Using surfactant-based colloidal systems to promote photoinduced synthesis of silver nanoparticles
This thesis focuses on the photo-initiated synthesis of silver nanoparticles in water with low concentration of stabilizing agents to investigate the role that surfactants, specifically their charge, plays in the synthesis. The employed stabilizing agents include sodium dodecyl sulfonate (SDS), sodium-dodecyl-benzenesulfonate (SDBS), and cetyltrimethylammonium tosylate (CTAT) surfactants along with SDBS-rich and CTAT-rich surfactant vesicles. The formation of silver nanoparticles is monitored by the color change of the reaction mixture from clear to yellow that arises from the onset of a strong, visible absorption band that is due to the surface plasmon resonance (SPR) that is characteristic of AgNPs. By comparing the product generated from different stabilizers, we found that above the critical micelle concentration (CMC), both negatively charged surfactants, SDS and SDBS, work well for promoting the formation of AgNPs whereas the positive charged surfactant, CTAT, is not suitable for the synthesis. With SDS and SDBS, the anionic interface recruits silver cations in a counter-ion cloud around the micelle and also provides a passivating layer to limit the growth of the nanoparticle. The use of vesicle-forming, mixed-surfactant preparations was also investigated using both SDBS-rich and CTAT-rich mixtures. It was found that while SDBS-rich vesicles are optimal for preparing AgNPs with a distinct SPR band and good yield, CTAT-rich vesicles result in AgNPs with a broad SPR band characteristic of a polydisperse preparation. The SDBS-rich vesicles are therefore deemed the best formulation for yielding AgNPs since it has high yield with minimal added surfactant due to the micromolar critical aggregation concentration (CAC), and the ability to recruit more silver cations at the bilayer interface. This result is valuable since the use of less surfactant could be advantageous from a cost perspective and if the goal is to produce samples with minimal surfactant in the product.