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Bracco JN, Camacho Meneses G, Colón O, Yuan K, Stubbs JE, Eng PJ, Wanhala AK, Einkauf JD, Boebinger MG, Stack AG, Weber J. Reaction Layer Formation on MgO in the Presence of Humidity. ACS APPLIED MATERIALS & INTERFACES 2024; 16:712-722. [PMID: 38157368 DOI: 10.1021/acsami.3c14823] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2024]
Abstract
Mineralization by MgO is an attractive potential strategy for direct air capture (DAC) of CO2 due to its tendency to form carbonate phases upon exposure to water and CO2. Hydration of MgO during this process is typically assumed to not be rate limiting, even at ambient temperatures. However, surface passivation by hydrated phases likely reduces the CO2 capture capacity. Here, we examine the initial hydration reactions that occur on MgO(100) surfaces to determine whether they could potentially impact CO2 uptake. We first used atomic force microscopy (AFM) to explore changes in reaction layers in water (pH = 6 and 12) and MgO-saturated solution (pH = 11) and found the reaction layers on MgO are heterogeneous and nonuniform. To determine how relative humidity (R.H.) affects reactivity, we reacted samples at room temperature in nominally dry N2 (∼11-12% R.H.) for up to 12 h, in humid (>95% R.H.) N2 for 5, 10, and 15 min, and in air at 33 and 75% R.H. for 8 days. X-ray reflectivity and electron microscopy analysis of the samples reveal that hydrated phases form rapidly upon exposure to humid air, but the growth of the hydrated reaction layer slows after its initial formation. Reaction layer thickness is strongly correlated with R.H., with denser reaction layers forming in 75% R.H. compared with 33% R.H. or nominally dry N2. The reaction layers are likely amorphous or poorly crystalline based on grazing incidence X-ray diffraction measurements. After exposure to 75% R.H. in air for 8 days, the reaction layer increases in density as compared to the sample reacted in humid N2 for 5-15 min. This may represent an initial step toward the crystallization of the reaction layer. Overall, high R.H. favors the formation of a hydrated, disordered layer on MgO. Based on our results, DAC in a location with a higher R.H. will be favorable, but growth may slow significantly from initial rates even on short timescales, presumably due to surface passivation.
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Affiliation(s)
- Jacquelyn N Bracco
- School of Earth and Environmental Sciences, Queens College, City University of New York, Queens, New York 11367-0904, United States
- Earth and Environmental Sciences, Graduate Center, City University of New York, New York, New York 10016-4309, United States
| | - Gabriela Camacho Meneses
- School of Earth and Environmental Sciences, Queens College, City University of New York, Queens, New York 11367-0904, United States
| | - Omar Colón
- School of Earth and Environmental Sciences, Queens College, City University of New York, Queens, New York 11367-0904, United States
| | - Ke Yuan
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Joanne E Stubbs
- Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, United States
| | - Peter J Eng
- Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, United States
- James Franck Institute, The University of Chicago, Chicago, Illinois 60637, United States
| | - Anna K Wanhala
- Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, United States
| | - Jeffrey D Einkauf
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Matthew G Boebinger
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Andrew G Stack
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Juliane Weber
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
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