was shortened with increasing in TiO 2 content because thermoexcited conduction
electrons are generated from TiO 2 and these generated electrons transfer to the Au ions toaccelerate their reduction. Also Au NPs in the template containing 20 mol% TiO 2 were depo
sited by UV radiation to the sample during heat treatment. UV radiation during Au
deposition in the template produced electrons photocatalytically and accelerated the Au
deposition rate, leading to the dominant formation of Au NPs. The rate constant s per unit
area for photobleaching of MB upon UV radiation by SiO 2-TiO2, Au NPs andAu NRs/SiO 2 -TiO 2 containing 20 mol% TiO 2 were evaluated. Bare SiO 2 -TiO 2 showed
3.24×10 -2 min -1 m -2 of rate constant per unit area, the Au NPs - and Au NRs-deposited
SiO 2 -TiO 2 possessed rate constants that were two and three times larger than that of thebare template. Vis irradiation of the prepared samples had no significant effect on theirphotocatalytic properties because the electronic contact between TiO 2 and Au was notformed by thermal reduction method.
In t he sec on d st ud y, A u NPs a nd Au NR s wer e de posi t ed i n Si O 2 -T i O 2 b yphotodeposition method with/without surface modification of the template b y
3-aminopropyltriethoxysilane (APTES) and Vis light-induced photocatalysis of preparedsamples was investigated. Without APTES, spherical Au NPs with a diameter of < 15 nm
formed dominantly at the outside of the mesoporous structure and showed the extinction at542 nm. The surface modification of the template with APTES prior to the deposition of Au
resulted in the formation of Au NRs with a diameter of ca. 5 nm and a length of 10 –15
nm in the tubular mesopores of the template and this sample showed two extinction peaks
at 528 and 700 nm. Au NPs-deposited sample worked well as a photocatalyst to bleach MB
under Vis light irradiation. Au NRs -deposited sample showed weak and abnor mal
photocatalytic activity, showing nonexponential curve in the photobleaching dynamics of MB
because APTES being on the surface of the template suppressed the adsorpti on of MB onto
the sample. Heat treatment to remove APTES from the sample led to the amelioration of thephotocatalytic activity. The formation of good electronic contact between Au NPs and TiO 2was found to be essential to the high Vis light -induced photoca talytic performance.
Finally, comparison of the photocatalytic activities of Au NPs/SiO 2 -TiO 2 with different
amounts of Au (0.3, 0.6, 1.2 and 1.8 mol% Au) and Au NRs/SiO 2 -TiO 2 was carried out
under UV, Vis and NIR light irradiation. Au NPs/SiO 2 -TiO 2 with an amount of 0.6 mol%Au showed the highest photocatalytic activity among the samples with different amount of Au under both UV and Vis light irradiation. The specific surface area of Au/SiO 2 –TiO 2decreased with increasing the amount of Au, resulting in the decrease of the photocatalytic activity of 1.2 and 1.8Au/SiO 2 -TiO 2. Au NRs/SiO 2 –TiO 2 showed higher photocatalytic activity
than Au NPs/SiO 2 -TiO 2 under both UV and Vis light irradiation. The reasons of the highphotocatalytic activity of Au/SiO 2 –TiO 2 were investigated by measuring the action spectra
and were considered to be the high specific surface area (353.2 m 2 g -1 ), the formation ofSchottky barrier between Au NPs and TiO 2 , the wider light absorption by SPR of Au NRs.