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Nano titanium dioxide can be prepared via several different methods. The following includes two of these methods: the sol-gel preparation method and the hydrothermal method.
1. Sol-Gel Method:
- Initial solution preparation: Solutions of titanium isopropoxide and ethanol are prepared first. The titanium isopropoxide solution functions as the precursor.
- Gelation process: The previously prepared solution is allowed to hydrolyze and condense at room temperature in a controlled humidity environment. This stage forms a wet, gel-like substance.
- Aging process: The wet gel is sealed and stored at a constant temperature, during which time the gel shrinks due to the self-evaporation of the solvent and the pores of the gel begin to form.
- Drying: The shrunken gel is then dried either in the open air or under supercritical conditions to form a dry gel.
- Calcination: The dry gel is heat treated, or calcined, at high temperatures, a process that results in a regulatory rearrangement of the porous el network into nano titanium dioxide.
2. Hydrothermal Synthesis Method:
- Titanium swelling agent preparation: Titanium swelling agents are prepared by dissolving a titanium source (like titanium trichloride or titanium tetrachloride) in water to produce a titanium-rich solution.
- Hydrated metallurgical process: The swelling agent is then reacted with a strong alkali (like NaOH or NH3·H2O) in an excess of water at high temperatures and pressures. A white precipitate of titanium hydrate forms.
- Acid washing: The resulting white precipitate is filtered, washed with an acid solution, and re-filtered.
- Oven drying: The remaining precipitate is dried in an oven at a moderate temperature (around 80°C).
- Calcination: Finally, the dried precipitate is calcined at a high temperature to obtain nano titanium dioxide.
All procedures need to follow safety protocols and be carried out in a lab setting by trained professionals due to the use of harmful chemicals and high temperatures.
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