Effect of surface oxygen groups in the electrochemical modification of multi-walled carbon nanotubes by 4-amino phenyl phosphonic acid

Electrochemical functionalization of pristine Multi-walled Carbon Nanotubes (MWCNTs) and oxidized MWCNTs by nitric acid with 4-aminophenyl phosphonic acid (4-APPA) has been studied. Electrochemical modification has been carried out by cyclic voltammetry using different upper potential limits, what results in the incorporation of N and P functionalities through oligomerization and covalent attachment. The electrochemical characterization shows that there are important differences among the functionalized materials derived from the pristine MWCNTs or the oxidized materials. For the pristine MWCNTs, well-defined redox processes are observed. Characterization by X-Ray photoelectron spectroscopy, Raman spectroscopy and electron microscopy, show that oligomerization is easier for the pristine MWCNTs and the presence of oligomer chains are clearly distinguished for the lowest oxidation potentials. However, the presence of surface oxygen groups in the oxidized MWCNTs modify the interaction of the 4-APPA with the surface promoting mainly covalent attachment.