Page 54 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Chapter 3
3.1 Introduction
To assess the benefits and challenges of the microplasma-assisted nanomaterial synthesis on the model case of the novel technological platform, and to investigate plasma parameters as well as underlying mechanisms of precursor dissociation process, we firstly studied synthesis of nanomaterials in the gas phase from metallocene precursors.
Iron oxides are widespread in nature and have served humans for centuries. They exist in many forms, with maghemite (γ-Fe2O3), hematite (α-Fe2O3) and magnetite (Fe3O4) being the most common states. Due to their magnetic behavior and properties such as chemical stability, biocompatibility, and environmental safety, nano-sized iron oxide have been exploited not only for fundamental scientific interest but also for a broad range of applications, such as magnetic recording media, targeted drug delivery, catalysts, magnetic resonance imaging and ferrofluids.1–3 Emerging applications of the nanostructured iron oxide are also in CO2-neutral energetics induced by unique photoelectrochemical properties.4 Although significant progress has been achieved in synthesis of iron oxide nanostructure and their applications, it’s still a challenge to produce high quality iron oxide nanoparticles of adjustable size in a continuous and tunable process.
Present study employs ferrocene as a precursor reagent, which is an organometallic compound consisting of two cyclopentadienyl rings (C5H5-) sandwiching an iron ion (Fe2+). Due to the stability at room temperature, relatively high vapor pressure, low flammability and toxicity, ferrocene is widely chosen as the precursor for the gas phase synthesis of Fe nanoparticles by different methods, including thermal decomposition,5,6 laser-assisted photolysis,7–9 atomic layer deposition (ALD)10,11 and plasma-enhanced chemical vapor deposition (PECVD).12,13 However, detailed mechanism of ferrocene decomposition is still not clear. It is because ferrocene pyrolysis is a complex process consisting of a series of consecutive, parallel as well as catalytic reactions in homogeneous or heterogeneous phase.14 The situation becomes even more complicated in plasma phase due to the multiple reactions involving electrons.
The goal of present study was to design a continuous, simple and environmentally friendly process for controllable synthesis of high quality nanoparticles, to provide detailed characterization of the products for differet operating conditions and to get an insight into the ferrocene decomposition process in plasma. This was carried out via the gas phase synthesis of small and uniform iron oxide nanoparticles by dissociating ferrocene vapors in argon mirodischarges. Moreover, combining experimental and literature data, a simplified zero- dimensional modeling based on Bolsig+ solver for electron energy distribution function (EEDF) was carried out to estimate characteristic value of electron temperature in the microplasma column. Despite simplicity, this estimation can give valuable insight into relative contribution of the processes characterized by the different energy thresholds in plasma-chemical dissociating mechanisms.
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