The effects of the reaction parameters were systematically investigated on the amine loading during the functionalization of cellulose nanofibrils (CNFs) using N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane (APMDS). Meanwhile, the mechanical and CO2 adsorption characteristics of the CNF aerogels were examined. Tertiary butanol was highly suitable for the functionalization. The amine loading of 9.02 mmol.g(-1) was achieved with 6% APMDS. APMDS reacted with the hydroxyl groups mainly at C6 on CNFs, and the introduced primary amine groups were intact. The elastic modulus and yield stress of the aerogel from the modified CNFs were 267 and 9.75 kPa, respectively. The CO2 uptakes of the modified CNF aerogel were 1.02 and 0.35 mmol.g(-1) at 25 degrees C, respectively, at 15 kPa by chemical and physical interactions, respectively. The chemisorption dominated, but this domination decreased gradually with pressure. Therefore, the APMDS-premodified CNF aerogel was promising for the capture of low partial pressure CO2.