Physicochemical properties and redox behaviour of Fe-doped hybrid nanotubes of the imogolite type and their rGO nanocomposites

By ionic exchange of preformed methylimogolite nanotubes (chemical formula (OH)3Al2O3SiCH3), nanotubes with the chemical formula (OH)3Al2-xFexO3SiCH3 were obtained, with x values of 0.05 and 0.1, corresponding to a nominal Fe content of 1.4 and 2.8 wt%, respectively. The nanotubes were characterized using low angles X-ray powder diffraction; N2 sorption at −196 °C; Diffuse Reflectance UV–Vis spectroscopy and High-Resolution Transmission Electron Microscopy coupled to Energy Dispersive X-Ray Analysis. Their electrochemical behaviour was investigated by Cyclic Voltammetry: a redox behaviour was observed only with a Fe content of 2.8 wt%, likely due to Fe-oxyhydroxide clusters (FeOOH) at the nanotubes' outer surface. Based on the electrochemical and physicochemical characterizations, nanocomposites of Fe-doped methylimogolite and reduced Graphene Oxide (rGO) were obtained for the first time through a simple method, previously developed by some of us to disperse electrochemically active nanomaterials onto carbon supports. In the micro/mesoporous nanocomposites (specific surface area in the 370–284 m2 g−1 range) the NTs were highly dispersed within the 3D rGO matrix. Cyclic Voltammetry showed that the capacitive behaviour of the Fe-doped NTs alone were enhanced when they were embedded in the 3D rGO matrix.