Exploring the structure of pure germanophospate glasses with different concentrations probed by magic angle spinning NMR spectroscopy

Phosphate-based glasses such as pure germanophosphate can be achieved at moderately low temperature by means of affordable chemical substances. Nowadays, they become more stimulating because they can be easily doped with alkali, transition metal ions, and rare earth oxides to afford the anticipated physical and/or chemical features for nanoscience applications. Herein, we report an experimental study dealing with the structure of pure germanophosphate glass samples of ${\text{GeO}}_2$ prepared with different concentrations ranging from 20 up to 70 mole%. ³¹ P magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy has been employed to characterize the co-formed glasses by two different glass-forming oxides. The components of the phosphate species ( $Q^n$ ) in each sample were determined by analyzing the MAS NMR spectra. Interestingly, ³¹ P MAS NMR spectrum for each sample was found to be characteristic powder patterns of the middle units Q² . Q² unit found herein has one oxygen atom bonded towards one germanium atom (non-bridging) and the other two oxygens are bonding towards two phosphorus atoms (bridging) of phosphate group (PO₄ ). The results show that Q² split into two units, Q² I and Q² II, due to different shielding of the phosphorus nucleus provided by the next nearest neighbor atoms. The chemical shift is interpreted in terms of the structure of each building unit of the phosphate group. The results obtained herein shed light on the way how to explore the revealed structure of the prepared glasses for the development of supported catalysts. Indeed, owing to their high chemical/thermal stability, the co-formed germanophosphate glasses obtained may prove as useful substrates for potential nanocatalysts.