Proceedings of nanoGe Fall Meeting19 (NFM19)
DOI: https://doi.org/10.29363/nanoge.nfm.2019.120
Publication date: 18th July 2019
1-Octadecene is a widely used solvent for high temperature nanocrystal synthesis (120 – 320 °C). A good solvent should have a high boiling point and high stability. Decomposition of the solvent could potentially interfere with the synthesis or contaminate the nanocrystal product.
Here, we show that 1-octadecene spontaneously polymerizes at temperatures relevant for nanocrystal synthesis. Using Diffusion Order Spectroscopy (DOSY) NMR, we detect its presence in five different NC syntheses: ZnS:Mn, CuInS2, CdS, TiO2, and Fe3O4. The resulting poly(1-octadecene) has a comparable solubility and size to nanocrystals stabilized by hydrophobic ligands. As a result, typical purification procedures (precipitation/redispersion cycles or size exclusion chromatography) fail to separate the poly(1-octadecene) impurity from the nanocrystal product. To avoid formation of poly(1-octadecene), we replaced 1-octadecene with saturated, aliphatic solvents. Alternatively, the native ligands are exchanged for polar ligands, leading to significant solubility differences between nanocrystals and poly(1-octadecene), therefore allowing isolation of pure nanocrystals, free from polymer impurities.
In conclusion, the ubiquitous use of 1-octadecene for nanocrystal syntheses is questioned given its propensity to polymerise and contaminate the nanocrystal product. These results will help design superior syntheses and improve nanocrystal purity, an important factor in many applications.
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