Follow:

CO2 capture of various ST-LDO samples

https://doi.org/10.1039/D0DT01587C

“The CO2 adsorption capacity of the various ST-LDOs at 40 °C is shown in Fig. 4 and S4–S9. CO2 adsorption by LDOs is a process involving both chemisorption and physisorption. For each sample, we observe that CO2 physisorption is around twice that of chemisorption. LDO-W showed a total CO2 adsorption of 0.64 mmol g−1 (0.44 and 0.20 mmol g−1 for physisorption and chemisorption respectively). Overall, ST-LDOs show a CO2 adsorption capacity increase of ca. 50% in both physisorption and chemisorption.”

4tOyEyu9

LDO-E exhibited the highest total CO2 uptake of 1.01 mmol g−1, which represents a 58% increase compared with LDO-W. This is higher than previously reported figures for CO2 capture using LDOs under similar conditions. Sharma et al. have reported the highest to date of 0.38 mmol g−1 at 30 °C using a calcination temperature of 350 °C while Shang et al. reported a total CO2 capture value of 0.83 mmol g−1 for an acetone-treated Mg3Al CO3 LDH (pretreatment temperature of 180 °C).26,35LDO-EA exhibited a lowest CO2 uptake of 0.80 mmol g−1 amongst the ST-LDO samples tested. The chemisorption value of 0.30 mmol g−1 was comparable with the other solvent treated samples, but the physisorption figure has decreased due to the lower surface area.

It can be observed that the CO2 adsorption per g of all LDOs have a positive correlation with their surface area (Fig. S10). Simply expressed, the higher the surface area, the more active adsorption sites are exposed, leading to a higher CO2 adsorption.

All solvent treated samples, with the exception of LDO-EA, exhibited a physisorption value similar to the total adsorption value of LDO-W. There seems to be a linear correlation (R = 0.94) relating the CO2 adsorption per surface area to the ratio total acidic to basic sites (mmol g−1) of the LDOs (Fig. 5). This atomic-level origin of this linear relationship to not clear at this time. However, it is worth noting that the acid sites as measured heavily involve the surface hydroxyl groups as shown in Scheme S1. These hydroxyl groups can participate in CO2 adsorption via weak CO2 bidentate bonding. But this bonding mode is not present in the CO2 TPD due to the adsorption temperature of 100 °C.31,34 This observation suggests that solvent treatment not only disperses individual nanosheets increasing the accessible surface area but also the solvent interacts with the surface and selectively blocks acidic sites, leading to a slightly less active surface for CO2 adsorption.”

5ASPZMVb

Leave a Comment