In situ imaging of amorphous intermediates during brucite carbonation in supercritical CO2

• Published in: Nature materials 2022-03, Vol.21 (3), p.345-351
• Main Authors: Zhang, Xin, Lea, Alan S., Chaka, Anne M., Loring, John S., Mergelsberg, Sebastian T., Nakouzi, Elias, Qafoku, Odeta, De Yoreo, James J., Schaef, Herbert T., Rosso, Kevin M.
• Format: Article
• Language: English
• Subjects: 119/118; 140/146; 639/301/357/551; 639/301/930/2735; 639/638/542/968; Biomaterials; Chemistry and Materials Science; Condensed Matter Physics; Materials Science; Nanotechnology; Optical and Electronic Materials
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/s41563-021-01154-5

Progress in understanding crystallization pathways depends on the ability to unravel relationships between intermediates and final crystalline products at the nanoscale, which is a particular challenge at elevated pressure and temperature. Here we exploit a high-pressure atomic force microscope to directly visualize brucite carbonation in water-bearing supercritical carbon dioxide (scCO 2 ) at 90 bar and 50 °C. On introduction of water-saturated scCO 2 , in situ visualization revealed initial dissolution followed by nanoparticle nucleation consistent with amorphous magnesium carbonate (AMC) on the surface. This is followed by growth of nesquehonite (MgCO 3 ·3H 2 O) crystallites. In situ imaging provided direct evidence that the AMC intermediate acts as a seed for crystallization of nesquehonite. In situ infrared and thermogravimetric–mass spectrometry indicate that the stoichiometry of AMC is MgCO 3 · x H 2 O ( x  = 0.5–1.0), while its structure is indicated to be hydromagnesite-like according to density functional theory and X-ray pair distribution function analysis. Our findings thus provide insight for understanding the stability, lifetime and role of amorphous intermediates in natural and synthetic systems. Non-classical crystallization may proceed through formation of intermediate phases, but it is not known whether these are linked to the final crystallization. Here, using an atomic force microscope at 90 bar, brucite carbonation is directly observed, with an amorphous intermediate acting as the seed for crystalline nesquehonite.