Enhanced photocatalytic degradation by diatom templated mixed phase titania nanostructure

Diatom frustules are abundantly available, environmentally non-toxic natural structures that can enhance photocatalytic activity when templated with titania nanostructures. Dye molecules such as of Azo dye, when allowed to occupy spaces available within a porous diatom frustule templated titania nanostructure, get greater exposure to light photons because diatom frustules not only can collect and transmit light very efficiently through their structure but also naturally arranges the dye molecules within the structure in such a way that there is a lot of optical paths for the light photons to move within the structure and thereby exposing more dye molecules to the light. Moreover, these structures also transmit UV light, unlike ordinary glass structures and hence, enrich the degradation of the dye molecules. This paper reports the observation of breaking of Ti-O anatase bonds at 800 degrees C to a considerable extent and consequent formation of new Ti-O rutile bonds at that temperature, generating oxygen vacancies and defect states which results in lowering the band gap of diatom templated titania nanostructures. As such, diatom calcined at 800 degrees C with titania (DT800), containing both anatase and rutile phase (mixed phase) of nano-sized titania, showed advantageous visible light range photocatalytic activity and enhanced separation efficiency of the photo generated electron-hole pairs compared to diatom calcined at 500 degrees C with titania (DT500), which contain only anatase phase of nano-sized titania. (C) 2017 Elsevier B.V. All rights reserved.