Nano-composite membranes and methods for making them are described. The nano-composite membranes a made from a layer of oriented carbon nanotubes fixed in a polymeric matrix. Methods for efficient, facile, and inexpensive fabrication of the nano-composite membranes using a filtration method are also described. The carbon nanotubes may also be modified with chemical functional groups to promote their orientation in the carbon nanotube layer or to confer to them other properties.