irect air capture (DAC) of CO2 is a potential strategy for capturing CO2 for later geological sequestration. A potentially promising DAC technique is mineral looping using MgO in which the CO2 reacts with the MgO to form a magnesium carbonate phase. However, passivation of the surface by hydrated carbonate phases may limit the carbon capture potential. Doping MgO with impurities (e.g., Fe, Li or Co) may inhibit this passivation. Here we use two synchrotron x-ray scattering techniques, low angle x-ray reflectivity (XRR) and crystal truncation rod (CTR) measurements, interpreted with the aid of classical molecular dynamics simulations to understand how the hydration structure of the MgO(100) as compared with Fe-doped MgO(100) evolves upon exposure to humidity. The initial film that forms on the both samples grows rapidly for a short time (seconds-to-minutes) upon exposure to humid nitrogen. As compared with the pure MgO sample, the hydrated film on the Fe-doped MgO is thinner and grows slower upon exposure to humid nitrogen. This suggests doping of samples may affect the hydration reactions at the MgO surface, which may have further implications for the carbonation reactions. A potential mechanism of hydration reactions might be revealed from CMD simulations where oxygens on interfacial water coordinate surface magnesiums and hydrogens on the same molecules are donating hydrogen bonds at neighboring surface oxygen surface sites on the MgO. This orientation suggests a facile water coordination environment for hydroxlyation of the MgO.

Inhibition of hydrated film formation on MgO

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