Synthesis of Titanium Dioxide Nanoparticles Using a Double-Slit Curved Wall-Jet Burner

ABSTRACT

A novel double-slit curved wall-jet (DS-CWJ) burner was proposed and utilized for flame synthesis. This burner was comprised of double curved wall-jet nozzles with coaxial slits; the inner slit was for the delivery of titanium tetraisopropoxide (TTIP) precursor while the outer one was to supply premixed fuel/air mixture of ethylene (C₂H₄) or propane (C₃H₈). This configuration enabled rapid mixing between the precursor and reactants along the curved surface and inside the recirculation zone of the burner. Particle growth of titanium dioxide (TiO₂) nanoparticles and their phases was investigated with varying equivalence ratio and Reynolds number. Flow field and flame structure were measured using particle image velocimetry (PIV) and OH planar laser-induced fluorescence (PLIF) techniques, respectively. The nanoparticles were characterized using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and nitrogen adsorption Brunauer–Emmett–Teller (BET) for surface area analysis. The flow field consisted of a wall-jet region leading to a recirculation zone, an interaction jet region, followed by a merged-jet region. The DS-CWJ burner revealed appreciable mixing characteristics between the precursor and combustion gases near the nozzle regions, with a slight increase in the axial velocity due to the precursor injection. The precursor supply had a negligible effect on the flame structure. The burner produced a reasonably uniform size (13–18 nm) nanoparticles with a high BET surface area (>100 m²/g). The phase of TiO₂ nanoparticles was mainly dependent on the equivalence ratio and fuel type, which impact flame height, heat release rate, and high temperature residence time of the precursor vapor. For ethylene flames, the anatase content increased with the equivalence ratio, whereas it decreased in the case of propane flames. The synthesized TiO₂ nanoparticles exhibited high crystallinity and the anatase phase was dominant at high equivalence ratios (ϕ > 1.6) for C₂H₄, and at low equivalence ratios (ϕ < 1.3) for the C₃H₈ flame.

KEYWORDS:

• Double-slit curved wall-jet (CWJ) burner
• Flame synthesis
• OH-planar laser-induced fluorescence (OH-PLIF)
• Particle image velocimetry (PIV)
• Titanium dioxide nanoparticles

Acknowledgment

The authors are indebted to Dr. Hua Tan at the Analytical Core Lab at KAUST for BET measurements.

Additional information

Funding

The authors are grateful for the research fund from the Clean Combustion Research Center (CCRC) at King Abdullah University of Science and Technology.