Subnano Surface Engineering of TiO2 Nanoparticles by PET Molecular Layer Deposition: Tuning Photoactivity and Dispersibility

In this work, we report molecular layer deposition (MLD) of ultrathin poly(ethylene terephthalate) (PET) films on gram-scale batches of ultrafine particles for the first time. TiO₂ P25 nanoparticles (NPs) are coated up to 50 cycles in an atmospheric-pressure fluidized bed reactor at 150 °C using terephthaloyl chloride and ethylene glycol as precursors. Ex-situ diffuse reflectance infrared Fourier transform spectroscopy, thermogravimetric analysis and transmission electron microscopy show the linear growth at 0.05 nm/cycle of uniform and conformal PET films, which are unattainable with conventional wet-phase approaches. The subnano and nano PET films not only suppress the photocatalytic activity of TiO₂ NPs by reducing the generation of hydroxyl radicals, but also improve the dispersibility of TiO₂ NPs in both organic and aqueous media. Still, the bulk optical properties, electronic structure and surface area of TiO₂ are essentially unaffected by the MLD process. This study demonstrates the industrial relevance of MLD to simultaneously tune the photoactivity and dispersibility of the commercial photocatalyst TiO₂ P25. Moreover, by rapidly modifying the surface properties of particles in a controlled manner at the subnanometer scale, particle MLD can serve many applications ranging from nanofluids to emulsions to polymer nanocomposites.