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The different ways of synthesis
In the laboratory, we develop synthesis techniques and protocols enabling us to prepare a very wide range of complex materials similar to the reactive materials present in the natural environment such as manganese oxides, iron oxides or clays. In order to be reactive towards contaminants, or more generally towards their environment, these materials generally have crystallochemical structures that are often disordered, irregular or present various types of structural defects. They also have a very large specific surface area and are therefore often present in the form of nanometric grains. Thus, in parallel with the protocols developed to synthesize well-crystallized materials, we adapt and refine our protocols in order to synthesize nano-materials by controlling the nature and density of the defects in their structure. These defects range from nanometric size to foliar load deficiency, through the presence of gaps or the substitution of one element by another one.
All these materials are mainly used in research projects on the themes of "Environment", "Georesources" and "Origin of Life" to determine the reaction mechanisms operating in the natural environment.
Colloidal synthesis
Syntheses of geomimetic compounds such as iron oxides or manganese oxides are mainly colloidal syntheses carried out in aqueous solution. They require the control of physico-chemical parameters such as pH, temperature, redox potential, concentration of precursor reagents or their addition rate. Varying these parameters influences the structure and properties of the synthesised compounds. All these parameters can be controlled using equipment such as peristaltic pumps, automatic Titration systems equipped with automatic burettes and electrodes (pH, redox, conductivity, specific electrode,...), thermostatically controlled baths...
The synthetic products are then characterised either by solid characterisation techniques or by chemical analysis techniques.
Synthesis in mild hydrothermal conditions
The synthesis of certain compounds such as todorokite or stevensite (respectively a manganese oxide and a smectite) requires so-called "mild hydrothermal" conditions. These syntheses are carried out in reactors equipped with a Teflon® liner, which allows pressure and temperature conditions of up to 40-50 bar and 210°C respectively. We have reactors of different volumes (23, 45 and 110ml) available in the laboratory.
The synthetic products are then characterised either by solid characterisation techniques or by chemical analysis techniques.
Synthesis under hydrothermal conditions High Pressure - High Temperature
Some phyllosilicates, such as hectorites (Nay Si8 Mg6-y Liy O20 (OH)4) or saponites (Nax Si8-x Alx Mg6 O20 (OH)4), are synthesized by the "sol-gel" method (which means "solution-gelling") from nitrate and carbonate salts in aqueous solution. This amorphous gel is then crystallised under hydrothermal conditions at temperatures and pressures of up to 400°C and 1000 bars respectively.
These hydrothermal reactions are carried out either in a 1 to 2 ml gold capsule placed in a cold seal autoclave, or in a larger volume reactor (40 ml) placed in a furnace with controlled pressure and temperature.
The synthetic products are then characterised either by solid characterisation techniques or by chemical analysis techniques.
These compounds are used in research projects to study the dynamics of water in soils or the storage of gases in soils.
