Tuning the photoelectronic and photocatalytic properties of single-crystalline TiO2 nanosheet array films with dominant {001} facets by controlling the hydrochloric acid concentration

Single-crystalline TiO2 nanosheet array films with tunable percentage of exposed {001} facets were synthesized on FTO by a simple hydrothermal method. The effects of the hydrochloric acid concentration on morphology, crystal structure, and optical property have been investigated by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, micro-Raman spectroscope system, and UV–Vis spectrophotometer. When the hydrochloric acid concentration increases from 4.8 to 5.2 mol/L, dense regular nanosheets tend to grow perpendicular to the substrate surface, and the percentage of exposed {001} facets is increasing from 76 to 84 %. Evolution of these nanosheet array films has accompanied by significant variations of photoelectronic and photocatalytic properties. The intensity of Raman peak E g at 144 cm−1 decreases, and the photocurrent increases when more proportion areas of {001} facets are exposed. The sample prepared at hydrochloric acid concentration of 4.8 mol/L shows the highest photocatalytic activity. This can be explained by the preferential carrier transport to different facets of the TiO2 crystal with tradeoff relation between the {101} and {001} facets, and a increasing of total catalytic sites.