Browsing by Author "Clark, Benjamin D."

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    Ligand-Dependent Colloidal Stability Controls the Growth of Aluminum Nanocrystals
    (American Chemical Society, 2019) Clark, Benjamin D.; DeSantis, Christopher J.; Wu, Gang; Renard, David; McClain, Michael J.; Bursi, Luca; Tsai, Ah-Lim; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics
    The precise size- and shape-controlled synthesis of monodisperse Al nanocrystals remains an open challenge, limiting their utility for numerous applications that would take advantage of their size and shape-dependent optical properties. Here we pursue a molecular-level understanding of the formation of Al nanocrystals by titanium(IV) isopropoxide-catalyzed decomposition of AlH3ﾠin Lewis base solvents. As determined by electron paramagnetic resonance spectroscopy of intermediates, the reaction begins with the formation of Ti3+-AlH3ﾠcomplexes. Proton nuclear magnetic resonance spectroscopy indicates isopropoxy ligands are removed from Ti by Al, producing aluminum(III) isopropoxide and low-valent Ti3+ﾠcatalysts. These Ti3+ﾠspecies catalyze elimination of H2ﾠfrom AlH3ﾠinducing the polymerization of AlH3ﾠinto colloidally unstable low-valent aluminum hydride clusters. These clusters coalesce and grow while expelling H2ﾠto form colloidally stable Al nanocrystals. The colloidal stability of the Al nanocrystals and their size is determined by the molecular structure and density of coordinating atoms in the reaction, which is controlled by choice of solvent composition.
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    Polydopamine-Stabilized Aluminum Nanocrystals: Aqueous Stability and Benzo[a]pyrene Detection
    (American Chemical Society, 2019) Renard, David; Tian, Shu; Ahmadivand, Arash; DeSantis, Christopher J.; Clark, Benjamin D.; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics
    Aluminum nanocrystals have emerged as an earth-abundant material for plasmonics applications. Al nanocrystals readily oxidize in aqueous-based solutions, however, transforming into highly stratified γ-AlOOH nanoparticles with a 700% increase in surface area in a matter of minutes. Here we show that by functionalizing Al nanocrystals with the bioinspired polymer polydopamine, their stability in aqueous media is dramatically increased, maintaining their integrity in aqueous solution for over 2 weeks with no discernible structural changes. Polydopamine functionalization also provides a molecular capture layer that enables the capture of polycyclic aromatic hydrocarbon pollutants in H2O samples and their detection by surface-enhanced Raman spectroscopy, when polydopamine-stabilized Al nanocrystal aggregates are used as substrates. This approach was used to detect a prime carcinogenic H2O pollutant, benzo[a]pyrene with a sensitivity in the sub part-per-billion range.