Structure and Chemical Composition of Soil C‑Rich Al–Si–Fe Coprecipitates at Nanometer Scale

• Published in: Environmental science & technology Vol. 57; no. 49; pp. 20615 - 20626
• Main Authors: Jamoteau, Floriane, Cam, Nithavong, Levard, Clément, Doelsch, Emmanuel, Gassier, Ghislain, Duvivier, Adrien, Boulineau, Adrien, Saint-Antonin, François, Basile-Doelsch, Isabelle
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 12.12.2023
• Subjects: Agricultural sciences; Aluminum; Andosols; Atomic structure; Biogeochemical Cycling; Carbon; Carbon sequestration; Chemical composition; Chemical extraction; Electron energy loss spectroscopy; energy; Energy loss; environmental science; Environmental Sciences; Image resolution; Iron; Life Sciences; Microscopy, Electron, Transmission; Minerals; Minerals - chemistry; nanomaterials; Organic matter; sediments; Short range order; Silicon; skeleton; Soil - chemistry; soil carbon; Soil stabilization; Soil study; Spectroscopy; Stabilization; Transmission electron microscopy; X-radiation; soil carbon cycle; EELS; organic matter; coprecipitates; EDX; organo-mineral associations; transmission electron microscopy; Soil carbon cycle
• ISSN: 0013-936X; 1520-5851; 1520-5851
• DOI: 10.1021/acs.est.3c06557

Soil carbon stabilization is mainly driven by organo-mineral interactions. Coprecipitates, of organic matter with short-range order minerals, detected through indirect chemical extraction methods, are increasingly recognized as key carbon sequestration phases. Yet the atomic structure of these coprecipitates is still rather conceptual. We used transmission electron microscopy imaging combined with energy-dispersive X-ray and electron energy loss spectroscopy chemical mappings, which enabled direct nanoscale characterization of coprecipitates from Andosols. A comparison with reference synthetic coprecipitates showed that the natural coprecipitates were structured by an amorphous Al, Si, and Fe inorganic skeleton associated with C and were therefore even less organized than short-range order minerals usually described. These amorphous types of coprecipitates resembled previously conceptualized nanosized coprecipitates of inorganic oligomers with organics (nanoCLICs) with heterogeneous elemental proportions (of C, Al, Si, and Fe) at nanoscale. These results mark a new step in the high-resolution imaging of organo-mineral associations, while shedding further light on the mechanisms that control carbon stabilization in soil and more broadly in aquatic colloid, sediment, and extraterrestrial samples.