CO2 Chemisorption and Exfoliation of a Crystalline Ammonium-Carbamate and the Corresponding n-Alkylamine

Le résumé fourni par la source

CO 2 capture from ambient air by crystalline alkylamines, leading to the corresponding crystalline ammonium-carbamates, was already reported in the literature. In this paper, for the first time, we show that these layered crystalline structures can be fully exfoliated with a complete loss of order perpendicular to the structural bilayers and with the maintenance of crystalline order in the structural bilayers. Exfoliation of octadecylammonium-octadecylcarbamate (OAOC), as obtained by CO 2 chemisorption from octadecylamine (ODA), spontaneously occurs after long-term room temperature aging as well as by ball-milling of OAOC crystalline powder at high spinning rates. Moreover, a full exfoliation of ODA can be achieved by high-temperature decarbonation of crystalline OAOC in the range of 80–100 °C. Wide-angle X-ray Diffraction (WAXD) profiles of exfoliated OAOC and ODA have been modeled, by using small clusters of chains belonging to isolated structural bilayers, reaching a good agreement between experimental and calculated profiles. Scanning electron microscopy (SEM) analysis shows that the observed exfoliation phenomena are generally associated with the formation of plate-like crystalline morphologies. Differential scanning calorimetry (DSC) scans of exfoliated OAOC exhibit well-separated melting peak (located at 95 °C) and decarbonation peak (roughly centered at 102 °C). Additionally, this study shows that carbonation reactions in ambient air are faster for exfoliated ODA than for crystalline ODA.

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