New Perspectives in Monitoring the Flame Synthesis of Iron Oxide Nanoparticles: Addressing Solid and Gas-Phase Diagnosti
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New Perspectives in Monitoring the Flame Synthesis of Iron Oxide Nanoparticles: Addressing Solid and Gas-Phase Diagnostics Challenges Igor Rahinov1*, Marina Poliak2, Alexey Fomin2, Vladimir Tsionsky2 and Sergey Cheskis2 1 Department of Natural Sciences, The Open University of Israel, Raanana 4353701, Israel. 2 School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel. ABSTRACT Several techniques for in-situ monitoring and characterization of flame synthesized nanoparticles are described with the goal of gaining further insight into the mechanisms governing nanoparticle (NP) formation in flame reactors. These include: a combined particle mass spectrometer - quartz crystal microbalance apparatus (PMS-QCM); The Light Induced Detuning –Quartz Crystal Microbalance (LID-QCM) method; Application of Intra Cavity Laser Absorption Spectroscopy (ICLAS) for monitoring gas phase intermediates in a particle laden environment. INTRODUCTION Flame-assisted synthesis offers a convenient route for scalable production of nano-shaped smart materials with controlled functionalities. The combination of combustion and aerosol science paved the way to synthesis of high purity materials with novel metastable phases, inaccessible by traditional wet-chemistry methods. The flame-assisted synthesis methodology enables to produce a plethora of functional materials, such as: mixed metal oxides, metal salts and supported noble metals [1,2]. Among other flame-synthesized materials, iron oxide nanoparticles are used in diverse applications, including optical magnetic recording, catalysis, gas sensors, targeted drug delivery, magnetic resonance imaging, and hyperthermic malignant cell therapy (see for instance review by Lu et al. [3] and references therein). The NP properties are dependent on their characteristics, such as, size distribution, phase and morphology. These characteristics depend in turn on flame conditions (e.g., fuel/oxidizer ratio, temperature), choice of a flame fuel, particle precursor, and the position where the particles are collected. Detailed understanding of the mechanism governing the particle formation in flames is a necessary prerequisite for flame synthesis of NPs with tailored functionalities. A comprehensive mechanism validation requires quantitative diagnostics of both gas-phase molecular precursors (e.g. FeO) and nascent solid iron oxide NPs. While there is an ample evidence of metal clusters formation in flames fed with noble metal precursors [see ref. 1 and references therein], the evidences of metal clusters formation are scarce for flames doped with iron-containing precursors. The "traditional" mechanisms of iron oxide NP formation postulate precursor decomposition leading to formation of Fe-atoms, the gas phase oxidation of which followed by nucleation generate iron oxide NPs at large distances from the surface of the burner. Here we describe experiments capable of delivering quantitative information regarding gas-phase intermediates and solid phase particulates as means to gather further insight into the mecha
