Facile functionalization of multi walled carbon nanotubes with L-Proline: A spectroscopic approach

Abstract

Oxidized multiwalled carbon nanotubes were functionalized with proline using a simple ultrasonic blending process. This work is a preliminary studies of analyzing the functionalization of L-Proline (L-Pro) with MWCNTs . The chemical attachment of L-Pro on CNTs is of significant interest, since it not only improve the nanotube solubility but also opens a broad prospect for their biomedical applications. The interaction between the CNTs and amino acid is very important for understanding the interaction mechanism between CNTs and biomolecules. The various properties of the functionalized samples were evaluated by the spectroscopic characterization techniques like X-ray diffraction, UV–Vis, Scanning electron microscopy, Transmission electron microscope, Fourier transform infrared and Raman analysis. The observed sharp peaks attributes to the higher degree of crystalline nature. The shift in the XRD pattern indicates that the attachment of L-Pro on the surface of oxidized MWCNTs. The appearance of new peaks are due to the presence of the L-Pro on the MWCNTs, which confirms the attachment of the Pro on the surface of the MWCNTs. The UV–Vis spectra shows the shift in the lower cut off wavelength of the L-Pro functionalized MWCNTs, which confirms the successful attachment of the L-Pro on the surface of the MWCNTs. From the UV analysis, the new broad characteristic peaks appeared at 381 nm, 387 nm, 388 nm of L-Pro functionalized MWCNTs can be attributed to the charge transfer complex available on the MWCNTs. The L-Proline functionalized MWCNTs shows a high surface roughness, which is due to the partial damage of the graphitic carbon during functionalization. The presence of C–N stretching vibrations confirm the successful functionalization. The higher intensity ratio reveals that the greater extent of C=C rupture, which indicates the higher covalent functionalization on the surfaces of the MWCNTs. The enhancement of the ID/IG ratio of L-Pro functionalized MWCNTs are due to the amidation, which is the carboxylic acid group of oxidized MWCNTs reacts with the amino groups of Proline and due to the results of the radical reaction with MWCNTs. The g-values from EPR analysis confirms that the system remains isotropic which is due to the finite unpaired electron density. Hence, the successful functionalization of MWCNTs with L-Proline is confirmed, which is highly useful for further chemistry with other biomolecules like peptides, proteins and also leads to the research for the treatment of neuro degenerative diseases.