The Chemical Environments of Oleate Species within Samples of Oleate-Coated PbS Quantum Dots
- 20 June 2013
- journal article
- Published by American Chemical Society (ACS) in Analytical Chemistry
- Vol. 85 (14), 6974-6979
- https://doi.org/10.1021/ac401623a
Abstract
A combination of FT-IR, 1H NMR, nuclear Overhauser effect (NOESY), and diffusion-ordered (DOSY) NMR spectroscopies shows that samples of oleate-coated PbS quantum dots (QDs) with core radii ranging from 1.6 to 2.4 nm, and purified by washing with acetone, contain two species of oleate characterized by the stretching frequencies of their carboxylate groups, the chemical shifts of their protons, and their diffusion coefficients. One of these oleate species exists primarily on the surfaces of the QDs and either chelates a Pb2+ ion or bridges two Pb2+ ions. The ratio of bridging oleates to chelating oleates on the surfaces of the QDs is approximately 1:1 for all sizes of the QDs we studied. The second oleate species in these samples bridges two Pb2+ ions within clusters or oligomers of lead oleate (with a hydrodynamic radius of ∼1.4 nm), which are byproducts of the QD synthesis. The concentration of these clusters increases with increasing size of the QDs because larger QDs are produced by increasing the concentration of the oleic acid ligand in the reaction mixture. The oleate molecules on the surfaces of the QDs and within the lead oleate clusters are in rapid exchange with each other. Additional washes with methanol progressively eliminate the contaminating clusters from the PbS QD samples. This work quantitatively characterizes the distribution of binding geometries at the inorganic/organic interface of the nanocrystals and demonstrates the utility of using organic ligands as probes for the composition of a colloidal QD sample as a function of the preparation procedure.Keywords
This publication has 30 references indexed in Scilit:
- Gating of hole transfer from photoexcited PbS quantum dots to aminoferrocene by the ligand shell of the dotsChemical Communications, 2012
- Passivating ligand and solvent contributions to the electronic properties of semiconductor nanocrystalsNanoscale, 2012
- Simultaneous Determination of the Adsorption Constant and the Photoinduced Electron Transfer Rate for a Cds Quantum Dot–Viologen ComplexJournal of the American Chemical Society, 2011
- Utilizing Self-Exchange To Address the Binding of Carboxylic Acid Ligands to CdSe Quantum DotsJournal of the American Chemical Society, 2010
- Surface Chemistry of Colloidal PbSe NanocrystalsJournal of the American Chemical Society, 2008
- Ligand Adsorption/Desorption on Sterically Stabilized InP Colloidal Nanocrystals: Observation and Thermodynamic AnalysisChemphyschem, 2006
- In Situ 1H NMR Study on the Trioctylphosphine Oxide Capping of Colloidal InP NanocrystalsChemphyschem, 2005
- Effect of the Thiol−Thiolate Equilibrium on the Photophysical Properties of Aqueous CdSe/ZnS Nanocrystal Quantum DotsJournal of the American Chemical Society, 2005
- PbS Quantum Dots with Stable Efficient Luminescence in the Near‐IR Spectral RangeAdvanced Materials, 2004
- Colloidal PbS Nanocrystals with Size‐Tunable Near‐Infrared Emission: Observation of Post‐Synthesis Self‐Narrowing of the Particle Size DistributionAdvanced Materials, 2003