Master of Science in Biological and Agricultural Engineering (MSBAE)
Biological and Agricultural Engineering
Synthesis of micro/nanomaterials within confined flow-based systems such as microfluidics has always been a promising research. However, the inability to scale up reagent volumes due to geometric constraints and pressure development within the channels at higher flow rates has limited their usage. In recent times, millifluidics has emerged as a useful technique where, apart from the synthesis, the in situ characterization of materials becomes easier. In this study, formation of morphology-controlled gold structures at different time intervals (viz. 1, 5, and 9 h) within a millifluidic chip reactor was investigated using gold chloride and dimercaptosuccinic acid (DMSA) as precursor reagents and sodium borohydride as the reducing agent. The structures formed were characterized using 3-D X-ray tomography, X-ray absorption near edge spectroscopy (XANES) and scanning electron microscopy (SEM). The X-ray tomography results show that the dimension of the gold structures vary with respect to their time of deposition within the channel. The gold structures formed at 1 h are 26 µm wide, 5 h are 55 µm wide and 9 h are 100 µm wide. However, the height of the gold structures remained relatively uniform and peaked at 27.5 µm for all the samples. The XANES results show that there are differences in the chemical nature and bonding of the structures before and after reduction with sodium borohydride. A linear combination fitting of the XANES spectra show 50% Au and 50% S with both Au-Au and Au-S bonding for the structures before reduction and 83% Au, 17% S predominantly Au-Au bonding after reduction with borohydride. The SEM of the gold structures show hemispherical shape for sample formed for 9 h, flower-shape for 5 h and polygonal-shape for the 1 h sample. The catalytic activity of these gold structures was also demonstrated through 4-nitrophenol and Ferricyanide conversion reactions. In both the conversion reactions, the gold structures formed for 9 h flow time show better catalytic performance in terms of yield with 90.5% conversion for 4-nitrophenol and 85.5% conversion for Ferricyanide.
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Navin, Chelliah V., "Morphology controlled coating of catalytically active gold structures within flow-focused millifluidic reactor" (2012). LSU Master's Theses. 4200.
Theegala, Chandra S.