Page 124 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Chapter 6
array reactor will remain very compact and is estimated to occupy only a small spatial footprint, which is favorable for eventual industrial-scale application.
6.4 Analysis of Synthesis Mechanism
In general, the plasma-liquid interaction is a complex physicochemical process that involves reactions among electrons, ions, neutral radicals and molecules. Therefore, an analysis of kinetics of Y(OH)3 formation and precipitation in the reactor is rather difficult, for they are affected by several factors, such as the electron penetration, precursor concentration, diffusion speeds of ions, pH and the solution temperature. In the studied process, since the SS electrode is biased negatively with respect to the liquid electrode, plasma electrons are supposed to be driven toward the solution surface and react with water molecules, giving rise to H and OH radicals.
To confirm the dissociation of water molecules and identify the intermediate radicals, in situ optical emission measurements were carried out in our study. Figure 6.10 shows a representative review spectrum recorded during the plasma treatment of yttrium nitrate solution, and detailed radiative transition information is summarized in Table 6.2. The most prominent peaks in the wavelength region of 690-850 nm correspond to Ar I (4p→4s) lines.32 In addition, less intense emission signals are also observed in the region of 305-310 nm, 657 nm and 777 nm, which were assigned to the OH bands, atomic hydrogen (Hα) and atomic oxygen.33,34 The presence of these signals proves that water molecules are decomposed under the plasma-liquid interactions.
Table 6.2 Summary of emission lines collected from spectra32–36
Species OH H
O Ar
System 3064 Å system Balmer series
Ar I
Transition A 2Σ+→X 2∏
n→2s,2p 3p5P→3s5S 4p→4s
Wavelength 306.6 nm, 308.9 nm
657.2 nm (Hα)
777.2 nm
696.5 nm, 706.7 nm, 738.4 nm, 750.4 nm, 763.5 nm, 772.4 nm, 794.8 nm, 826.5 nm, 842.5 nm
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