Regensburg 2025 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 4: Solid-Liquid Interfaces: Structure
O 4.9: Vortrag
Montag, 17. März 2025, 12:30–12:45, H4
Resolving the water structure at iron-oxide/water interface — •Harsharan Kaur1, Moritz Zelenka1,2, and Ellen Backus1,2 — 1University of Vienna, Faculty of Chemistry, Institute of Physical Chemistry, Währinger Str. 42, 1090 Vienna, Austria — 2University of Vienna, Vienna Doctoral School in Chemistry (DoSChem), Währinger Str. 42, 1090 Vienna, Austria
Among different iron-oxide polymorphs, Fe3O4 is utilized as a catalyst for industrial-gas shift and photocatalytic water splitting reactions, where it often encounters water. [1] Fe3O4 surface is known to protonate and deprotonate on contact with pH-variant aqueous media. [1] However, less is known about the interfacial species and their molecular orientation under ambient condition. Herein, we explore these attributes at the magnetite-water interface as function of solution pH with macroscopic amount of water. Magnetite films of ~50 nm thick were prepared using magnetron sputtering and were found to sustain Fe3O4 phase combined with FeO or γ-Fe2O3 state. The interface was examined with SFG vibrational spectroscopy. Due to its selection rule, a vibrational spectrum of only the interfacial species is obtained in case of centrosymmetric bulk materials like Fe3O4 and water. We observed a pH-dependent variation in the H-bonding strength of the interfacial water molecules and the presence of Fe-OH groups at alkaline pH. Besides, the water orientation varies with pH. By comparing the results for Fe3O4 to Fe2O3, a detailed molecular picture of interfacial water at these relevant iron oxides will be presented. [1]. Z. Bielan, S. Dudziak, A. Kubiak, E. Kowalska, Appl. Sci. 11 (2021) 10160.
Keywords: water structure; interface; molecular orientation; iron oxides; surface hydroxylation