Methods and compositions to extract radionuclides such as various actinides and lanthanides from organic and/or aqueous solutions by utilizing extractant functionalized carbon nanotubes are disclosed. More particularly, phosphorous-containing (such as phosphine oxides, phosphoric acids or phosphates) organic extractants and other predesigned extractants (such as crown ethers, calncrown derivatives, malonamide and diglycolamide derivatives, polyethylene glycol derivatives, cobalt dicarbollide derivatives, and N-donating heterocyclic ligands) can be covalently and/or non-covalently employed on the surfaces and/or ends (tips) of carbon nanotubes for the purpose of removal radionuclides such as various actinides and lanthanides from organic and/or aqueous solutions. Extractant functionalized carbon nanotubes can be used for extracting radioactive nuclides from nuclear waste or spent nuclear fuel, which are produced and/or reprocessed from the nuclear power generation or other nuclear application.