Hydrogen titanate nanotubes doped with graphene oxide for the photocatalytic degradation of methylene blue

Abstract Hydrogen titanate nanotubes (NT) modified with small amounts of graphene oxide (GO, 1, 2 wt%) were prepared by alkali hydrothermal synthesis. For comparison purposes, commercial titania Degussa P25 was used. The synthesized NT and GO-modified NT materials were characterized by N 2 physisorption, UV–Vis diffuse reflectance spectroscopy, powder X–ray diffraction (XRD), scanning electron microscopy with X–ray energy dispersive spectroscopy (SEM–EDS), transmission electron microscopy and Raman spectroscopy. XRD revealed that the hydrogen trititanate crystalline phase was present in all the synthesized materials with and without GO. The band gap energy of the NT materials modified with GO was slightly higher (3.22–3.28 eV) than for the unmodified NT (3.10 eV) due to a better separation of individual titanate nanotubes by GO, acting as a spacer. The obtained materials were evaluated as photocatalysts for the degradation of methylene blue (MB) dye under UV irradiation for 2 h. Previously, the adsorption–desorption equilibrium of MB dye on the catalysts was achieved. The addition of GO to titanate nanotubes increased their textural properties and MB adsorption capacity up to 98.1 mg/g cat for the NT catalyst with 2 wt% of GO. In addition, the above catalyst showed lower final concentration of MB compared to the TiO 2 Degussa P25 reference, reaching near 95% of MB decomposition at 2 h under UV irradiation. The improved photocatalytic efficiency of the NTGO composites was attributed to a combined adsorption-degradation mechanism of MB dye, where both NT and GO participate in MB adsorption and GO helps to avoid recombination of photogenerated electron–hole pairs. Effects of the amount of the catalyst, MB concentration and solution pH were also evaluated.