Hydrothermal Synthesis
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"Hydrothermal" is a geologic origin, it makes use of high pressure to crystallize the materials in the solvents. The solvent can be aqueous (e.g., DI water) or non-aqueous (e.g., organic solvents). Precursors must be able to dissolve into the solvent. For oxygen-sensitive materials (e.g., VS2), the synthesis is best using non-aqueous solvents, albeit it is environmentally unfriendly. The reaction temperature is typically less than 200oC and the reaction hours may range between a few 10 minutes to days.
(1) Prepare the precursor solution in a beaker. Magnetically stir it using a hotplate until a homogeneous solution is obtained. Add the precursor solution into the PTFE liner. Ensure that the feeding coefficient is less than 0.8 (filled up less than 80% of the volume to avoid overpressure).
(2) If you want to grow the materials on a substrate (carbon fiber paper or Ni foam) you can choose to immerse it into the solutions. Otherwise, assemble the PTFE liner with its covers. Transfer it into the autoclave. Then, tighten the lid of the autoclave.
(3) Afterward, put the autoclave into an oven for the reaction. The oven temperature was raised to the desired reaction temperature. (The maximum temperature cannot exceed 200 oC to avoid overpressure).
(4) After the reaction is complete, wait for the temperature drops to room temperature. Open the autoclave lid and take out the PTFE liner. You may need to collect your sample via centrifuge and freeze drying.
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