Synthesis of Silver Iodide Nanoparticles Using a High-Gravity System

• Main Authors: Chih-Chan Li, 李誌展
• Other Authors: 戴怡德
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/01437009678542627270

碩士 === 國立臺灣大學 === 化學工程學研究所 === 98 === The AgI nanoparticles have unique optical, electrical and catalytic properties that make it useful in industrial applications. The common methods for preparing AgI nanoparticles include reverse microemulsion and reactive precipitation. The size of particle synthesized by reverse microemulsion is tunable by controlling the ratio of the water, oil and surfactant. However, this method is difficult to scale up due to low production rate and high cost. It is also difficult to obtain uniform particles through the reactive precipitation method using a stirred tank reactor because of the poor mixing efficiency. To improve mixing efficiency, a high-gravity (Higee) reactive precipitation method has been introduced, which is the technique using centrifugation force to enhance the mass transfer rate and micromixing. In this research we used the Higee technique to prepared AgI. After trying various protecting agents, we chose PVP, PEG and BPEG as protecting agent to proceed a systematic study. The effects of operation variables, including reactant concentration, protecting agent concentration, and rotation speed were investigated. Finally we used particle size analyzer and an electron microscope to analyze the size of prepared AgI. Our results showed that when the reactant concentration is 0.20 M using 10.00 g/L PVP as protecting agent, the number mean particle size of re-dispersed slurry was 47.6 nm and the volume mean size was 66.3 nm, but the SEM image showed that agglomerates formed after drying. When the reactant concentration is 0.20 M using 5.00 g/L PEG as protecting agent, the number mean particle size of re-dispersed slurry was about 134.8 nm, and the volume particle size distribution had two peaks due to agglomeration. When using BPEG as protecting agent the particle size was small than the one using PEG, but high rotation speed result in foaming, which would influence the consequent separation and purification steps. As to the rotation speed effect is concerned, no matter the rotation was 500, 2000 or 4000 rpm, we obtained similar volume particle size distribution(PSD) and number particle size distribution when the reactant concentration was 0.20 M using 10.00 g/L PVP as protecting agent. When the reactant concentration was 0.20 M using 5.00 g/L PEG or 5.00 g/L BPEG as protecting agent, the rotation speed had a remarkable influence on the volume PSD. As the rotation speed was increasing, the percentage of agglomerated particles was decreasing. This showed that higher rotation speed enhanced the mixing efficiency. It is well known that β/γ-AgI undergoes a phase transition into α-phase when the temperature is above 147℃ at normal pressure. In our research, when using DSC to study the first order phase transition temperature of the prepared AgI, we found that the phase transition temperature Tβ/γ→α shifts to higher temperature and Tα→β/γ shifts to lower temperature when using PVP as protecting agent. The two temperatures form a large hysteresis loop which was related with particle size and protecting agent. It is well known that α-AgI is a typical superionic conductor with conductivity up to 1 Ω-1cm-1. If we can stabilize α-AgI at room temperature, we can broaden its applications to many electronic products such as solar cell and sensor.