Cellulose nanofibers (CNFs) aerogels with controllable surface wettability were prepared by grafting poly( N, N-dimethylamino-2-ethyl methacrylate) (PDMAEMA) polymer brushes via surface-initiated atom-transfer radical polymerization. After grafting PDMAEMA polymer, the surface of the aerogel was hydrophobic. However, in the presence of CO2, the surface of the aerogel gradually changes from hydrophobic to hydrophilic. The porous structure and CO2-responsiveness of PDMAEMA brushes within the CNFs aerogels allowed for the on-off switching of the oil-water mixture separation process. These CNFs aerogels were recyclable and displayed attractive separation efficiency for oil-water mixture and surfactant-stabilized emulsions. Furthermore, the switchable surface wettability holds an advantage of avoiding oil-fouling, which will greatly improve its recyclability.