Functionalisation of the three dimensional porous structure of diatom frustules for use in DSSC's and other applications

[Truncated abstract] Diatomite (diatom shells/frustules) has gathered considerable research interest in recent years as more groups attempt to harness the three dimensional porous architecture of the diatom frustules for technological applications. To this end, a binding method was developed that was shown to effectively coat the frustules with magnetite, silver and titania, for eventual incorporation into dye sensitised solar cells (DSSC’s). Processing of the diatomite via plasma treatment resulted in highly reactive surface that proved accommodating for the immobilisation of the metal and metal oxide nanoparticles. Of the three materials the titania coated frustules was the most directly applicable to DSSC’s, and was used as the photoanode in lieu of titania nanoparticles.

The binding technique is centred around a plasma pre-treatment of the diatomite followed by slow reduction, oxidation or hydrolysis depending on the material. Initially titania was bound to the diatom frustules using two different linking agents, citric acid and poly-4-vinylpyridine. Each linking agent had a different effect, with citric acid preferentially forming a titania film over the surface of the frustules while the use of poly-4-vinylpyridine resulted in nanoparticles of 90-100 nm. The technique was further developed for the attachment of the silver and magnetite nanoparticles to the frustule surfaces. In these cases no linking agents were required, the metal and metal oxide nanoparticles could be bound directly to the surface. The magnetite technique resulted in a consistent and complete coating of the frustules without affecting its architecture. This material showed a strong reaction to external magnetic fields and through analysis with the superconducting quantum interference device (SQuID) it was established to be superparamagnetic. Iron oxides are well known for their effectiveness in water treatment, and as diatomite is commonly used in high quality filters, the material was tested for its selected ion removal properties. Phosphate uptake was effective with more than a 9 fold improvement in removal compared to uncoated frustules. The synthesis of the silver coated frustules although using the same method of plasma pre-treatment and slow reduction, utilised a green synthetic route. Using glucose as a reducing agent it was possible to grow and bind silver nanoparticles between 10 and 20 nm directly onto the surface of diatom frustules.