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A Combined SAXS/SANS Study for the in Situ Characterization of Ligand Shells on Small Nanoparticles: The Case of ZnO
journal contribution
posted on 2015-09-22, 00:00 authored by T. Schindler, M. Schmiele, T. Schmutzler, T. Kassar, D. Segets, W. Peukert, A. Radulescu, A. Kriele, R. Gilles, T. UnruhZnO nanoparticles (NPs) have great
potential for their use in,
e.g., thin film solar cells due to their electro-optical properties
adjustable on the nanoscale. Therefore, the production of well-defined
NPs is of major interest. For a targeted production process, the knowledge
of the stabilization layer of the NPs during and after their formation
is of particular importance. For the study of the stabilizer layer
of ZnO NPs prepared in a wet chemical synthesis from zinc acetate,
only ex situ studies have been performed so far. An acetate layer
bound to the surface of the dried NPs was found; however, an in situ
study which addresses the stabilizing layer surrounding the NPs in
a native dispersion was missing. By the combination of small angle
scattering with neutrons and X-rays (SANS and SAXS) for the same sample,
we are now able to observe the acetate shell in situ for the first
time. In addition, the changes of this shell could be followed during
the ripening process for different temperatures. With increasing size
of the ZnO core (dcore) the surrounding
shell (dshell) becomes larger, and the
acetate concentration within the shell is reduced. For all samples,
the shell thickness was found to be larger than the maximum extension
of an acetate molecule with acetate concentrations within the shell
below 50 vol %. Thus, there is not a monolayer of acetate molecules
that covers the NPs but rather a swollen shell of acetate ions. This
shell is assumed to hinder the growth of the NPs to larger macrostructures.
In addition, we found that the partition coefficient μ between
acetate in the shell surrounding the NPs and the total amount of acetate
in the solution is about 10% which is in good agreement with ex situ
data determined by thermogravimetric analysis.
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thermogravimetric analysischemical synthesisstabilizer layeracetate ionsacetate shellZnO coreSmall NanoparticlesSitu CharacterizationSAXSpartition coefficient μacetate moleculesproduction processacetate concentrationstabilization layeracetate moleculezinc acetateZnO NPsSANSLigand Shellsacetate layershell thicknessZnOZnO nanoparticlesacetate concentrations
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