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Item type:Publication, Access status: with files , Revealing formic acid adsorption geometries on magnetite (001) and (111) surfaces by IRRAS line shape analysis(RSC Publ, 2026-05-05); ; ; The sign and intensity of infrared (IR) bands on oxide surfaces strongly depend on light polarization and the adsorption geometry of surface species. In this study, we investigate formic acid adsorption on single crystalline magnetite Fe<inf>3</inf>O<inf>4</inf>(001) and Fe<inf>3</inf>O<inf>4</inf>(111) surfaces, which being neither perfect metals nor insulators exhibit characteristic Fano shaped IR line profiles. Using both s- and p-polarized infrared reflection absorption spectroscopy (IRRAS), we identify distinct spectral features and reveal vibrational bands that were previously unobserved in experiments employing unpolarized or solely p-polarized light. Complementary density functional theory (DFT) calculations provide structural and vibrational insights into the adsorbed species. On Fe<inf>3</inf>O<inf>4</inf>(001), a new band at 1555 cm<sup>−1</sup> observed with p-polarized light is attributed to the asymmetric OCO stretching vibration of formate bound to octahedral Fe sites with tetrahedral Fe<inf>tet1</inf> underneath. On Fe<inf>3</inf>O<inf>4</inf>(111), a band at 1730 cm<sup>−1</sup> detected in both unpolarized and s-polarized light corresponds to the CO stretch of a monodentate species. These results highlight the crucial role of light polarization in IRRAS for elucidating adsorption geometries and electronic properties of oxide surfaces.Publicationtype: Journal Article18 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Adsorption and Inactivation of SARS-CoV-2 on the Surface of Anatase TiO2(101)(Soc., 2023-02-15); ; ; ; We investigated the adsorption of severe acute respiratory syndrome corona virus 2 (SARS-CoV-2), the virus responsible for the current pandemic, on the surface of the model catalyst TiO2(101) using atomic force microscopy, transmission electron microscopy, fluorescence microscopy, and X-ray photoelectron spectroscopy, accompanied by density functional theory calculations. Three different methods were employed to inactivate the virus after it was loaded on the surface of TiO2(101): (i) ethanol, (ii) thermal, and (iii) UV treatments. Microscopic studies demonstrate that the denatured spike proteins and other proteins in the virus structure readsorb on the surface of TiO2 under thermal and UV treatments. The interaction of the virus with the surface of TiO2 was different for the thermally and UV treated samples compared to the sample inactivated via ethanol treatment. AFM and TEM results on the UV-treated sample suggested that the adsorbed viral particles undergo damage and photocatalytic oxidation at the surface of TiO2(101) which can affect the structural proteins of SARS-CoV-2 and denature the spike proteins in 30 min. The role of Pd nanoparticles (NPs) was investigated in the interaction between SARS-CoV-2 and TiO2(101). The presence of Pd NPs enhanced the adsorption of the virus due to the possible interaction of the spike protein with the NPs. This study is the first investigation of the interaction of SARS-CoV-2 with the surface of single crystalline TiO2(101) as a potential candidate for virus deactivation applications. Clarification of the interaction of the virus with the surface of semiconductor oxides will aid in obtaining a deeper understanding of the chemical processes involved in photoinactivation of microorganisms, which is important for the design of effective photocatalysts for air purification and self-cleaning materials.Publicationtype: Journal Article47 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Adsorption of oleic acid on magnetite facets(Macmillan Publishers Limited, part of Springer Nature, 2022-10-22); ; ; ; The microscopic understanding of the atomic structure and interaction at carboxylic acid/oxide interfaces is an important step towards tailoring the mechanical properties of nanocomposite materials assembled from metal oxide nanoparticles functionalized by organic molecules. We have studied the adsorption of oleic acid (C17H33COOH) on the most prominent magnetite (001) and (111) crystal facets at room temperature using low energy electron diffraction, surface X-ray diffraction and infrared vibrational spectroscopy complemented with molecular dynamics simulations used to infer specific hydrogen bonding motifs between oleic acid and oleate. Our experimental and theoretical results give evidence that oleic acid adsorbs dissociatively on both facets at lower coverages. At higher coverages, the more pronounced molecular adsorption causes hydrogen bond formation between the carboxylic groups, leading to a more upright orientation of the molecules on the (111) facet in conjunction with the formation of a denser layer, as compared to the (001) facet. This is evidenced by the C=O double bond infrared line shape, in depth molecular dynamics bond angle orientation and hydrogen