Synthesis of Plasmonic Metal-Based Hybrid Nanostructures and Their Catalytic Applications

Abstract

Noble-metal nanoparticles have created intensive research efforts in catalysis, electronics, sensors, and bioimaging. The majority of these applications rely on the confined surface plasmon resonance, which is peculiar to noble-metal nanostructures. At a given resonance wavelength of the input light, this localized surface plasmon resonance is coupled with charge density oscillation within the particles and causes strong electromagnetic field confinement around the nanoparticle. The properties of LSPR are highly sensitive and depend on the material shape, size, dielectric environment, and the local refractive index around nanoparticles. Thus, the nanoparticles for enhancement of these properties have been elaborated. Compared with the monometallic nanostructures, hybrid nanostructures formed by two or more different nanomaterials are adapted to develop bimetallic and metal-semiconductor nanostructures. Hybrid nanostructures with a versatile approach to fabricate the ideal nanocatalysts that meet industrial applications have recently triggered much research interest. However, the fabrication of hybrid nanostructures with both facile, and fascinating morphology remains a challenge. In this thesis, high-performance catalysts are created using aqueous-solution-based hybridization methods based on chemical conversion of noble metal nanostructures' surfaces. A rapid surface sulfidation was conducted to synthesize hybrid metal (bimetallic Cu-Au) and metal – semiconductor nanostructures (Cu@Cu2S and PdAuAg-AuAgS) by using sodium sulfide as the sulfur source. Characterization methods such as X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), and energy dispersive X-ray spectroscopy (EDS), were employed to confirm that the as-synthesized nanoparticles were heterogeneous hybrid nanostructures. The as-synthesized hybrid nanostructures (Cu-Au) and hybrid metal – chalcogenides semiconductor nanoparticles (Cu@Cu2S and PdAuAg-AuAgS) were suggested as an efficient catalyst for the 4-nitrophenol (4-NP) hydrogenation, and methylene blue (MB) decomposition, respectively. The reductive degradation of these pollutants in the presence of metal-semiconductor nanoparticles gave better performance compared to monometallic nanostructures. In order to achieve nanostructures with the incorporation of semiconductors, a comparison of the catalytic activity of both nanocatalysts was done. The catalytic performance of the nanocatalyst with semiconductors was found to be the best. This result confirmed the synergistic effects of charge migration and effective charge separation between those components.