Mesoporous Silica-Polyethyleneimine Composites as High-Capacity Adsorbents for CO2 Adsorption: Isotherm and Thermodynamic Analysis

Abstract

In this study, polyethyleneimine-mesoporous silica composite materials were prepared and the effectiveness of the promising sorbents in adsorbing CO2 was evaluated, along with the impacts of the silica support types (Mesoporous Silica Nanoparticles (MSN) and Mobil Composition of Matter No.48 (MCM-48)), polyethyleneimine (PEI) loading percentages (50 and 70 wt.%), calcination, surface functionalization by alkyl chains (CTMABr), and adsorption temperature (75 and 100 degrees C). The analysis's results revealed that the pores of the sorbents were mostly covered with PEI molecules following PEI-functionalization, and the specific surface area and pore volume were also reduced with rising amine content. The highest CO2 adsorption capacities were achieved for UC-MCM-48-50 and UC-MSN-50 at 2.26 mmol/g and 3.31 mmol/g, respectively. The CO2 uptake capacities of CC-MSN-50 and CC-MCM-48-50, composed by dispersing CTMABr surfactant with the calcined materials before incorporating PEI, were remarkably similar to those of non-surfactant functionalized adsorbents. When the temperature's influence on CO2 adsorption capacity was evaluated, the maximum holding capability adsorbent UC-MSN-50 had a slight increase in adsorption capacity (similar to 3.6%), whereas UC-MCM-48-50 had a considerable drop (similar to 23.9%) as the temperature elevated to 100 degrees C. Besides, Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin isotherms were used to model pure CO2 adsorption data, and a thermodynamic study was applied. In conclusion, a low-cost and more beneficial approach, which included less PEI handling and eliminating the calcination step, was implemented to enhance the CO2 sorption capacity of composites of PEI with the long alkyl chain template MCM-48 or MSN silica support materials.