Synthesis, Characterization and Gas Adsorption of Unfunctionalized and TEPA-Functionalized MSU-2

Michigan State University-2 (MSU-2) is notable potential adsorbent for carbon dioxide (CO2) due to its intrinsic properties, which include its highly interconnected three-dimensional (3D) wormhole-like framework structure, high specific surface area, and its large total pore volume, as well as its large amount of surface silanol hydroxyl groups, which facilitate the amine functionalization process. In this study, unfunctionalized MSU-2 was synthesized via a fluoride-assisted two-step process via the solution precipitation method, using Triton X-100 as the surfactant and tetraethylorthosilicate (TEOS) as the silica precursor. Then, the synthesized MSU-2 was functionalized using varying tetraethylenepentamine (TEPA) loadings of 20–60 wt%. The effect of different TEPA loadings on the properties and CO2 adsorption capacity of the MSU samples was investigated. Studies of the CO2 adsorption of the unfunctionalized and TEPA-functionalized MSU-2 samples was conducted at 40 °C and 1 bar of pressure. Furthermore, scanning electron microscopy (SEM); surface area and porosity (SAP) analysis; carbon, hydrogen, nitrogen, and sulfur (CHNS) analysis, X-ray diffractometry (XRD); Fourier transform infrared (FTIR) spectrometry; and thermogravimetric analysis (TGA) were utilized to characterize the resultant unfunctionalized and TEPA-functionalized MSU-2 with different TEPA loadings in order to study their morphologies, pore characteristics, elemental compositions, crystallographic structures, functional groups, chemical bonding, and thermal stability, respectively. The comprehensive results obtained from the analytical instruments and the CO2 adsorption studies indicated that the TEPA-functionalized MSU-2 with 40 wt% of TEPA loading achieved the highest average CO2 adsorption capacity of 3.38 mmol-CO2/g-adsorbent.