scCO2-based synthesis of semi-crystalline TiO2 nanoparticles: A rapid and direct strategy

This work describes a rapid and direct synthesis strategy for semi-crystalline TiO2 nanoparticles by scCO(2) antisolvent expansion of sol-gel precursor. The scCO(2)-based nanoparticles were produced by the hydrolysis reaction of titanium (IV) isopropoxide in an aqueous medium. The successful synthesis of these nanoparticles was associated to the formation of a scCO(2)-induced one-phase system, which allowed both a rapid reaction of the precursor and an efficient drying (by expansion onto scCO(2)) of the product. The nanoparticles showed a well-marked amorphous-to-crystalline transition as submitted to thermocycling. The BET analysis of TiO2 nanoparticles showed a surface area of 418.5 m(2) g(-1) and the DLS curve indicated an average size of 316.7 +/- 2.7 nm. The use of scCO(2) expansion technology as a reaction medium allowed the synthesis of a nanomaterial with a large surface area, making it attractive for use in adsorption process. The obtained material is free of organic solvents, catalysts or surfactants, and does not require further purification. This study offers not only an environmentally friendly product, but also a simple approach which does not need particular skills. (C) 2014 Elsevier B.V. All rights reserved.