Isophthalic acid-functionalised multiwalled carbon nanotubes as an alternative nanolayer for the layer-by-layer assembly with poly(xylylviologen)

Multiwalled carbon nanotubes (MWNTs) have been functionalised with 5-aminoisophthalic acid in an aqueous solution through an environmentally friendly diazonium-based process. The as-prepared isophthalic acid (IPA)-modified MWNT (IPA-MWNT) hybrids became more easily suspended or dissolved in water. The relative content of the covalently attached IPA substituents was about 7–9% (w/w) in the hybrids. Field emission transmission electron microscopic images revealed that the thickness of the IPA layer was about 1–2 nm. These IPA-MWNT hybrids were used as an alternative layer to construct three-dimensional thin films with a positively charged poly(p-xylylviologen) (PXV) derivative by the layer-by-layer (LBL) method. The assembling process was monitored by using UV–vis absorption spectra and cyclic voltammograms, which indicated an increase of the absorption intensity or redox current intensity after each assembly of the polyelectrolyte. X-ray photoelectronic spectra indicated that the IPA-MWNTs/PXV multilayer was composed of the elements of C(1s), N(1s), and O(1s), which were from either the functionalised IPA-MWNTs or PXV. Finally, it was revealed that the IPA-MWNT hybrids randomly arranged on the substrate surface; the film thickness increased with layer numbers of the LBL films.