Structural and bandgap properties of titanium dioxide nanotube/graphene oxide composites prepared by a facile hydrothermal method
This work investigated the optical and structural properties of hydrothermal titanium dioxide nanotube/graphene oxide (TNT/GO) composites. Transmission electron microscope (TEM) images showed the tubular titanate with a homogeneous outer diameter size 8 nm and a decrease of the TNT length in the composite sample. Besides the characteristic patterns of the tubular titanate, revealed by x-ray diffractometry, the TNT revealed both anatase (101) and rutile (110) phases. The intensity of the lowest Eg Raman active mode of anatase TiO2 increased in the composite samples and was blue-shifted from 143 cm-1 in TNT to 150 cm-1 in the composites. The blue-shift was attributed to the phonon confinement effect of TNT, hence, it is evidence of a strong interaction between TNT and GO. The optical properties were investigated by UV-vis diffuse reflectance spectra (DRS). Using the DRS data, bandgap value was determined by two methods, the first derivative and Tauc's plot. The first derivative method indicated that the TNT has two bandgap types, one from the anatase phase 3.1 eV, the other from the tubular titanate 3.5 eV. It showed that when the GO content increased, the bandgap of the anatase phase gradually disappeared, which was assigned to the crystal degradation of anatase TNT in the composite. The effect, of GO, in the composite, on the optical properties was determined and clarified.