Laser-based investigation of the transition from droplets to nanoparticles in flame-assisted spray synthesis of functional nanoparticles

• Published in: Proceedings of the Combustion Institute Vol. 36; no. 1; pp. 1109 - 1117
• Main Authors: Liu, Chenyang, Li, Shuiqing, Zong, Yichen, Yao, Qiang, Tse, Stephen D.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 2017
• Subjects: Flame-assisted spray pyrolysis; Functional TiO2-based nanoparticle; Phase-selective LIBS; Transition from droplets to nanoparticles; Flame-assisted spray pyrolysis; Functional TiO2-based nanoparticle; Phase-selective LIBS; Transition from droplets to nanoparticles
• ISSN: 1540-7489; 1873-2704
• DOI: 10.1016/j.proci.2016.06.166

Mechanisms involved in flame-assisted-spray-pyrolysis (FASP) synthesis of TiO2-based functional nanoparticles are investigated using in situ phase-selective laser-induced breakdown spectroscopy. Specifically, the transition from droplets to nanoparticles is examined, as well as the particle growth process in the post flame region. In contrast to vapor-fed flame synthesis, the existence of the precursor breakdown in sprayed droplets is observed by both Ti atomic signal and Bremsstrahlung emissions. The emission signal intensity variation reveals the transition from droplets to nanoparticles, indicating that the competition between precursor vaporization and nascent particle formation is the rate determining factor. For the ensuing particle growth regime, the prediction of the particle size evolution by a polydispersed population balance model is in good agreement with TEM and laser-diagnostics results, demonstrating that the particle growth is governed by the collision-coagulation mechanism. Besides, the transition from droplets to nanoparticles can be accelerated with sufficient OH radicles provided by combustible solvents. Furthermore, doping of TiO2 with V and Zr will lead to changes in band gap of the nanoparticle observed, i.e., a distinct strengthening by 23% with V doping and a weakening by 22% with Zr doping in the intensity of Ti signal, respectively.