Atomic mystery solved: graphite and water don't mix, and this is important for biomedical sensors or decontamination

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Life, often, is a matter of perspective. A problem isn't so bad when viewed from a different angle. If we apply this to science, the effect is amplified: what might seem irrelevant from a distance becomes crucial when observations are made at the scale of the smallest units of a solid: molecules and atoms. This is the case with the relationship between water and hydrophobic solid materials: their interaction has occupied scientific teams worldwide for decades. Now, a study recently published in Nature Communications has turned our understanding of the subject on its head and resolved existing controversies.

The research team has studied the interaction of water molecules on graphite under real environmental conditions and has discovered that water "never gets to the surface of the material, as it is interposed by two or three monolayers of hydrocarbons from the environment, which completely conditions the final properties of the material," explains Ricardo García, a CSIC researcher at the Madrid Institute of Materials Science and one of the leaders of the work.

The researcher points out that understanding how water interacts (and changes its structure) when it comes into contact with solid surfaces is key to many technological processes: “The ability to identify the realistic structure of solid-water interfaces is crucial for the rational design of systems used for energy conversion and storage or biodetection,” he explains. However, studying these interactions under real-world conditions is currently a significant challenge: the structure of water can be affected by many factors, and its study “is inherently complex.” Although several techniques have been developed to attempt this, none have yet fully explained the observed phenomena.

Now, thanks to a combination of advanced atomic force microscopy (AFM) and Raman spectroscopy (the study of the interaction between light and matter), they have been able to observe precisely, at the atomic level, what happens when water molecules reach graphite. “That hydrocarbon, which would normally be irrelevant, affects its surface at the molecular level and changes its properties,” continues García, who emphasizes that this explains “phenomena that previously didn't make sense, such as why a decontamination membrane was slower than expected.”

The researcher emphasizes that the discovery was made possible by the development of three-dimensional atomic force microscopy, a technique in which his laboratory at the ICMM-CSIC is a world leader. It is based on the interaction of an extremely fine tip (just a few atoms in size) with the liquid medium surrounding the surface of a material. Thanks to this technique, researchers can not only see the atoms but also interact with them with unprecedented precision.

Water vs. Carbon

The study, which has been selected as one of the most outstanding among those published by Nature Communications in recent months, analyzed the interaction between water and graphite because water-carbon interfaces (graphite being one of the forms in which carbon occurs in nature) are among the most important for applications such as energy storage, electrocatalysis, biodetection of contaminants, and water desalination. “Furthermore, we used a system that guarantees reproducible measurements in different laboratories,” he adds, regarding the relevance and replicability of his study.

Once they observed what was happening and why it affected applications, the authors of the study hoped the results would be applicable to other interactions between water and solids. “Most solid materials, such as semiconductors or metals, can increase their hydrophobicity when exposed to air. Now we know that, in those cases, a hydrocarbon barrier comes between their surface and the water,” they concluded.

Referencia Bibliográfica:
Lalith Krishna Samanth Bonagiri, Diana M. Arvelo, Fujia Zhao, Jaehyeon Kim, Qian Ai, Shan Zhou, Kaustubh S. Panse, Ricardo Garcia* & Yingjie Zhang*. Probing the molecular structure at graphite–water interfaces by correlating 3D-AFM and SHINERS. Nature Communications. DOI: https://doi.org/10.1038/s41467-026-68667-y