Preparation and characterization of surface silanized TiO₂ nanoparticles under compressed CO₂: Reaction kinetics

The feasibility of the use of compressed carbon dioxide (CO2) as a solvent for the coating of titanium dioxide (TiO2) nanoparticles with octyltriethoxysilane was tested in this work. These studies were focused on investigating the influence of the pressure, temperature, and reaction time on the process kinetics as well as on the resulting materials properties. A fundamental kinetic study was performed for the more slow process occurring under near-critical conditions to obtain useful information about the silanization mechanism. Self-assembled silane monolayers were formed very fast (15 min) under supercritical CO2 with grafting densities of ca. 2.8-3 molecules per nm2. Obtained samples were characterized concerning coating thermal stability by thermogravimetric analysis, nanoparticles surface chemistry by 29Si nuclear magnetic resonance, textural characteristics by low-temperature N2 adsorption-desorption analysis, and dispersibility in oleophilic phases by laser scattering analysis. © 2009 American Chemical Society.