bond analysis, as well as X-ray reflectivity layer electron density profile determination. Such a higher density can explain the higher mechanical strength of nanocomposite materials based on magnetite nanoparticles with larger (111) facets.Publicationtype: Journal ArticleScopus© Citations 2 68 210 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Surface structure of magnetite (111) under oxidizing and reducing conditions(IOP Publishing, 2022-02-22); ; ; ; We report on differences in the magnetite (111) surface structure when prepared under oxidizing and reducing conditions. Both preparations were done under UHV conditions at elevated temperatures, but in one case the sample was cooled down while keeping it in an oxygen atmosphere. Scanning tunneling microscopy after each of the preparations showed a different apparent morphology, which is discussed to be an electronic effect and which is reflected in the necessity of using opposite bias tunneling voltages in order to obtain good images. Surface x-ray diffraction revealed that both preparations lead to Fe vacancies, leading to local O-terminations, the relative fraction of which depending on the preparation. The preparation under reducing conditions lead to a larger fraction of Fe-termination. The geometric structure of the two different terminations was found to be identical for both treatments, even though the surface and near-surface regions exhibit small compositional differences; after the oxidizing treatment they are iron deficient. Further evidence for the dependence of iron vs oxygen fractional surface terminations on preparation conditions comes from Fourier transform infrared reflection-absorption spectroscopy, which is used to study the adsorption of formic acid. These molecules dissociate and adsorb in chelating and bidentate bridging geometries on the Fe-terminated areas and the signal of typical infrared absorption bands is stronger after the preparation under reducing conditions, which results in a higher fraction of Fe-termination. The adsorption of formic acid induced an atomic roughening of the magnetite (111) surface which we conclude from the quantitative analysis of the crystal truncation rod data. The roughening process is initiated by atomic hydrogen, which results from the dissociation of formic acid after its adsorption on the surface. Atomic hydrogen adsorbs at surface oxygen and after recombination with another H this surface hydroxyl can form H2O, which may desorb from the surface, while iron ions diffuse into interstitial sites in the bulk.Publicationtype: Journal ArticleScopus© Citations 10 73 336 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Heterogeneous adsorption and local ordering of formate on a magnetite surface(2021-04-22); ; ; ; We report a novel heterogeneous adsorption mechanism of formic acid on the magnetite (111) surface. Our experimental results and density functional theory (DFT) calculations give evidence for dissociative adsorption of formic acid in quasibidentate and chelating geometries. The latter is induced by the presence of iron vacancies at the surface, making oxygen atoms accessible for hydrogen atoms from dissociated formic acid. DFT calculations predict that both adsorption geometries are energetically favorable under our experimental conditions. The calculations prove that the locally observed (√3 × √3)R 30° superstructure consists of three formate molecules in a triangular arrangement, adsorbed predominantly in a chelating geometry. The results show how defects can stabilize alternative adsorption geometries, which is a crucial ingredient for a detailed atomistic understanding of reaction barriers on magnetite and other oxide surfaces, as well as for the stability of carboxylic acid based nanocomposite materials.Publicationtype: Journal ArticleScopus© Citations 8 173 578 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Carboxylic acid induced near-surface restructuring of a magnetite surface(Macmillan Publishers Limited, part of Springer Nature, 2019-08-09); ; ; ; A fundamental knowledge of the interaction of carboxylic acids, such as formic acid, with magnetite surfaces is of prime importance for heterogeneous catalysis and the synthesis of novel materials. Despite this, little is known about the atomic scale adsorption mechanisms. Here we show by in-situ surface X-ray diffraction that the oxygen rich subsurface cation vacancy reconstruction of the clean magnetite (001) surface is lifted by dissociative formic acid adsorption, reestablishing a surface with bulk stoichiometry. Using density functional theory, the bulk terminated, fully formic acid covered surface is calculated to be more stable than the corresponding clean, reconstructed surface. A comparison of calculated and experimental infrared bands supports the bidentate adsorption geometry and a specific adsorption site. Our results pave the way for a fundamental understanding of the bonding mechanism at carboxylic acid/oxide interfaces.Publicationtype: Journal ArticleScopus© Citations 16 402 349