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Protein-Enabled Layer-by-Layer Syntheses of Aligned, Porous-Wall, High-Aspect-Ratio TiO2 Nanotube Arrays

Authors

  • John D. Berrigan,

    1. School of Materials Science and Engineering and Air Force Center of Excellence on Bio-nano-enabled Inorganic/Organic Nanocomposites and Improved Cognition (BIONIC), Georgia Institute of Technology, 771 Ferst Drive, Atlanta, Georgia 30332–0400, USA
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  • Tae-Sik Kang,

    1. Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, 45433–7702, USA
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  • Ye Cai,

    1. School of Materials Science and Engineering and Air Force Center of Excellence on Bio-nano-enabled Inorganic/Organic Nanocomposites and Improved Cognition (BIONIC), Georgia Institute of Technology, 771 Ferst Drive, Atlanta, Georgia 30332–0400, USA
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  • James R. Deneault,

    1. Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, 45433–7702, USA
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  • Michael F. Durstock,

    1. Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, 45433–7702, USA
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  • Kenneth H. Sandhage

    Corresponding author
    1. School of Materials Science and Engineering and Air Force Center of Excellence on Bio-nano-enabled Inorganic/Organic Nanocomposites and Improved Cognition (BIONIC), Georgia Institute of Technology, 771 Ferst Drive, Atlanta, Georgia 30332–0400, USA
    • School of Materials Science and Engineering and Air Force Center of Excellence on Bio-nano-enabled Inorganic/Organic Nanocomposites and Improved Cognition (BIONIC), Georgia Institute of Technology, 771 Ferst Drive, Atlanta, Georgia 30332–0400, USA.
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Abstract

An aqueous, protein-enabled (biomimetic), layer-by-layer titania deposition process is developed, for the first time, to convert aligned-nanochannel templates into high-aspect-ratio, aligned nanotube arrays with thin (34 nm) walls composed of co-continuous networks of pores and titania nanocrystals (15 nm ave. size). Alumina templates with aligned open nanochannels are exposed in an alternating fashion to aqueous protamine-bearing and titania precursor-bearing (Ti(IV) bis-ammonium-lactato-dihydroxide, TiBALDH) solutions. The ability of protamine to bind to alumina and titania, and to induce the formation of a Ti–O-bearing coating upon exposure to the TiBALDH precursor, enables the layer-by-layer deposition of a conformal protamine/Ti–O-bearing coating on the nanochannel surfaces within the porous alumina template. Subsequent protamine pyrolysis yields coatings composed of co-continuous networks of pores and titania nanoparticles. Selective dissolution of the underlying alumina template through the porous coating then yields freestanding, aligned, porous-wall titania nanotube arrays. The interconnected pores within the nanotube walls allow enhanced loading of functional molecules (such as a Ru-based N719 dye), whereas the interconnected titania nanoparticles enable the high-aspect-ratio, aligned nanotube arrays to be used as electrodes (as demonstrated for dye-sensitized solar cells with power conversion efficiencies of 5.2 ± 0.4%).

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