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The present study investigated the role of structural parameters such as pore size, pore volume, and specific surface area of mesoporous silica on the CO2 sorption performance of various amine-functionalized adsorbents. A series of mesoporous silica with different structural properties KIT-6, MCM-41, SBA-15, and HV MCM-41 were synthesized and functionalized with pentaethylenehexamine (PEHA) by wet impregnation. The CO2 sorption performances of the sorbents were evaluated using high pressure gas adsorption analyzer. The sorption capacity of adsorbents follows the order: MCM-41 < HV MCM-41 < SBA-15 ≈ KIT-6 at 105 °C and 1 bar. Larger pore size reduces the mass transfer resistance, and large pore volume improves the PEHA distribution inside the pores. The high specific surface area has little impact during adsorption. Due to the 3D structure with interconnected pores, KIT-6 shows the lowest heat of regeneration (57.8 kJ/mol CO2) during adsorption. The PEHA-impregnated KIT-6 (K-60 PEHA) shows the highest sorption capacity 4.48 mol CO2/g at 105 °C and 1 bar. It also exhibit fairly stable sorption performance up to 10 adsorption/desorption cycles between in the temperature range of 90–105 °C.

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The present study targeted the synthesis of CO2 adsorbent by impregnation of DETA, TEPA, PEHA, and polyethylenimine in KIT-6 with a confiscated structure directing agent in minimum time and energy. The adsorbents were characterized and revealed the influence of polyethylenimine with CO2 at a wide range of temperatures. An examination by TGA confirmed that PluronicP123 present in adsorbent enhances its thermal stability and acts as a carrier for CO2 to the inner layer of polyethylenimine during adsorption. CO2 sorption capacity of the adsorbent was found to be dependent on the polyethylenimine loading, temperature, pressure, and the surfactant PluronicP123. At higher temperatures, adsorbents showed a positive impact for CO2 adsorption; however, a negative effect was exhibited in amine efficiency. The sorption capacity decreased with increasing the molecular weight of polyethylenimine following the order PEI-25K (66 mg CO2/g) < PEI-800 (114 mg CO2/g) < TEPA (124 mg CO2/g) < PEHA (139 mg CO2/g) at 75 °C. However, 60 wt % PEHA impregnated KIT-6 showed the stable sorption capacity of 170–184 mg CO2/g at 90–105 °C and 1 bar.