Page 116 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Chapter 6
6.2.2 Characterization
Thermogravimetric analysis was performed using a Mettler Toledo TGA/DSC 1 instrument. Approximately 10 mg of sample was placed in an alumina crucible and heated to 750°C at a rate of 10°C/min in a flow (60 ml/min) of 33/67 (v/v) mixture of O2/He. SEM characterization was performed on a Quanta 3D FEG (FEI) operated at 10 kV, with a silicon drift EDX detector (Sapphire DPP-2) to examine chemical composition. FT-IR measurements were carried out by employing Perkin-Elmer Spectrum One Fourier transform IR spectrometer. Raman measurements were performed by using a Labram confocal Raman microscope (Horiba Jobin-Yvon) equipped with a laser diode emitting at 632 nm. TEM analysis was carried out by a FEI Tecnai 20 (Sphera) microscopy, operating with a 200 kV LaB6 filament. The crystal structure was determined by X-ray diffraction (XRD) with a Rigaku Powder Diffractometer using Cu-Kα1 radiation (λ=1.54056 Å). The scans were recorded in 2q steps of 0.02 degrees and a dwell time of 25s. The chemical compositions and binding information were furtherly assessed by an X-ray photoelectron spectroscopy (Thermo Scientific Kα), with spectrum being recorded by an aluminium anode (Al Kα=1486.6 eV). In order to investigate the plasma-liquid interaction, electrical measurements were carried out by recording experimental values of the plasma current, voltage and power using a LabVIEW based program. The optical emission spectrum (OES) of the operating discharge was also in situ recorded by an HR4000 spectrometer (Ocean Optics, Inc.), with emitted light being collected by an optical fiber fixed at 20 mm from the electrodes axis.
6.3 Results and Discussions
To give a general overview of the plasma current, voltage and power evolution during a specific plasma-liquid interaction process, a typical V-I characteristic of the microdischarge is shown in Supplementary Material Figure S1. The plasma current decreases slightly in time, while the plasma voltage and power show an apparent rising trend. This is attributed to the consumption and depletion of the electrolyte solution resulting in higher resistivity as well as to water evaporation during the experiment, which leads to an increased distance between the cathode and the liquid surface. Moreover, it is revealed that the plasma-liquid interactions can be sustained at extremely low power consumption (3-6 W), which is also a distinctive advantage of the presented technique.
Time-evolution images of yttrium nitrate solution under plasma treatment are presented in Supplementary Material Figure S2. The bulk electrolyte solution remains colorless in the first 30 min. As the plasma operates for 1 hour, the transparent solution gradually turns into lightly white, becoming semitransparent approximately after 90 min of plasma exposure. As the plasma treatment of the electrolyte continues, the white solution becomes increasingly turbid, and turns an opaque creamy white after approximately 150 min. During this process one can clearly observe that white floccules deposit in the electrolyte, indicating the generation of yttrium hydroxide compounds.
Thermal analysis (TG and DSC) was carried out to investigate the thermal behavior and decomposition process of the obtained yttrium hydroxide compounds (Figure 6.2). A wide endothermic peak is observed in the range of 50-150 °C, relating to the dehydration of free 104