TiO2 powders synthesized by pressurized fluid extraction and supercritical drying: Effect of water and methanol on structural properties and purity

Pressurized water extraction followed by sub/supercritical methanol drying was used for synthesis of TiO2 from gels prepared by sol–gel technique using Triton X-114 like template. It was proved that pressurized water causes titania crystallization. Subsequent sub/supercritical methanol drying is responsible for total elimination of the rest of organic phase originating from the template. The impact of temperature and pressure modifications on titania purity was more essential for pressurized water extraction. The specific surface area significantly increases with removal of the residual organic phase. Anatase was a dominant crystalline phase. The fraction of minor brookite was in the range 20–30 wt.%. In situ XRD showed stability of titania crystallites size up to 300 °C and the presence of brookite crystallites even up to 600 °C. The correlation between Raman FWHM and XRD crystallite size was not influenced by the presence of organic phase and was more sensitive for anatase Eg band 647 cm−1.

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► A new technique to prepare well-defined excellently pure nanocrystalline titania.
► Pressurized water causes titania crystallization.
► Subsequent sub/supercritical methanol drying causes total removal of organic phase.
► The specific surface area significantly increases by total removal of organic phase.
► Brookite is present in titania up to 600 °C due to small crystallite size.