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

Abstract

Electrochemical functionalization of pristine Multiwall Carbon Nanotube (MWCNT) and oxidized MWCNT 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 polymerization and covalent attachment. The electrochemical characterization shows that there are important differences among the functionalized materials derived from the pristine MWCNT or the oxidized materials. For the pristine MWCNT, 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 MWCNT and the presence of polymer chains are clearly distinguished for the lowest oxidation potentials. However, the presence of surface oxygen groups in the oxidized MWCNT modify the interaction of the 4-APPA with the surface promoting mainly covalent attachment.

On the mechanism of electrochemical functionalization of carbon nanotubes with different structures with aminophenylphosphonic acid isomers: an experimental and computational approach

“…The N1s core-level spectra were fitted with two main contributions related to distinct nitrogen species. The first peak observed at lower binding energies, at around 400.0 eV, can be assigned to neutral amine species (–NH–) 34 and commonly found in PANI-like structures. 79,80 Additionally, this peak can also have some contribution from amide groups (–C(O)NH–) formed from condensation reactions between amino groups of monomers and oxygen groups in CNTs, thus producing covalent grafting.…”

“…57,58 An additional band of lower intensity can be clearly observed at around 1130 cm −1 after modifying the a-SWCNTs with both APPA monomers (Fig. 6A and B), which could be ascribed to asymmetric C–N–C stretching mode in quinoid structures, 34 C–H aromatic in-plane bending mode, 84,87 and to P–O–C out-of-plane stretching in an aromatic system. 34,88 Therefore, the lack of this band in modified hCNTs confirms the non-favorable effect of this carbon structure for the oligomerization process.…”

“…6A and B), which could be ascribed to asymmetric C-N-C stretching mode in quinoid structures, 34 C-H aromatic in-plane bending mode, 84,87 and to P-O-C out-of-plane stretching in an aromatic system. 34,88 Therefore, the lack of this band in modied hCNTs conrms the non-favorable effect of this carbon structure for the oligomerization process. In this case, the inset images shown in Fig.…”

“…and in the presence of CNTs. 27,[32][33][34] Additionally, the incorporation of heteroatoms into CNTs has also been studied by using other chemical methods. 35 Nonetheless, the mechanism of functionalization has not been explored in detail from fundamental and theoretical points of view so far.…”

“…[36][37][38] Therefore, a systematic study of such an effect would be convenient in many cases. In addition, many of the previous studies have focused on the electrochemical functionalization of both single-walled carbon nanotubes (SWCNTs) 32 and multiwalled carbon nanotubes (MWCNTs), 27,33,34 but without further purication treatments. However, it has been demonstrated that the presence of trace metal residues from their synthesis or modication methods could lead to misleading results in specic applications.…”