Date on Master's Thesis/Doctoral Dissertation

12-2025

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemistry

Degree Program

Chemistry, PhD

Committee Chair

Zamborini, Francis

Committee Member

Buchanan, Robert

Committee Member

Wilson, Andrew J.

Committee Member

Ramezanipour, Farshid

Committee Member

Williams, Stewart

Author's Keywords

Nanoparticles; nanoclusters; catalysis; hydrogel beads; chemisorption; galvanic reaction

Abstract

This dissertation explores the synthesis, stability, and reactivity of various metal nanoparticles (NPs) and nanoclusters (NCs) of varied size and stabilizers contained within millimeter-sized calcium alginate (Ca-Alg) hydrogel polymer beads. Hydrogel beads synthesized by combining sodium alginate with Au or Ag NPs stabilized with trisodium citrate (Cit) and adding dropwise into a 4.0 M Ca2+ solution remained stable and contained within the beads. Those synthesized Au, Pd and AuPd NCs stabilized with glutathione (SG) became partially released from the hydrogel within a day. The synthesis of beads containing aggregated Cit Au NPs occurs by inducing aggregation with tetrakis(hydroxymethyl) phosphonium chloride (THPC) prior to bead formation. Cit metal NPs do not aggregate in the presence THPC when inside the bead after bead formation, however, iodine induced aggregation occurs for SG Au NCs within the beads, but only with a small amount of ethanol added to the aqueous iodine solution. Hydrogel beads containing Cit Au NPs surface are available for chemical binding and functionalization. For a constant Au volume, beads with 4 nm Cit Au NPs adsorbed more 4-NTP and at a faster rate than 15 nm Cit Au NPs, consistent with the higher surface area to volume ratio for smaller Au NPs. In another example of reactivity, beads containing Cit Ag NPs reacted with AuCl4- by galvanic replacement inside the hydrogel beads. The rate increased approximately first order with AuCl4- concentration and visibly occurred inside the bead by observation of a unique Ag core/Au shell bead structure. Finally, various beads containing Cit Au NPs successfully catalyzed the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) but this only occurs inside the beads when excess Ca2+ crosslinker is in the reaction mixture. Otherwise, small amount of Au NPs release from the beads and catalyze the reaction outside of the hydrogel beads. Importantly, the reaction rate increases with each catalyst cycle with Ca2+ in the solution and the stability was good enough to reuse the hydrogel beads catalysts at least 30 times. The reaction rate was faster with the beads containing 4 nm Au NPs compared to those containing 15 nm Au NPs. Controlling the synthesis of hydrogel beads containing metal nanostructures and gaining better fundamental understanding of their reactivity may lead to their use in various applications, including sensing, catalysis, and biomedical therapy/diagnostics.

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