Porous Anatase Nanoparticles with High Specific Surface Area Prepared by Miniemulsion Technique

A simple template-free approach to generate spherical porous anatase nanoparticles by combining the sol-gel process with the inverse miniemulsion technique is reported. These as-synthesized particles of about 200 nm in diameter consist of aggregated small anatase crystallites of several nanometers, thus leading to a high specific surface area of more than 300 m ·g, even after calcination at 400 °C. The only employed surfactant is a block copolymer (P(E/B-b-EO)), which stabilizes the aqueous droplets with the water-soluble precursor bis(2-hydroxyethyl)titanate (EGMT) in the organic phase but also leads to aggregation and pore formation inside the particles. The lower relative rates of hydrolysis and condensation compared to the commonly used titanium alkoxides allow convenient handling in miniemulsion. Here we report the effects of synthesis conditions, such as the amount of surfactant, the composition of the dispersed phase, and the reaction and calcination temperature, on the particle size, porosity, crystallite size, crystallite phase, and specific surface area of the obtained nanoparticulate material. After removing the continuous phase, the obtained powders were characterized before and after calcination by transmission (TEM) and scanning electron microscopy (SEM), X-ray diffraction (XRD), and nitrogen sorption (BET).