Eu(III)-coupled luminescent multi-walled carbon nanotubes in surfactant solutions

A carbon nanotube/inorganic hybrid material has been fabricated by coupling Eu(III) complexes onto multi-walled carbon nanotubes (MWCNTs). Successful coupling has been verified by X-ray photoelectron spectroscopy (XPS) measurement where a clear signal from Eu3d has been identified. When sonicated in hexaethylene glycol monododecyl ether (C12E6) or sodium dodecyl sulfate (SDS) aqueous solutions, the MWCNTs with Eu-complex attached (denoted as Eu-MWCNTs hereafter) can be dispersed. UV–vis measurements on a dilute dispersion of Eu-MWCNTs in SDS aqueous solution reveal the characteristic absorption from Eu(III) complexes, which gives further proof of the successful coupling. The strong luminescent properties of Eu-MWCNTs allow them to be observed directly under a fluorescence microscope. Interestingly, it is found that Eu-MWCNTs can undergo continuous movements in C12E6 or SDS dilute solutions. When Eu-MWCNTs are incorporated into the lyotropic liquid crystal phase formed by C12E6 (above 40% by weight), however, movements have been hindered. Small angle X-ray scattering measurements showed that Eu-MWCNTs are ordered in the lyotropic liquid crystal. Fluorescence microscopy observations reveal that the luminescent properties of the Eu-MWCNTs have not been affected by the liquid crystalline surfactant matrix.