Electronic Properties of One-Dimensional Titanate Nanofilaments and their Dye-Sensitization Behavior

A.D. Walter, G.R. Schwenk, J. Cope, K. Sudhakar, M.Q. Hassig, L. Ferrer, A. Mininni, M.W. Barsoum
Drexel University,
United States

Keywords: one-dimensional, titanate, nanofilaments, dye-sensitization, band structure

Summary:

Dye-sensitized titania and titanate materials are popular for multiple applications including solar and photoelectrochemical cells. A first proof of sensitization is by degrading the sensitizing dye in an aqueous suspension, a phenomenon called self-sensitization. This is widely studied under the guise of water treatment, primarily in textile waste remediation. A novel lepidocrocite-structured layered titanate has exhibited self-sensitization to a level not previously reported. This material is comprised of one-dimensional base units of just 3x2 TiO6 octahedral units that stitch themselves together into a variety of different morphologies. This work is focused on the colloidal product of these one-dimensional lepidocrocite titanate nanofilaments, or 1DLs. When the colloidal 1DLs are added to a cationic dye solution, they flocculate – similar to many polymers used in water treatment – and crash out of suspension. During this flocculation, they adsorb over 1.8 mol/kg of the common model dyes crystal violet and rhodamine 6G. In some more recent, unpublished, work, malachite green, a dye widely used in aquaculture, was also explored and resulted in similar maximum uptake. The dye sensitization behavior of all three dyes is excessively high, exhibiting decolorization of more than 50% in 30 minutes, at a 1DL to dye mass ratio of just 1 to 1. At these conditions, P25, the standard titania material used in photocatalyst experiments, exhibits no decolorization activity. These published results will be discussed in detail, including more fundamental work with regards to the electronic band structure of 1DLs and their optical properties. There will also be a commentary on the potential pathways for these fascinating materials to expand their reach into work into more traditional applications of dye-sensitization, like solar cells and photoelectrochemical cells for water splitting. Additionally, due to their technological novelty, the structure and optical properties of 1DLs will be introduced. Both experimental and DFT-calculated band structures will be presented. An emphasis will be placed on the revolutionary fabrication process of 1DLs, that allows for simple scale-up.