Efficient Covalent Modification of Multiwalled Carbon Nanotubes with Diazotized Dyes in Water at Room Temperature

Abstract

Tetrafluoroborate salts of diazotized Azure A (AA-N), Neutral Red (NR-N) and Congo Red (CR-N) dyes were prepared and reacted with multiwalled carbon nanotubes (MWCNTs) at room temperature, in water without any reducing agent. The as-modified MWCNTs were examined by IRATR, Raman spectroscopy, XPS, TGA, TEM, and cyclic voltammetry. The diazonium band located at ∼2350 cm in the diazotized dye IR spectra vanished after attachment to the nanotubes whereas the Raman D/G peak ratio slightly increased after dye covalent attachment at a high initial diazonium/CNT mass ratio. XPS measurements show the loss of F 1s from the BF anion together with a clear change in the high-resolution C 1s region from the modified nanotubes. Thermogravimetric analyses proved substantial mass loadings of the organic grafts leveling off at 40.5, 34.3, and 50.7 wt % for AA, NR, and CR, respectively. High-resolution TEM pictures confirmed the presence of 1.5-7-nm-thick continuous amorphous layers on the nanotubes assigned to the aryl layers from the dyes. Cyclic voltammetry studies in acetonitrile (ACN) confirmed the grafting of the dyes; the latter retain their electrochemical behavior in the grafted state. The experimental results correlate remarkably well with quantum chemical calculations that indicate high binding energies between the dyes and the CNTs accounting for true covalent bonding (140-185 kJ/mol with the CNT-aryl distance <1.6 nm), though attachment by π stacking also contributes to obtaining stable hybrids. Finally, the pH-responsive character of the robust hybrids was demonstrated by a higher degree of protonation of Neutral Red-grafted CNTs at pH 2 compared to that of the neutral aqueous medium. This work demonstrates that diazotized dyes can be employed for the surface modification of MWCNTs in a very simple and efficient manner in water and at room temperature. The hybrids could be employed for many purposes such as optically pH-responsive materials, biosensors, and optothermal composite actuators to name a few.

Polypyrrole-Wrapped Carbon Nanotube Composite Films Coated on Diazonium-Modified Flexible ITO Sheets for the Electroanalysis of Heavy Metal Ions

“…The interface between CNTs and NH 2 -ITO has been imaged by SEM ( Figure 5). The attachment of CNTs on the NH 2 -ITO surface can be noted (Figure 5a,b), thus proving the interaction of the carbon nanotubes and diazonium-modified ITO [44,45]. The SEM morphology for the interface between PPy and CNT/NH 2 -ITO ( Figure 5c) shows that PPy is wrapped around the CNTs [40], therefore confirming the structures displayed in Figure 4.…”

Polypyrrole-Wrapped Carbon Nanotube Composite Films Coated on Diazonium-Modified Flexible ITO Sheets for the Electroanalysis of Heavy Metal Ions

“…The interface between CNTs and NH2-ITO has been study by SEM ( Figure 5). The attachment of CNTs on the NH2-ITO surface can be noted, thus proving the interaction of the carbon nanotubes and diazonium-modified ITO [42,43]. The SEM morphology for the interface betwenPPy and CNT/NH2-ITO ( Figure 5b) shows that the PPy wraps around the CNTs [38] therefore confirming the structures displayed in…”

Diazonium Electrografting vs. Physical Adsorption of Azure A at Carbon Nanotubes for Mediated Glucose Oxidation with FAD‐GDH

“…Mechanistic aspects of the reaction of the aryl radicals at carbon nanotubes have been studied [26,27] . Azure A is a convenient choice for diazonium grafting due to its single pendant arylamine group.…”