Laser-induced emission of TiO2 nanoparticles in flame spray synthesis

Oxide nanoparticles are widely studied because of their unique properties, including their crystalline phase, surface area, and porosity, which make them attractive for several applications. These properties are related to the increase in the surface/volume ratio when moving from the bulk to the nanoscale. For this reason, a diagnostic tool capable of monitoring the nanoparticle size and concentration during synthesis is particularly valuable. The laser-induced incandescence technique is widely used to provide such information. This study explored the applicability of this technique to TiO2 nanoparticles in flame spray synthesis. The fluorescence, flame emission, and incandescence signals were investigated. Time-resolved spectral measurements were first carried out on TiO2 nanoparticles deposited on a filter. At low laser fluences, the fluorescence signal of anatase TiO2 nanoparticles was detected. At higher fluences, the incandescence signal appeared. A fluence threshold limit that depended on the matrix effect was observed, above which breakdown phenomena occur. Then, laser-induced incandescence spectral measurements were performed on the flame spray at different heights above the burner and different acquisition delay times. The analysis showed the applicability and challenges in using this diagnostic tool in flame spray synthesis.