Title:
Kinetically-Controlled Synthesis Of Mono-, Bi-, And Multi-Metallic Nanocrystals
Kinetically-Controlled Synthesis Of Mono-, Bi-, And Multi-Metallic Nanocrystals
Author(s)
Wang, Chenxiao
Advisor(s)
Xia, Younan
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Abstract
Crucial in a myriad of applications ranging from catalysis to biomedicine, noble-metal nanocrystals exhibit physicochemical properties strongly governed by their size, morphology, and composition. The strong correlations offer opportunities to optimize their figures of merit, thereby augmenting their overall effectiveness. As research advances from simple mono-metallic nanocrystals to multi-metallic and hybrid nanostructures with diverse architectures and atomic distributions, the escalating complexity presents synthetic chemists with ever-increasing challenges. In this dissertation, I develop two general strategies, namely template-mediated growth and dropwise injection of precursor, aiming to control the structural characteristics of mono-, bi-, and multi-metallic nanocrystals, while exploring their potential applications in catalysis and biomedicine.
First, amorphous Se nanospheres were employed as templates to mediate the nucleation and growth of Au nanoparticles through a galvanic replacement reaction. By leveraging the reducing power of Se and the pH-sensitive reaction kinetics, precise control over the size and number of Au particles on each Se sphere was achieved, resulting in hybrid nanoparticles with diverse morphologies. The presence of Au patches on these hybrid nanoparticles provides an experimental handle to optimize the ligand distribution, significantly augmenting cellular uptake and cytotoxicity for the Se nanospheres. Shifting focus to a bi-metallic system, I employed Pd cubic nanocrystals as templates to direct the surface deposition of Rh in a layer-by-layer manner. With rigorous regulation of the reaction kinetics, I successfully synthesized Pd@Rh nanocrystals featuring smooth, well-defined {100} facets and large sizes. The strong Rh−Rh binding within the shell imparted exceptional thermal stability to the core–shell nanocubes. Afterwards, chemical wet etching was employed to fabricate Rh nanocages with well-defined {100} surface and ultrathin walls from the core–shell nanocubes. Building upon these insights, I extended the two strategies to control the composition of complex alloys. By utilizing well-defined and highly stable Rh cubic nanocrystals as templates, together with a tight control over the reduction kinetics through dropwise injection of the precursor mixture, cubic-shaped nanocrystals featuring a nearly equimolar RuRhPdPt alloy surface were obtained. These alloy nanocubes demonstrated superior thermal stability in terms of both shape and composition, along with enhanced catalytic performance toward ethanol oxidation.
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Date Issued
2023-07-24
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Dissertation