Page 127 - 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
6.5 Conclusions
We have demonstrated, for the first time, the successful synthesis of Y2O3 nanoparticles via a simple, microplasma-assisted solution treatment followed by calcination step. The excited radicals during plasma-electrodeposition were in situ monitored by optical emission spectroscopy. The products were examined by complementary analytical methods such as TG/DSC, SEM, EDX, FT-IR, Raman, TEM, SAED, XRD and XPS to characterize their composition, morphology and structure. Experimental results show that high purity, crystalline Y2O3 nanoparticles of adjustable size are produced by the studied process. At relatively low annealing temperature of 600 °C particles are smaller and more uniform, with a size distribution of 8-15 nm. The increase in annealing temperature contributes to larger sized nanoparticles with broader size distribution, in the range of 30~80 nm at 1200 °C. A microplasma-array design is proposed for potential scaling up of the process towards industrially viable production. Finally, the mechanistic aspects of the synthesis process are discussed, based on in situ emission spectroscopy measurements, experimental results and an analysis of the precipitation equilibria.
Compared to traditional wet chemistry methods for the synthesis of Y2O3 nanoparticles, this novel process is free of toxic chemicals solvents or stabilizers such as oxalic acid, NaOH, citric acid and poly(oxyethylene)5 nonyl phenol ether. Instead, the studied approach allows the fabrication of Y2O3 nanoparticles from merely aqueous solutions of yttrium nitrates, which also avoids possible byproducts or impurities and the associated complex purification procedures. In terms of operation, conventional methods are mostly based on forced hydrolysis of yttrium salt solutions, requiring precise control of operational parameters to achieve a mild and uniform hydrolysis condition. By contrast, in the studied process the generation and release of OH- takes place in an inert atmosphere and can be directly adjusted by tuning plasma powers, ensuring a facile condition. These advantages in combination with the feasibility to scale up the process via the microplasma array design will make the technique attractive for industrialization. Moreover, this study has extended the microplasma- assisted approach to the synthesis of Y2O3 nanoparticles, which is also expected to open up the route for the fabrication of rare earth oxides series, such as Eu2O3, Yb2O3, Gd2O3, CeO2, La2O3, etc., just by changing corresponding precursors. In addition, the environmentally friendly plasma-electrodeposition system may also benefit biomedical nanoparticles synthesis in terms of the toxic-chemical free process and mild reaction condition.
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