Page 160 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Chapter 9
between magnetic property and the process parameters. This is the first detailed investigation on the magnetic properties of nanoparticles synthesized by micro discharge. It is shown that by the microplasma enabled process the magnetic properties of the obtained products can be “in-flight” tuned to a large extent. At the optimized conditions high quality single phase fcc Ni nanoparticles with the size of 20-27 nm and Ms value as high as 44.4 mAm2/g can be obtained. Moreover, the underlying mechanisms of the new and interesting process of CNTs formation from the same metallocene precursor are discussed.
Besides the gas phase synthesis of nanoparticles, in the third stage of the PhD project, the microplasma technique was expanded to the liquid phase nanofabrication. In Chapter 6, the synthesis of a typical host material of luminescent nanostructures (Y2O3 nanoparticles) was chosen as a model case to investigate the microplasma-liquid interaction process, in which high purity crystalline Y2O3 nanoparticles with adjustable sizes were fabricated via a two- step method: plasma electrodeposition of yttrium hydroxide followed by heat-treatment at various temperatures. In this manner, water was exploited as a “soft” OH- source, without involving extra solvents or hydrolyzing agents. Moreover, possible mechanisms for plasma- assisted yttrium hydroxide precipitation were discussed by correlating optical emission spectroscopic studies, plasma kinetic analysis and the precipitation equilibrium.
In Chapter 7, based on the experimental procedures developed in the above study, other lanthanide elements (Ln=Eu, Tb, Dy, Tm) were added in the electrolytes solution to prepare lanthanide (Ln)-doped nanophosphors. Y2O3:Eu3+ nanophosphors were synthesized to study the influence of the heat-treatment and the dopant concentration on the luminescent properties. Results show the heat-treatment can enhance their luminescent efficiency, while the gradual increase in dopant concentration shows a non-monotonic dependency initial positive but a final quenching effect on luminescence. In addition to the Y2O3:Eu3+ nanophosphors, a series of other Ln3+ (Ln=Eu, Tb, Dy, Tm) doped yttria nanophosphors were prepared to demonstrate the versatility of the process.
In Chapter 8, the direct synthesis of Ag nanoparticles from Tollens’ reagent (Ag(NH3)2OH) via the plasma-liquid interactions was reported. Meanwhile, electrochemical synthesis of Ag nanoparticles from silver nitrite (AgNO3) solution was carried out in the same reactor as reference. It was found that Ag(NH3)2OH based process has considerably faster reaction rate and higher conversion efficiency compared with AgNO3 solution. Furthermore, by applying synthesized Ag nanoparticles against E. coli, antibacterial tests were performed. Result shows that the obtained Ag nanoparticles from Ag(NH3)2OH have relatively higher antibacterial activity compared with Ag NPs obtained from Ag+ as well as commercial samples purchased from Sigma-Aldrich, which may due to their higher surface to volume ratio compared to those produced from AgNO3 solution. This research aims to open the bio- application path for the studied microplasma-assisted nanofabrication technique.
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