(466c) One Step, Gas-Phase Synthesis of Hydrophobic TiO2 Nanoparticles

The development of nanomaterials has led to the need for rapid and scalable nanoparticle surface modification for a wide range of applications. In particular, hydrophobic, organic coatings on the surface of inorganic nanoparticles make them compatible to many organic environments, e.g. in sunscreens, (polymer) nanocomposites and biomedical applications. Here, hydrophobic TiO₂ particles were made in one step in a flame reactor by silylation of the surface hydroxyl groups. Titania nanoparticles were produced by flame spray pyrolysis (FSP) and the freshly-formed aerosol was mixed with a fine spray of octyltriethoxysilane (OTES) in water/ethanol solution.^[1,2] The TiO₂ aerosol was rapidly cooled by gas quenching to achieve a temperature of 270 to 370 °C at the coating spray inlet. The particles were characterized by transmission electron microscopy (TEM), X-ray diffraction and nitrogen adsorption. The coating quantity and its chemical structure were assessed by thermogravimetric analysis (TGA) coupled with mass spectroscopy (MS), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) and Raman spectroscopy. The influence of titania specific surface area (SSA) and OTES concentration on the coating quantity was investigated. The TiO₂ surface was covered with carbon chains at an average density of 2 OTES/nm² and these surface groups were thermally stable up to 300 °C. At higher temperatures a weight loss of 2.9 wt% was recorded by TGA for TiO₂ particles with a specific surface area of 38 m²/g. Suspensions of the hydrophobic particles in 2-ethylhexanoic acid and xylene were stable over several weeks, whereas uncoated, hydrophilic TiO₂ sedimented.

[1] Height, M.J., A. Teleki, M. File, and S.E. Pratsinis, ?Surface functionalization and coating of flame-generated nanoparticles,? WO 2006/116887 A1 (2006).

[2] Teleki, A., M. C. Heine, F. Krumeich, M. K. Akhtar, and S. E. Pratsinis, In situ coating of flame-made TiO₂ particles with nanothin SiO₂ films, Langmuir 24, 12553 (2008).