Location of MgCO3 growth during NaNO3–MgO carbon capture

https://doi.org/10.1039/D2TA02897B

“We gained further insight into the morphology and location of formation of MgCO₃ that is formed during carbonation by SEM (Fig. 5 and S6–S8†). Prior to the morphological analysis, the sample was rinsed in water for 1 minute to remove NaNO₃ exposing the MgCO₃ grown at the bottom of the grooves (NaNO₃–MgO_B_xhours-CO2 where the subscript x refer to carbonation time).^9,15 Representative examples of MgCO₃ particles grown after 0.5, 1, 2, and 5 hours of carbonation (groove with a depth of d_groove = 44 μm) are shown in Fig. 5a–d. Additionally, an overview of the MgCO₃ particles grown after 5 hours at the bottom of deep and shallow grooves are shown in Fig. S6–S7.†”

“Fig. 5 Growth of MgCO₃ crystals with time when exposed to CO₂ at 330 °C (sample NaNO₃–MgO_B_xhours-CO2 where the subscript x corresponds to the carbonation time ranging between 0.5 hour and 5 hours). Prior to imaging/analysis the samples are rinsed in H₂O to remove NaNO₃. (a–d) SEM images taken at the bottom of the MgO groove (groove depth 44 μm) after, respectively, 0.5 hour, 1 hour, 2 hours and 5 hours of exposure to CO₂. (e) Mean particle size of MgCO₃ formed on the bottom of the grooves of depth 155 μm as a function of carbonation time (error bars show the standard deviation of the measured particle diameter based on more than 100 particles per data point). (f) Exemplary particle size distribution in the groove of depth 155 μm after 5 hours of carbonation (normal distribution function was used for fitting).”

“The mean particle size of MgCO₃ as a function of carbonation time (groove depth 44 μm, NaNO₃–MgO_B_xhours-CO2, x = 0.5, 1, 2, 5 hours) is plotted in Fig. 5e and the particle size distribution after 5 hours of carbonation at 330 °C in CO₂ is given in Fig. 5f (groove depth 44 μm, NaNO₃–MgO_B_5hours-CO2). The number of particles (MgCO₃ particles as those observed in Fig. 5a–d are counted as one particle) is plotted as a function of groove depth (at the flat bottom) and carbonation time in Fig. S8.† Notice, only particles located at the flat bottom of the grooves in MgO_B are counted and since the bottom area is smaller in deeper grooves, the number of particles is normalized by the area of the bottom of the grooves. The CO₂ capture performance of AMS-promoted MgO powder samples can be quantified for example by its weight change in a TGA experiment, however, the weight changes (per gram of sample) in the model system are too small to be detected. To quantify the amount of absorbed CO₂, instead we determined the fraction of the MgO surface (at the bottom of the groove) that is covered by MgCO₃ in Fig. S7† and the volume of MgCO₃ formed by profilometry below.”

“Figure S6. SEM image of grooves 3-4 (top to bottom) after 5 hours of carbonation at 330°C, i.e. NaNO3-
MgO_B5 hours-CO2. NaNO3 has been removed by a rinse in water and the sample was coated with PtPD
prior to SEM (secondary electron) imaging”

“Figure S7. SEM image of grooves 7-9 (top to bottom) after 5 hours of exposure to CO2 at 330°C, i.e.
NaNO3-MgO_B5 hours-CO2. MgCO3 particles grow close and far away from the TPB (top of groove).
NaNO3 has been removed by a rinse in water and the sample was coated by PtPd prior to SEM (secondary
electron) imaging.”

“Figure S8. Number of MgCO3 of particles per unit area at the bottom of the MgO grooves in MgO_B
determined from SEM images using ImageJ. a) Number of MgCO3 particles as a function of groove depth
and b) number of MgCO3 particles as function of carbonation time for the nine grooves studied (groove
depth given in µm). The black data points correspond to the mean number of particles per unit area for a
given groove depth (a) or a given carbonation time (b). ”

https://doi.org/10.1039/D2TA02897B