Effects of Crosslinking Density in the Formation of Gold-Polymer Composite Particles and Their Catalytic Applications
Date of Award
Master of Science (MS)
Department of Chemistry
Nanoscale metal particles have been extensively fabricated to serve as catalysts for various organic reactions due to their large surface areas, tunable structural changes, and easy recyclability. Although diverse synthetic strategies have achieved great progress in designing catalytically active metal nanoparticles, a major concern in most synthetic methods is the inevitable use of stabilizing and/or capping agents to prepare the colloidal form of metal nanoparticles against their aggregation in solution unless they are supported onto stable substrates. However, the presence of stabilizing agents around metal nanoparticles for catalytic applications can often minimize and block the readily available active sites of metal surfaces, which can greatly reduce their catalytic performance. We prepared surfactant-free and physically-incorporated gold nanoparticles (AuNPs) within poly(N-isopropylacrylamide), PNIPAM, particles in situ via a light-induced reduction method. The polymer particles did not possess any functional groups to induce strong interactions, but still provided a highly improved stability to the embedded AuNPs, which were tested as quasi-homogenous catalysts in carbon-carbon forming reactions in pure alcohol and alcohol-rich aqueous solvents under ambient aerobic conditions. The light-induced reduction of gold ions in the presence of the PNIPAM particles in situ resulted in the effective formation of composite particles physically loaded with AuNPs. To further examine the relationships between the density (e.g., free volume) of the PNIPAM network and catalytic reactivity of the incorporated AuNPs, PNIPAM particles possessing various degrees of crosslinking density were prepared and used as host particles during the in situ reduction of gold ions. The structural features and loading efficiency of the guest AuNPs were thoroughly evaluated as a function of the crosslinking density. The resulting composite particles were also employed as quasi-homogeneous catalysts in C-C forming homocoupling reactions. Furthermore, optimum reaction conditions were established by screening various solvents, bases, temperatures, and recyclability using these composite particles, which were also applied to the homocoupling of other arylboronic acid reactants. Investigating the influence of host polymer particle networks on the structural and catalytic properties of the guest metal nanoparticles as well as ideal reaction conditions will lead to the development of robust and industrially practical catalytic systems.
Egemole, Franklin Obinna, "Effects of Crosslinking Density in the Formation of Gold-Polymer Composite Particles and Their Catalytic Applications" (2021). Theses and Dissertations. 1433.
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