Page 125 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Yttrium Oxide Nanoparticles Synthesis - a Model Study on the Plasma-Liquid Interaction and Opener to Nanophosphors
1200
1000
800
600
400
OH
200 0
Ha 656.3 nm
648 650 652 654 656 658 660 662 664 666
Wavelength (nm) O 777.4 nm
300
400 500 600 700 800 900
Wavelength (nm)
(a) 120 100 80 60 40 20 0
(b) 35 30 25 20 15 10 5 0
-5 a 774 776 778 780 782 784 786 788 790 792
Wavelength (nm)
Ar lines
O
Intensity (a.u.)
Intensity (a.u.) Intensity (a.u.)
Figure 6.10 Optical emission spectrum collected during the plasma-liquid interactions
The excited OH radicals are not stable and can easily combine with electrons to form OH- ions in the liquid phase. When their concentration increases to a certain value, Y3+ cations will be hydrolyzed to form colloidal yttrium hydroxide particles and deposit from the solution. Briefly, the deposition of yttrium hydroxide in the micro reactor can be explained by the following two-step electrochemical-chemical mechanism:
Next, we analyzed the relationship between Y(OH)3 solubility and the dynamically evolving pH value of the solution to get a better understanding of the synthesis process. Theoretically, the solubility constant Ks of Y(OH)3 and the solution temperature follows the classic Van't Hoff equation:
dInKs = DHq (6.1) dT RT2
where ∆Hθ is the standard dissolution enthalpy of Y(OH)3, R is the ideal gas constant, and T is the solution temperature. Since the dissolution enthalpy of Y(OH)3 is negligible 37, the Ks of Y(OH)3 for the solution during plasma treatment can be assumed as an approximation to the Ks of Y(OH)3 at room temperature (10-22.1).21 Therefore, combined with the ionization constant of water (10-14), the pH value that will start precipitation (pHst) of Y(OH)3 can be derived from the following formulas:
113
H