Peptide-templated biomineralization of titanium dioxide toward improved light absorption and photodegradation activity†

The mineralization of TiO₂ has been previously investigated by controlling the morphology and crystal phase of TiO₂ using several organic templates, but the relationship between the molecular structure of the template and the functionality of the mineralized TiO₂ has not been reported. In this study, we investigated the influence and photodegradation activity of the TiO₂ mineralized by different functional groups on the peptide template surface (i.e., Ac-(Val-Lys-Val-Lys-Val-Glu)₃-CONH₂: KE, Ac-(Val-Lys-Val-Lys-Val-Ser)₃-CONH₂: KS, and Ac-(Val-Lys-Val-Lys-Val-Tyr)₃-CONH₂: KY). The KE–TiO₂ and KS–TiO₂ hybrids exhibited absorption only in the UV region (<380 nm), whereas the KY–TiO₂ hybrid absorbed in a wider wavelength region that stretched into the visible spectrum (<500 nm). In addition, the KS–TiO₂ hybrid showed a higher self-photosensitized degradation activity than the other systems owing to an efficient separation between electrons and holes, whereas the KY–TiO₂ hybrid showed not only a reduction in self-photosensitized degradation activity due to the recombination between the methylene blue⁺˙ radical cation (MB⁺˙) and the injected electron, but also an increase in photocatalytic activity under UV or visible light irradiation. Our findings show that biomineralizing TiO₂ presents an excellent and highly attractive approach to further functionalizing and optimizing TiO₂via an inexpensive and facile process, which will find use in all research fields that utilize TiO₂ for such purposes.