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.