Reactive precipitation of titanium dioxide particles in supercritical CO2 by SAS technique with an ionic liquid as adjuvant

Mesoporous titanium dioxide particles (TiO2) were prepared by reactive precipitation in the supercritical anti-solvent (SAS) technique using carbon dioxide in an ambient saturated with water in the presence of the ionic liquid (IL) 1-methyl-3-octylimidazolium bis[trifluoromethylsulfonyl] imide, [C8mim][NTf2]. All experiments of reactive precipitation with SAS were conducted at 40 °C, with a pressure of 8.0 MPa, a CO2 liquid flow rate of 20 mL min–1, and a solution flow rate of 2 mL min–1. Additionally, the influence of the molar ratio of titanium(IV) isopropoxide/isopropanol and ionic liquid/titanium(IV) isopropoxide was investigated. The particles were characterized by X-ray powder diffraction, thermogravimetric analysis, N2 adsorption-desorption analysis (BET surface area), and field-emission gun scanning electron microscopy. Results indicate the formation of anatase and brookite crystalline phases after calcination at 450 °C for 2 h. Besides, the peaks related to the brookite phase were more intense on samples synthesized using the IL. The synthesized TiO2 particles have suitable structural properties, such as high surface area, controlled porosity, narrow pore size distribution (lower than 6 nm), and high thermal stability. Further, particles with spherical morphology are produced, while those synthesized with the IL present smooth surfaces. The use of the IL decreases the particle size from 1.12 ± 0.78 μm (TiO2 without IL) to particles in the range from 0.32 ± 0.13 to 0.66 ± 0.44 μm. Furthermore, the higher the precursor/alcohol ratio, the larger the particle size, thus demonstrating that the particle size also depends on the precursor/alcohol ratio.