TiO2 Synthesis Inspired by Biomineralization: Control of Morphology, Crystal Phase, and Light-Use Efficiency in a Single Process

Abstract

Hydroxyapatite is mineralized along the long axis of collagen fiber during osteogenesis. Mimicking such biomineralization has great potential to control inorganic structures and is fast becoming an important next-generation inorganic synthesis method. Inorganic matter synthesized by biomineralization can have beautiful and functional structures that cannot be created artificially. In this study, we applied biomineralization to the synthesis of the only photocatalyst in practical use today, titanium dioxide (TiO₂). The photocatalytic activity of TiO₂ mainly relates to three properties: morphology, crystal phase, and light-use efficiency. To optimize TiO₂ morphology, we used a simple sequential peptide as an organic template. TiO₂ mineralized by a β-sheet peptide nanofiber template forms fiber-like shapes that are not observed for mineralization by peptides in the shape of random coils. To optimize TiO₂ crystal phase, we mineralized TiO₂ with the template at 400 °C to transform it into the rutile phase and at 700 °C to transform it into a mixed phase of anatase and rutile. To optimize light-use efficiency, we introduced nitrogen atoms of the peptide into the TiO₂ structure as doped elemental material during sintering. Thus, this biomineralization method enables control of inorganic morphology, crystal phase, and light-use efficiency in a single process.