CO2 capture using hierarchically ordered porous silica with different amine modifications

https://doi.org/10.3390/inorganics10070087

“Figure 7 displays the CO₂ adsorption isotherms of HSMs(DC)-0.15-APTES, HSMs(DC)-0.15-NTPEA, and HSMs(DC)-0.15-NH₂ modified with amine groups. The amounts of adsorbed CO₂ were 1.98 mmol/g for HSMs(DC)-0.15-APTES, 2.22 mmol/g for HSMs(DC)-0.15-NTPEA, and 1.38 mmol/g for HSMs(DC)-0.15-NH₂ at 273 K and 1 bar. It was found that the CO₂ adsorption capacity of HSMs(DC)-0.15 improved after modification with APTES and NTPEA through the post-grafting method. The surface area and pore volume of HSMs(DC)-0.15-APTES were higher than those of HSMs(DC)-0.15-NTPEA, while the amount of CO₂ adsorption HSMs-0.15-NTPEA was higher than that of HSMs(DC)-0.15-APTES. On the basis of the corresponding surface area and weight loss data, the obtained -NH_x densities were 1.41 × 10⁻³ mmol/m² for HSMs(DC)-0.15-APTES and 3.7 × 10⁻³ mmol/m² for HSMs-0.15-NTPEA. Compared with HSMs(DC)-0.15-APTES, HSMs(DC)-0.15-NTPEA, with its higher -NH_x density, had a higher amount of CO₂ adsorption [48]. These results suggest that the key parameters of the CO₂ adsorption capability of amine-modified materials are not only surface area and pore volume but also the density of -NH_x on the surface of the matrix. Meanwhile, as shown in Figure 7, the capacity of CO₂ adsorption for HSMs(DC)-0.15-NH₂ declined to 1.38 mmol/g, which was lower than that of unmodified HSMs(DC)-0.15. As evidenced by N₂ adsorption–desorption measurement, the main reason was that the pore was filled by APTES molecules; therefore, a certain number of pores was blocked and inaccessible to CO₂ molecules, resulting in a low CO₂ sorption capacity.”

“Figure 7. CO₂ adsorption isotherms of samples after amine modification at 273 K.”