Sub-nanoscale Surface Engineering of TiO₂ Nanoparticles by Molecular Layer Deposition of Poly(ethylene terephthalate) for Suppressing Photoactivity and Enhancing Dispersibility

Abstract

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. TiO 2 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 TiO 2 NPs by hindering the access of water and reactant molecules to the TiO 2 surface but also improve the dispersibility of TiO 2 NPs in both organic and aqueous media. Still, the bulk optical properties, electronic structure, and surface area of TiO 2 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 TiO 2 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 subnanometer scale, particle MLD can serve many other applications ranging from nanofluids to emulsions to polymer nanocomposites.

Atomic/Molecular Layer Deposition for Designer's Functional Metal–Organic Materials

“…New organic components have also been developed for the purely organic MLD processes; the MLD material library already includes, besides the initially introduced polyimides [ 15,17–22,137–143 ] and polyamides, [ 15,23–28,144–149 ] many other polymers: polyurea, [ 29,30,37,38,51,150–164 ] polythiourea, [ 52 ] polyurethane, [ 165,166 ] polyazomethine, [ 167–172 ] poly(3,4‐ethylenedioxy‐thiophene), [ 173–177 ] polyimide–polyamide, [ 141 ] poly(ethylene terephthalate) (PET), [ 50,178–180 ] and others. [ 31,32,39–44,176,181–200 ] In recent years, the organic precursor library has been rapidly expanding.…”

Molecular Layer Deposition of Polyurea on Silica Nanoparticles and Its Application in Dielectric Nanocomposites

“…In this regard, gas-phase methods offer remarkable advantages . Molecular layer deposition (MLD) is a robust technique to deposit organic films on flat surfaces as well as NPs from gaseous precursors. − As opposed to the conventional chemical vapor deposition (CVD), MLD utilizes self-limiting reactions between bi-functional precursors to grow organic films on the solid surface in a controlled layer-by-layer fashion by dosing sequential pulses of each precursor into the reactor . The controllability of MLD enables conformal reproducible depositions on the NPs, which is of great importance in nanocomposite applications where the interface between the NP and the host polymer matrix determines the performance of the material .…”

Tailoring the Flow Properties of Inhaled Micronized Drug Powders by Atomic and Molecular Layer Deposition

“…Different from the conventional dry coating methods, atomic layer deposition (ALD) is a vapor deposition technique where an ultrathin film grows by sequential exposure of gas-phase reactants onto the target material with atomic layer accuracy [7][8][9]. Due to the advantages of excellent conformality and film thickness control at the atomic level, ALD offers the possibility of coating primary particles as well as complex structures with a large surface area to functionalize the surface properties of targeted materials for improving different product performances [10][11][12][13][14][15][16], such as modifications of wetting [17], acid-base [18], optical, mechanical and rheological properties [19][20][21]. Although ALD is popular among the scientific community for modifying the surface properties of materials, this technique has been mainly used on flat substrates or fibers [22][23][24].…”