title: Amino Acid-Based Stabilization of Oxide Nanocrystals in Polar Media: From Insight in Ligand Exchange to Solution ¹H NMR Probing of Short-Chained Adsorbates.
abstract: Ligand exchange is a crucial step between nanocrystal synthesis and nanocrystal application. Although colloidal stability and ligand exchange in nonpolar media are readily established, the exchange of native, hydrophobic ligands with polar ligands is less systematic. In this paper, we present a versatile ligand exchange strategy for the phase transfer of carboxylic acid capped HfO2 and ZrO2 nanocrystals to various polar solvents, based on small amino acids as the incoming ligand. To gain insight in the fundamental mechanism of the exchange, we study this system with a combination of FTIR, zeta potential measurements, and solution (1)H NMR techniques. The detection of surface-associated, small ligands with solution NMR proves challenging in this respect. Tightly bound amino acids are undetectable, but their existence can be proven through displacement with other ligands in titration experiments. Alternatively, we find that methyl moieties belonging to bound species can circumvent these limitations because of their more favorable relaxation properties as a result of internal mobility. As such, our results are not limited to amino acids but to any short-chained ligand and will therefore facilitate the rigorous investigation and understanding of various ligand exchange processes.
authors: Sol-Gel Center for Research on Inorganic Powders and Thin films Synthesis (SCRiPTS), ‡Physics and Chemistry of Nanostructures group (PCN), §NMR and Structure Analysis Unit (NMRSTR), ∥Center for Nano and Biophotonics, Ghent University , 9000 Ghent, Belgium.
authors: Jonathan
authors: J
authors: De Roo
authors: Sol-Gel Center for Research on Inorganic Powders and Thin films Synthesis (SCRiPTS), ‡Physics and Chemistry of Nanostructures group (PCN), §NMR and Structure Analysis Unit (NMRSTR), ∥Center for Nano and Biophotonics, Ghent University , 9000 Ghent, Belgium.
authors: Sofie
authors: S
authors: Coucke
authors: Sol-Gel Center for Research on Inorganic Powders and Thin films Synthesis (SCRiPTS), ‡Physics and Chemistry of Nanostructures group (PCN), §NMR and Structure Analysis Unit (NMRSTR), ∥Center for Nano and Biophotonics, Ghent University , 9000 Ghent, Belgium.
authors: Hannes
authors: H
authors: Rijckaert
authors: Sol-Gel Center for Research on Inorganic Powders and Thin films Synthesis (SCRiPTS), ‡Physics and Chemistry of Nanostructures group (PCN), §NMR and Structure Analysis Unit (NMRSTR), ∥Center for Nano and Biophotonics, Ghent University , 9000 Ghent, Belgium.
authors: Katrien
authors: K
authors: De Keukeleere
authors: Sol-Gel Center for Research on Inorganic Powders and Thin films Synthesis (SCRiPTS), ‡Physics and Chemistry of Nanostructures group (PCN), §NMR and Structure Analysis Unit (NMRSTR), ∥Center for Nano and Biophotonics, Ghent University , 9000 Ghent, Belgium.
authors: Davy
authors: D
authors: Sinnaeve
authors: Sol-Gel Center for Research on Inorganic Powders and Thin films Synthesis (SCRiPTS), ‡Physics and Chemistry of Nanostructures group (PCN), §NMR and Structure Analysis Unit (NMRSTR), ∥Center for Nano and Biophotonics, Ghent University , 9000 Ghent, Belgium.
authors: Zeger
authors: Z
authors: Hens
authors: Sol-Gel Center for Research on Inorganic Powders and Thin films Synthesis (SCRiPTS), ‡Physics and Chemistry of Nanostructures group (PCN), §NMR and Structure Analysis Unit (NMRSTR), ∥Center for Nano and Biophotonics, Ghent University , 9000 Ghent, Belgium.
authors: José C
authors: JC
authors: Martins
authors: Sol-Gel Center for Research on Inorganic Powders and Thin films Synthesis (SCRiPTS), ‡Physics and Chemistry of Nanostructures group (PCN), §NMR and Structure Analysis Unit (NMRSTR), ∥Center for Nano and Biophotonics, Ghent University , 9000 Ghent, Belgium.
authors: Isabel
authors: I
authors: Van Driessche