a molecular species is covalently attached to elemental carbon by exposing the carbon to a reaction mixture containing a strong base and a compound of the formula or in which x denotes a covalently attached atom or group capable of forming an x − anion and each z is a moiety comprising a plurality of atoms , but which does not have a hydrogen atom directly attached to the atom which itself is directly attached to the — ch 2 x or — chx group . the carbon substrate may be graphite or carbon nanotubes .