We report the synthesis and Fourier Transform Infrared spectroscopy characterization results dealing with the surface modification of silica aerogels obtained via a two-step sol–gel process where various silicon precursors and co-precursors were used. The hydrolysis and poly-condensation steps were followed by carbon dioxide supercritical drying ( T c = 31.1 °C; P c = 73.7 bar). The silicon precursors contain four identical hydrolysable alkoxy groups (methoxy or ethoxy), while in the co-precursors, one of the alkoxy groups is substituted by a non-hydrolysable alkyl group (methyl, ethyl, n-propyl, iso-butyl, n-octyl, vinyl or phenyl). Identically, surface-functionalized silica aerogels were obtained from various silicon precursor/co-precursor combinations and their chemical structures were compared. The infrared spectroscopy revealed the existence of chemically comparable solid networks with some differences due to the nature of the silicon precursors.