• López-Cámara, Claudia-Francisca
• Fortugno, Paolo
• Dasgupta, Malini
• Wiggers, Hartmut

Abstract

<p>Inline particle coating after the particle formation process to preserve its specific properties is hardly investigated scientifically. Tackling that issue, we have studied the use of three different vaporized organo-siloxanes (tetraethyl orthosilicate TEOS, hexamethyldisiloxane HMDSO, and octamethylcyclotetrasiloxane OMCTS) as precursors for direct inline coating of pristine titanium dioxide (TiO₂) nanoparticles made via spray-flame synthesis. The inline silica (SiO₂) coating of the formed titanium dioxide nanoparticles is achieved by vaporizing and sending the chosen organo-siloxane precursors into a cylindrical coating nozzle downstream the particle formation zone of the spray-flame. To further explore the effects on morphology and the quality of the resultant TiO₂|SiO₂ core-shell nanoparticles, a plasma discharge – i.e., dielectric barrier discharge source – is applied after the coating step. The TiO₂|SiO₂ core-shell nanoparticles are characterized using Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy (STEM), X-Ray Diffraction (XRD), Fourier-Transform InfraRed spectroscopy (FTIR), Brunauer-Emmett-Teller surface area analysis (BET), elemental analysis, and dynamic light scattering (DLS). Results showed distinct core-shell nanoparticles with shell thicknesses of around 1.5 nm alongside the formation of unattached SiO₂ nanoparticles due to homogenous nucleation of SiO₂. As the precursor silicon content increased (TEOS &lt; HMDSO &lt; OMCTS), the homogenous nucleation rose to generate materials with high BET surface areas. When employing OMCTS, the high homogeneous nucleation rate led to SiO₂ agglomeration, which resulted in large TiO₂|SiO₂ agglomerates. Morphologically, the phase composition of anatase/rutile of the produced coated nanoparticles did not vary significantly when compared with the reference uncoated TiO₂ nanoparticles, indicating that the SiO₂ coating is purely a surface phenomenon. Plasma discharge was shown to reduce coated particle agglomeration up to certain extend. Based on these findings, we conclude that the best studied parameters to benefit the synthesis of homogeneously coated TiO₂|SiO₂ nanoparticles are (i) using TEOS as a coating precursor to minimize SiO₂ homogeneous nucleation and (ii) applying a plasma discharge to slightly reduce coated particle agglomeration.</p>

Topics

• nanoparticle
• impedance spectroscopy
• surface
• phase
• x-ray diffraction
• transmission electron microscopy
• Silicon
• titanium
• dynamic light scattering
• infrared spectroscopy
• elemental analysis