The present disclosure relates to a carbon nanotube sponge comprising: a plurality of carbon nanotubes combined by van der Waals force to form a free-standing structure, wherein a plurality of micropores are defined by adjacent carbon nanotubes; and a plurality of carboxyl groups and hydroxyl groups located on surfaces of the plurality of carbon nanotubes; wherein a weight percentage of the carboxyl groups in the carbon nanotube sponge ranges from about 10% to about 20%, and a weight percentage of the hydroxyl groups in the carbon nanotube sponge ranges from about 5% to about 15%.