Mesoporous TiO<inf>2</inf> films with regularly aligned slit-like nanovoids

Hirokatsu Miyata, Yuta Fukushima, Yosuke Kanno, Saeko Hayase, Shintaro Hara, Masatoshi Watanabe, Shin Kitamura, Masahiko Takahashi, Kazuyuki Kuroda

    Research output: Contribution to journalArticle

    8 Citations (Scopus)

    Abstract

    Novel mesoporous TiO<inf>2</inf> films with regularly aligned slit-like nanovoids are prepared through structural transformation from a mesostructured TiO<inf>2</inf> film with honeycomb-packed aligned cylindrical micelles by pyrolytic removal of the micelle template. The transformation takes place through interconnection of the TiO<inf>2</inf> walls of the framework in the thickness direction by a heat-induced shrinkage and eventual collapse of the original channel structure. For the formation of this new structure, the preparation of a mesostructured titania film with cylindrical micelles aligned entirely in the plane of the film over the whole thickness is indispensable. This is achieved by coating a substrate, on which a rubbing-treated polyimide layer is formed, with a precursor solution containing two nonionic surfactants, Brij56 and P123. In the mixed surfactant system, Brij56 works as an alignment-controlling agent through selective and directional adsorption on the anisotropic polymer surface. On the other hand, P123 suppresses the formation of a surface layer without controlled in-plane alignment, which has been inevitable when Brij56 is used alone. This is caused by the retarded condensation of the TiO<inf>2</inf> precursors due to increased coordination of oxyethylene moieties on titanium. P123 also increases the wall thickness of the framework, which also contributes to the formation of this mesoporous TiO<inf>2</inf> film with oriented regular slit-like voids. The structural transformation takes place in a relatively low temperature range lower than 300 °C, which shows that the driving force is not crystallization. The mesoporous TiO<inf>2</inf> films with aligned slit-like voids show optical anisotropy, birefringence, with a Δn value of ∼0.023 reflecting the structural anisotropy of the film. Calcination of the aligned mesostructured TiO<inf>2</inf> film at 450 °C induces crystallization of TiO<inf>2</inf>, which deteriorates the meso-scale structural regularity by interconnection of the TiO<inf>2</inf> walls. However, the partial retention of the regular structure is confirmed in the vicinity of the surface, which allows the retention of the optical anisotropy. The novel mesoporous TiO<inf>2</inf> films in this paper have potential for optical applications by combining their unique anisotropic mesostructure, which enhances the accessibility to the inner surface, with various properties of TiO<inf>2</inf> such as high refractive index and photocatalytic activity. This journal is

    Original languageEnglish
    Pages (from-to)3869-3875
    Number of pages7
    JournalJournal of Materials Chemistry C
    Volume3
    Issue number16
    DOIs
    Publication statusPublished - 2015 Apr 28

    Fingerprint

    Micelles
    Optical anisotropy
    Crystallization
    Titanium
    Nonionic surfactants
    Birefringence
    Polyimides
    Surface-Active Agents
    Calcination
    Condensation
    Refractive index
    Polymers
    Anisotropy
    Surface active agents
    Adsorption
    Coatings
    Substrates
    Temperature

    ASJC Scopus subject areas

    • Chemistry(all)
    • Materials Chemistry

    Cite this

    Mesoporous TiO<inf>2</inf> films with regularly aligned slit-like nanovoids. / Miyata, Hirokatsu; Fukushima, Yuta; Kanno, Yosuke; Hayase, Saeko; Hara, Shintaro; Watanabe, Masatoshi; Kitamura, Shin; Takahashi, Masahiko; Kuroda, Kazuyuki.

    In: Journal of Materials Chemistry C, Vol. 3, No. 16, 28.04.2015, p. 3869-3875.

    Research output: Contribution to journalArticle

    Miyata, H, Fukushima, Y, Kanno, Y, Hayase, S, Hara, S, Watanabe, M, Kitamura, S, Takahashi, M & Kuroda, K 2015, 'Mesoporous TiO<inf>2</inf> films with regularly aligned slit-like nanovoids', Journal of Materials Chemistry C, vol. 3, no. 16, pp. 3869-3875. https://doi.org/10.1039/c4tc02932a
    Miyata H, Fukushima Y, Kanno Y, Hayase S, Hara S, Watanabe M et al. Mesoporous TiO<inf>2</inf> films with regularly aligned slit-like nanovoids. Journal of Materials Chemistry C. 2015 Apr 28;3(16):3869-3875. https://doi.org/10.1039/c4tc02932a
    Miyata, Hirokatsu ; Fukushima, Yuta ; Kanno, Yosuke ; Hayase, Saeko ; Hara, Shintaro ; Watanabe, Masatoshi ; Kitamura, Shin ; Takahashi, Masahiko ; Kuroda, Kazuyuki. / Mesoporous TiO<inf>2</inf> films with regularly aligned slit-like nanovoids. In: Journal of Materials Chemistry C. 2015 ; Vol. 3, No. 16. pp. 3869-3875.
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    abstract = "Novel mesoporous TiO2 films with regularly aligned slit-like nanovoids are prepared through structural transformation from a mesostructured TiO2 film with honeycomb-packed aligned cylindrical micelles by pyrolytic removal of the micelle template. The transformation takes place through interconnection of the TiO2 walls of the framework in the thickness direction by a heat-induced shrinkage and eventual collapse of the original channel structure. For the formation of this new structure, the preparation of a mesostructured titania film with cylindrical micelles aligned entirely in the plane of the film over the whole thickness is indispensable. This is achieved by coating a substrate, on which a rubbing-treated polyimide layer is formed, with a precursor solution containing two nonionic surfactants, Brij56 and P123. In the mixed surfactant system, Brij56 works as an alignment-controlling agent through selective and directional adsorption on the anisotropic polymer surface. On the other hand, P123 suppresses the formation of a surface layer without controlled in-plane alignment, which has been inevitable when Brij56 is used alone. This is caused by the retarded condensation of the TiO2 precursors due to increased coordination of oxyethylene moieties on titanium. P123 also increases the wall thickness of the framework, which also contributes to the formation of this mesoporous TiO2 film with oriented regular slit-like voids. The structural transformation takes place in a relatively low temperature range lower than 300 °C, which shows that the driving force is not crystallization. The mesoporous TiO2 films with aligned slit-like voids show optical anisotropy, birefringence, with a Δn value of ∼0.023 reflecting the structural anisotropy of the film. Calcination of the aligned mesostructured TiO2 film at 450 °C induces crystallization of TiO2, which deteriorates the meso-scale structural regularity by interconnection of the TiO2 walls. However, the partial retention of the regular structure is confirmed in the vicinity of the surface, which allows the retention of the optical anisotropy. The novel mesoporous TiO2 films in this paper have potential for optical applications by combining their unique anisotropic mesostructure, which enhances the accessibility to the inner surface, with various properties of TiO2 such as high refractive index and photocatalytic activity. This journal is",
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