(199a) Benign Silica and Germania Synthesis: From Monodisperse Nanoparticles and Nanocrystals to Porous Inorganic Hollow Shells and Thin Films

Drawing motivation from ubiquitous biomineralized silica structures in nature, we recently identified the formation of stable, highly monodisperse silica nanoparticles in aqueous amino acid solutions.^[1,2] The novelty of the synthesis derives from its simplicity and benign nature (i.e., more neutral pH), where hydrolysis of a silica source is accomplished in an aqueous solution of L-Lysine and a range of handles exist for tuning particle size (ca. 5-25 nm). Spurred by an interest to explore the influence of biomolecules on other oxide systems, we have extended the amino acid-mediated synthesis techniques to that of germania,^[3] an oxide bearing interesting reactive and optical properties. Here, we will first discuss the facile synthesis of nanometer-sized germania crystals and amorphous germania nanoparticles (ca. 1 nm) through hydrolysis of germanium tetraethoxide and subsequent condensation of germania in both pure water and aqueous lysine solutions. We will analyze similarities between the lysine-mediated germania and silica synthesis as related to the transition from germinate species to nanoparticles in solution. In addition, we will highlight the remarkable room temperature aqueous crystallization of germania, and will discuss the influence of lysine, nanoparticles, and germania concentration on the onset of crystallization and the resulting crystal size, morphology, and monodispersity.

In general, the room temperature and near-neutral conditions for nanoparticle formation and crystallization, especially in the presence of the basic amino acid lysine, make both the silica and germania systems attractive for benign materials applications. As such, we will describe techniques for successful assembly of the nanoparticles into nanoparticle-crystals and ordered multi- and monolayer coatings, where micro and mesoporosity imparted by the interstitial particle spacing can be engineered by fine control of particle size. We will also describe how materials properties of both metal oxide systems (i.e., charge, stability, solubility) can be leveraged individually and simultaneously for novel and benign (i.e., temperature, pH) synthesis of metal oxide core-shell structures, highly monodisperse hollow porous shells, and novel nanoparticulate and structured thin films.

References

1. Davis, Snyder, Krohn, Tsapatsis, Chemistry of Materials, 2006, 18(25), 5814-5816.

2. Snyder, Lee, Davis, Scriven, Tsapatsis, Langmuir, 2007, 23(20), 9924-9928.

3. Davis, Snyder, Tsapatsis, Langmuir, 2007, 23(25), 12469-12472.