Influence of adsorption time and pressure using cross linked polymers

https://doi.org/10.1039/D1MA01072G

“The gas sorption isotherm of 10 : 1 (R) from 0.01–1 bar at 30 °C was compared to those of 10 : 1 (V) and 25 : 1 (V), Fig. 11(a). The interpolated CO₂ uptake of 10 : 1 (R) is 1.06 mmol g⁻¹ at 0.1 bar and 2.01 mmol g⁻¹ at 1 bar (Table S5, ESI†). Although slightly lower than the uptake at 0.1 bar for 10 : 1 (V), 10 : 1 (R) does also show higher low-pressure uptake than 25 : 1 (V). This is likely due to the greater access to the amine binding sites via the space between the spherical particles. To confirm this, the surface area of 10 : 1 (R) was measured by using the BET method. The N₂ adsorption isotherm of 10 : 1 (R), shown in Fig. S12 (ESI†), is similar to that of 10 : 1 (V), indicating a non-porous material. The surface area, calculated as 11.827 m² g⁻¹ was even lower than for the other adsorbents, which showed no clear trend (Table S1, ESI†). The surface areas do not corroborate the differences observed in the materials’ microstructures, in that those composed of smaller, more discrete spherical particles would have a significantly higher surface area to those whose morphologies are of a more dense and continuous network. Gaining accurate surface area measurements for these materials is challenging. Firstly, they have very low surface areas. Secondly, the N₂ adsorption data are not necessary equilibrium isotherms; the affinity for these materials to N₂ is very low, and further, at 77 K, the polymers are likely in a glassy state, lacking flexibility. It is probable that it is this flexibility that, at ambient temperatures, affords the formation of small voids receptive to the inclusion of the CO₂ molecule, with a smaller kinetic diameter than N₂, enabling access to amines with which CO₂ chemisorbs. Such a phenomenon has been suggested in previous work in which positron annihilation spectroscopy was carried out on a cross-linked CO₂ sorbent.⁶⁰”

“Fig. 11 (a) Single-component CO₂ sorption isotherms of 10 : 1 (V), 25 : 1 (V) and 10 : 1 (R) (in green) at 30 °C from 0.1–1 bar. (b) Single-component CO₂ sorption isotherms of 10 : 1 (R) at 30 °C, 45 °C and 60 °C from 0.1–1 bar.”