Nanomaterials from the gas phase: mechanism of iron oxide particle formation during flame assisted synthesis

Igor Rahinov, Department of Natural Sciences, Chemistry Division, The Open University of Israel, Raanana, ISRAEL

Combustion is an important synthetic tool for scalable production of nanosized metal oxide materials with tailored functionalities. Iron oxide nanoparticles can be coveniently produced via combustion synthesis. They have a plethora of applications ranging from targeted drug delivery to heterogeneous catalysis and gas sensing. A crucial prerequisit for intelligent nanoparticle synthesis from the gas phase is the detailed understanding of their formation mechanism.

In this work we have studied the mechanism of iron oxide nanoparticle formation in a methane/air flame doped with iron pentacarbonyl. We have applied the recently developed combined particle mass spectrometry-quartz crystal microbalance technique. This technique encompasses molecular beam sampling electrostatic sorting of charged particles according to their m/z ratio and detecting the neutral particles by measuring the variation of the oscillation frequency of quartz crystal upon deposition of flame synthesized nanomaterial. The measurements were performed in premixed low pressure flat quazi 1-D flame, enabling direct comparison of the experimental results to the output of kinetic simulation. 

Our results unambiguously indicate that nanoparticle formation occures very early in close prior to the luminescence zone of the flame. The the nanoparticle concentrtation drops sharply past the flame front. At large distances from the burner where the temperature decreases the nanoprticles reappear. We show that this behaviour can be rationalized in the framework of the model including iron cluster formation. These observations challenge the existing mechanisms of iron oxide nanoparticle flame synthesis and provide a trigger for their further development.