(84e) Supercritical Solvothermal Flow Synthesis of Advanced Nanostructured Materials

The specific properties of supercritical fluids are exploited for more than 35 years to develop breakthrough technologies, especially in the field of the preparation of advanced materials, from organics to inorganics through carbon-based materials. This technology of material processing is continuous, fast, sustainable and scalable and gives access to high quality nanostructured materials with unique physico-chemical properties, meaning which can not be obtained with other synthetic methods.

In the last 3 years, we have opened a new field for the supercritical solvothermal flow synthesis: the continuous production of synthetic phyllosilicates and ionosilicates. The proof of concept was made with the synthesis in few tens of seconds of talc in a continuous millifluidic process. Very interestingly, this synthetic talc exhibits unique properties. Adding ethanol to water, meaning switching from supercritical hydrothermal to supercritical solvothermal conditions, brought unexpected results. Depending on the water/ethanol ratio of the solvent, three different minerals adopting an octahedral brucitic sheet can be obtained: i) without Si-tetrahedral sheet (O), ii) associated with one Si-tetrahedral sheet (T-O) or iii) intercalated between two Si-tetrahedral sheets (T-O-T). The supercritical hydrothermal flow synthesis has also been extended to the ultrafast preparation of inominerals, the xonotlite and the tobermorite, two calcium silicates with interesting properties for the cimentitious industry. Especially, it is important to underline that the tobermorite is obtained under thermodynamically metastable conditions.

The benefits of the sub- and supercritical continuous solvothermal route include not only better performances for advanced applications but also environmental issues associated with the synthesis process. This will be emphasized with the studies performed using LCA approaches.