Bioinspired mineralisation: macromolecule mediated synthesis of amorphous germania structures

The unique optical properties of germanium dioxide or germania (GeO2), and in particular when compared with other glasses such as silicate glasses, have attracted the attention of scientists and made germania based materials highly suitable for optoelectronic applications. Germanium is known to resemble silicon in some of its chemical properties (in vitro) and biochemical properties (in vivo). The recent findings on the importance of the role of the (bio)macromolecules in (bio)mineralisation has led us to investigate the role of synthetic macromolecules in facilitating the formation of germania particles for the first time. One novelty is that the process described herein was carried out under ambient conditions and at neutral pH. The macromolecules used were poly (allylamine hydrochloride) (PAH) and poly-l-lysine (PLL), and it should be noted that both are cationically charged at neutral pH. Either germanium (IV) ethoxide or germanium (IV) isopropoxide were used as the germania precursors. The products were characterised by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD). Well-defined spherical germania particles were seen by electron microscopy and they were shown to be amorphous by XRD. In addition, based on Energy Dispersive Spectroscopy (EDS) observations, it was proposed that the facilitating macromolecules may be incorporated into the germania. Furthermore, when the reaction mixture was subjected to external shear, the formation of elongated rod-like germania structures was successfully achieved. It is proposed that the macromolecules act as catalyst/scaffold/template in a similar fashion to that described in the literature for the formation of (bio)silica as facilitated by (bio)macromolecules. This novel process is of importance for both the design of new materials based on germania and also silica-germania hybrids. These materials have a variety of potential commercial applications, an example being their use in optical fibre technologies.