1H, 29Si and 27Al NMR study of the destabilization process of a paracrystalline opal from Mexico

This is the first NMR study of the destabilization through whitening of paracrystalline opal-CT (SiO2, nH2O). The aim of this study is to understand the process leading to the degradation, particularly any changes in the structure and bonding of this material. 29Si and 27Al NMR signals are not significantly modified. In contrast, using for the first time 1H as a probe in opal, we show that a comprehensive understanding can be obtained on both the local structure of the opal-CT and the destabilization process. Thus, we propose the latter is related to some changes in 1H speciation (loss of strongly ‘bound’ water and appearance of new species) which induce structural reorganizations on the surface and in the rim of the silica nanograins constituting opal-CT.