Sprecher
Beschreibung
Surface functionalization is needed for synthesizing and controlling the properties of iron oxide nanoparticles (IONPs) in various applications for biomedicine, ferrofluids, or heterogeneous catalysis [1,2]. Yet, experimental investigations of interfacial properties such as the dynamics of ligand and water molecules near the nanoparticle surface have been scarce. Previously, quasielastic neutron scattering (QENS) was successfully used to access the dynamics of water molecules on surfaces of TiO2 and SnO2 nanoparticles [3]. QENS studies of ligand dynamics on the surface of nanoparticles have also emerged recently. Dodecanethiol on PbS nanoparticles and oleates on IONPs were shown to exhibit rotational motion [4,5]. However, the dynamics of citrate ligands on the surface of magnetic IONPs are largely unknown. We report on QENS experiments on 6 nm IONPs synthesized according to ref [6] and equilibrated at 8 % relative humidity in H2O (measured at IN16B, ILL) and D2O (measured at Emu, ANSTO). Energy-resolved measurements as well as elastic and inelastic fixed window scans were performed in the temperature range of 2 – 380 K, covering a Q-range of 0.19 – 1.83 Å-1. Given the complex quasielastic scattering signal including the magnetic nature of the IONPs, we demonstrate the power of fixed window scans in separating multiple, dynamic processes, thermal vibrations, magnetic relaxations, and hydrogen dynamics. Employing samples equilibrated in D2O allowed for distinguishing water and citrate motion. To create a complete dynamical model, we implemented a simultaneous fit approach for elastic and inelastic fixed window scans, as well as energy-resolved spectra at different temperatures. We observed that the introduction of additional datasets into a simultaneous fit routine increases the stability of the fit, allowing for the application of more complex models. Further, the Q-dependence of energy-resolved spectra shows, that citrate molecules only exhibit a rotational motion on the IONPs surface, while water diffuses translationally.
[1] Y. Sahoo, et al., J Phys Chem B, 109, 3879–3885 (2005)
[2] E. Amstad, et al., Nanoscale, 3, 2819 (2011)
[3] E. Mamontov, et al., J. Phys. Chem. C, 111, 4328-41 (2007)
[4] M. Jansen, et al., ACS Nano, 12, 20517-20526 (2021)
[5] A. Sharma, et al., Chem. Phys., 156, 164908 (2022)
[6] M. Eckardt, et al., ChemistryOpen, 9, 1214–122 (2020)
