Effect of different coupling agents in the doping of graphite oxide with 3–3′ diaminobenzidine: textural, structural and electrical properties

Abstract

The doping reactions of graphite oxide (GO) with 3-3′-diaminobenzidine (DAB) were studied using N, N′-dicyclohexylcarbodiimide (DCC), cyanuric chloride (CC) and hexafluorophosphate (HATU) as coupling agents. The bifunctionality of the coupling agents aid to interact GO functional groups with amino groups of DAB without being part of the final product. The doped materials (d-GO) and GO were characterized by thermogravimetric analysis, x-ray diffraction, FTIR/Raman spectroscopy, x-ray photoelectron, high-resolution electron microscopy and cyclic voltammetry. The GO-HATU material was more thermally stable than other graphitic material, with at 10% weight loss at 300 °C, this thermal stability is related to a more difficult intramolecular physisorbed water removal process than the other d-GO materials. GO-CC and GO-HATU materials presented 8.2 and 8.0 Å of interlayer spacing, which was associated with a good oxidation-doping process. Besides, these two materials showed modifications in the vibrations by FTIR technique, corresponding to epoxy and hydroxyl groups of the GO being more susceptible to react with the amino groups. Moreover, I _D /I _G ratio calculated by Raman Spectroscopy presents the following trend 0.70, 0.94, 0.97 and 1.04 for GO, GO-CC, GO-DCC and GO-HATU, respectively, this increase is related with a major disorder during the doping process. XPS analysis shows C–N and N=C bands for high resolution of C 1s and N 1s, respectively, for d-GO materials. This possibly suggests the formation of benzimidazoles during the oxidation-doping process, this generates a similar -non-lattice and -lattice oxygen amount for O 1s related to crosslinking between the functional groups of GO and DAB which improve the electronic mobility between the surface and the bulk of the final graphitic material. Finally, the obtained d-GO materials were investigated as a working electrode for electrochemical capacitors and all of them showed typical capacitive behaviour.