Versatile biomimetic dendrimer templates used in the formation of TiO2 and GeO2

Abstract

Biomimetic synthesis is emerging as an advantageous alternative to the harsh synthetic conditions traditionally used in metal oxide syntheses techniques. Silaffins, proteins from the C. fusiformis diatom, form silica in an aqueous environment under benign conditions. Amine terminated PAMAM and PPI dendrimers are effective mimics of silaffins and other silica precipitating polyamines. We have expanded the scope of dendrimer mediated metal oxide formation to include titanium dioxide, a photocatalyst, and germanium dioxide, a blue photoluminescent material. The nanoparticles were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (IR), and X-ray diffraction patterns (XRD). A variable temperature XRD analysis of TiO₂ nanoparticles was conducted to study the transition from anatase to rutile. TiO₂ nanoparticles synthesized in phosphate buffer showed a 200 °C decrease in the anatase to rutile transition temperature relative to TiO₂ templated in water. XRD analysis of GeO₂ nanoparticles in either water or phosphate buffer reveal crystalline α-phase germanium oxide. To our knowledge, this is the first report of the synthesis of crystalline GeO₂ under ambient conditions.