Interfacial diffusion of water and organic molecules on surfaces of iron-oxide nanoparticles

 

Iron-oxide nanoparticles (NP) and related mixed metal ferrites are of increasing interest in e.g. heterogeneous catalysis or biomedicine, and solid-liquid interfaces are omnipresent in many applications. Yet the experimental characterization of these interfaces is challenging, since the contribution of the volume signal often dominates the interfacial signal. Via pair distribution function analysis of X-ray scattering data we achieved insight into the structure of restructured hydration shells around 7 – 15 nm sized iron oxide NPs. Since restructuring comes along with modified dynamic properties, this project shall complement our structural studies with dynamical insight.

Relaxation times of rotational and translational diffusion of water molecules around ions in solution differ from the corresponding times in bulk water. Hence, modified dynamical properties of water molecules are also to be expected at NP surfaces. With quasielastic neutron scattering (QENS), we can measure dynamical properties of single molecules in spatial and time domain on time scales of 10-13 to 10-7 s, corresponding to typical relaxation times of diffusion processes. This project has the aim to establish QENS for the characterization of the dynamics of water and ligand molecules on surfaces of iron-oxide NPs. From the QENS data, we will be able to determine the different types of diffusion behavior of water and ligands molecules on the NPs, e.g. translational or rotational diffusional modes. Temperature-dependent measurements will allow us to access the activation energies of the motions. This project will enable a deeper understanding of the dynamics of water and ligand molecules around metal oxide NPs, relevant for nanomaterials, mineralogy or catalysis.

  QENS scheme Copyright: © MZ

The figure displays schematically the signal of an elastic line (blue curve) at a temperature T1, at which no dynamic processes occur. By increasing the temperature of the sample to T2 > T1, a dynamic process is excited, for instance the diffusion of a molecule on a surface. This diffusional process produces a quasielastic signal, which is the broadened contribution (red curve).

 

Team:

Prof. Dr. Mirijam Zobel
M. Sc. Anna Feghelm (PhD student)

Publications:

Eckardt, Mirco; Thomae, Sabrina L. J.; Dulle, Martin; Hörner, Gerald; Weber, Birgit; Förster, Stephan; Zobel, Mirijam*: Long-term colloidally stable dispersions of 5 nm sized mixed metal ferrites. ChemistryOpen (2020), 9, 1214–1220; https://doi.org/10.1002/open.202000313

Thomä, Sabrina; Krauss, Sebastian W.; Eckardt, Mirco; Chater, Phil; Zobel, Mirijam*: Atomic insight into hydration shells around facetted nanoparticles. Nature Communications vol. 10 (2019) issue 1; https://doi.org/10.1038/s41467-019-09007-1

  DFG Copyright: © DFG

Funding:

Deutsche Forschungsgemeinschaft (DFG)
Title of project: Diffusion von Wasser-, Diethylenglykol- und Zitratmolekülen auf Eisenoxid-Nanopartikeloberflächen via Quasielastischer Neutronenstreuung
Grant Nr.: ZO 369/3-1