At the boundary between matter and environment—just a few atomic layers thick—the fate of a material is often decided. Researchers at the University of Potsdam and Fraunhofer IAP have turned to X-ray photoelectron spectroscopy to read the hidden chemistry of bio-based hybrid materials made from coffee grounds and orange peels, seeking to understand why some formulations purify water while others fall short. By mapping the outermost nanometers of these complex surfaces, they are translating the unpredictable richness of natural waste into the precise, reproducible language that industry require