Nanostructured Inorganic Materials in a Marine Environment
Résumé de la communication de Jacques LIVAGE (Collège de France, Paris, France) donnée à l’occasion du séminaire Les constructions en milieu marin / Constructions in marine environment du 14 au 19 mars 2016
Photosynthetic micro-algae from the phytoplankton play a major role in ecology. They are responsible for the production of 50% of oxygen on earth. Moreover they build very nice nanostructured solid shells made of CaCO3 for coccolithophorides and SiO2 for diatoms. Inorganic chemists are trying to understand how they build such nice solid shells and then to mimick them to make advanced bio-inspired glasses and ceramics!
Calcite coccospheres are formed via the self-assembly of CaCO3 nanocrystals. Organic molecules such as polysaccharides play a major role in this process. They prevent the growth of nanocrystals and then lead to their oriented assembly. Taking example of these micro-algae, chemists have developed new syntheses in which Double Hydrophylic Block Copolymers (DHBC) lead to the formation of nanostructured mesocrystals. These mesocrystals exhibit interesting new properties. Lithium batteries based on nano-urchin vanadium oxides for instance have been shown to exhibit much higher capacities.
Silica frustules made by diatoms are formed via a polymerization process based on the polycondensation of solute silicic acid Si(OH)4 molecules. This sol-called ‘sol-gel process’ has been extensively developed during the past decades for making glasses and ceramics. Shaped materials such as nanoparticles, fibres or coatings, can be obtained at low temperature directly from the solution. Moreover, the mild conditions associated with this ‘chimie douce’ are compatible with fragile organic molecules. It becomes then possible to make hybrid nanocomposite materials in which organic and inorganic phases are mixed at a molecular scale. Even bio-molecules such as enzymes have been trapped within oxide matrices. Silica nanoparticles for instance can be used to bring drugs inside tumor cells allowing the development of nanomedicine.
The example of diatoms suggests that micro-organisms can live inside a glass box. Living materials are then obtained in which live cells (bacteria, fungi, yeasts, protists…) are trapped within inorganic matrices. They retain their metabolic activity for several months and lead to the development of bio-sensors and bio-reactors that have been used for the depollution of water!