Sub-nanoscale Surface Engineering of TiO2 Nanoparticles by Molecular Layer Deposition of Poly(ethylene terephthalate) for Suppressing Photoactivity and Enhancing Dispersibility
2020
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 sub-nanoscale and nanoscale PET films not
only suppress the photocatalytic activity of TiO2 NPs by
hindering the access of water and reactant molecules to the TiO2 surface 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 suppress the photoactivity and
enhance the dispersibility of commercial TiO2 P25 nanopowders,
which is crucial for their use for example as UV-screening agents
in sunscreens and as white pigments in paints. Moreover, by rapidly
modifying the surface properties of particles in a controlled manner
at the sub-nanometer scale, particle MLD can serve many other applications
ranging from nanofluids to emulsions to polymer nanocomposites.
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