Understanding Changes to the Surface of Silver Nanocubes during Their Polyol Synthesis, Processing, and Seeded Growth
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Huang, Qijia
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Abstract
Silver nanocubes have been extensively studied owing to their remarkable plasmonic and catalytic properties. Despite the success in synthesis, a detailed understanding of the surface chemistry during and after the synthesis remains elusive. This dissertation leverages the high sensitivity of surface-enhanced Raman scattering (SERS) to probe the native surface of Ag nanocubes. In the first part of my thesis, I investigated Ag nanocubes synthesized using an HCl-mediated polyol method. I provided direct evidence to support the presence of Cl- on the surface of Ag nanocubes while they were suspended in the original reaction solution by resolving the Ag–Cl vibrational peak. I also investigated the synthesis in the absence of Cl-, proving the crucial role of Cl- in directing shape evolution. Moreover, I demonstrated that solvents used during sample preparation critically influenced surface chemistry and morphology retention. Acetone facilitated reversible aggregation and co-adsorption of carbonyl groups and Cl-, which suppressed oxidative etching and improved recovery during collection. Subsequent washing with water or ethanol enables effective redispersion while facilitating the desorption of Cl- ions and the adsorption of poly(vinyl pyrrolidone) (PVP). The second part of my thesis investigated surface changes during seed-mediated growth of Ag nanocubes in an aqueous system. SERS revealed ligand exchange between PVP and the Cl- from CTAC, and the deposition of AgCl on Ag seeds. Upon addition of ascorbic acid, electron transfer increased surface electron density, enhancing SERS signals and enabling direct reduction of AgCl into Ag. Collectively, my thesis contributes to a deeper understanding of the mechanisms governing the synthesis and preservation of Ag nanocubes, offering guidance for the rational synthesis of Ag nanocrystals.
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2025-07-30
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Dissertation