The modified poly(ethyleneimine) (PEI) SBA-15 sorbents were prepared by impregnating a solution of n-x-PEI in methanol into SBA-15, where "x" denotes the functional group such as methyl (M), propyl (P) and 2hydroxypropyl (HP) and "n" denotes the molar ratio of the functional reagent (e.g., 1,2-epoxypropane) to total moles of nitrogen in PEI. For example, 0.25HP-PEI was prepared with methanol, PEI, and 1,2-epoxypropane solution that contained 0.25 moles of 1,2-epoxypropane per mole of nitrogen in PEI. Complete details of the synthesis and characterization of the sorbents are provided in section S7 of the SI. As expected, increasing the loading of modified PEI in the sample reduces the pore volume (Table ). Excessive PEI loading can lead to reduced CO2 uptake; several studies have previously concluded that there is a maximum adsorption capacity of PEI at around 40% organic loading in the SBA-15 framework. Thus, all studies in this work were performed at a fixed 40 wt.% organic loading in the SBA-15.