A chemical reaction in X-ray vision

Morphological characterization of the Fe₃S₄ nanosheet-like structures. (a,b) SEM images at different magnifications. (c) TEM image, evidencing the two-dimensional structure, (d) HRTEM image with the corresponding FFT pattern shown in the inset. (e,f) Magnified views of the boxed regions marked in blue and pink in (d), highlighting the crystallographic planes of Fe₃S₄. (g−i) Dark-field STEM image and the corresponding EDX elemental mapping of Fe (red) and S (yellow). (j) AFM image and corresponding height profile of a Fe₃S₄ nanosheet on a Si wafer. The dashed line indicates the region where the profile was measured. @JACS

Research team uses DESY’s PETRA III X-ray light source and ESRF to observe the formation of iron-sulphur nanosheets in real time for the first time

An international research team has gained fundamental insights into the formation of metastable materials. In the future, the results could assist in designing nanostructures in a specific way – for example, for more efficient energy storage devices, catalysts, or functional materials. Using time-resolved X-ray methods, the team from DESY, the European Synchrotron Radiation Facility (ESRF), the University of Hamburg, and the University of Toulouse made the entire reaction pathway leading to iron-sulphur nanostructures visible – from the molecular precursors to complete, ultrathin nanolayers. The researchers published their findings in the renowned Journal of the American Chemical Society (JACS).

Iron-sulphur compounds play an important role in geological processes and technological applications, such as research into energy-relevant materials. The mineral greigite (Fe₃S₄) is particularly interesting due to its exceptional magnetic and electronic properties. Despite intensive research, however, experts have so far been unclear about how such nanostructures actually arise in chemical synthesis.

An international team led by Dorota Koziej from the University of Hamburg and the Cluster of Excellence “CUI: Advanced Imaging of Matter” has succeeded in deciphering the previously hidden formation process as part of the ERC Consolidator Project LINCHPIN. To do this, the researchers combined several X-ray methods at the high-energy X-ray sources of the European Synchrotron Radiation Facility (ESRF) and DESY. Without the highly brilliant X-ray sources, the otherwise very weak signal would not have been measurable. While the reaction was taking place, they simultaneously observed the structure, the oxidation state of the iron, and the environment around the formation of the chemical bonds.

An unexpected intermediate step leads to the formation of a crumpled nanosheet

The measurements show that the desired material does not form directly. Instead, a short-lived, layer-like intermediate product made of iron sulphide is first formed. This grows preferentially in two dimensions and then passes on its crumpled nanolayer shape to the final material. In a conversion step, the atoms in the solid reorganise themselves without losing this characteristic crumpled nano-sheet form – a reaction that experts refer to as being topotactic.

“We were able to gain a very good overview of the individual steps of the reaction – from the initial reduction of the iron compound to the formation of the final iron-sulphur nanostructure,” says Cecilia Zito from the University of Hamburg. “Such detailed insights are only possible by combining several analytical methods at a synchrotron using specially developed measuring cells,” adds Lars Klemeyer, whose doctoral thesis at the University of Hamburg forms the basis for the publication.

Significance regarding materials design and natural processes

The research findings are significant far beyond the specific material system investigated. They show how much intermediate steps and growth dynamics determine the final form of nanomaterials. “We hope to gain decisive insights that will enable us to design nanostructures in a specified manner in the future – for example, for more efficient energy storage devices, catalysts or functional materials,” says co-author Ann-Christin Dippel from DESY.

At the same time, the experiments provide new clues as to how similar minerals may have formed in nature, such as in the oxygen-poor environments of the early Earth.

The work also highlights the potential of modern multimodal in situ X-ray analysis methods to decipher chemical processes at the molecular and nanoscale level over time – an approach that can be applied to many other material systems in the future.

Researchers such as Ann-Christin Dippel expect even more from the 4D X-ray microscope PETRA IV planned at DESY: “With the upgrade from PETRA III to PETRA IV, we hope in the future to be able to image individual nanoparticles in their atomic structure and observe their growth within the reaction environment.”

Reference

In situ X‑ray Synchrotron Studies Reveal the Nucleation and Topotactic Transformation of Iron Sulfide Nanosheets

Cecilia A. Zito, Lars Klemeyer, Francesco Caddeo, Brian Jessen, Sani Y. Harouna-Mayer, Lise-Marie Lacroix, Malte Langfeldt, Tjark L. R. Gröne, Jagadesh K. Kesavan, Chia-Shuo Hsu, Alexander Schwarz, Ann-Christin Dippel, Fernando Igoa Saldaña, Blanka Detlefs, and Dorota Koziej

J. Am. Chem. Soc. 147, 47409−47420 (2025)

DOI: 10.1021/jacs.5c15843

Source: Universität Hamburg