TiO2 Nanotubes for photocatalytic degradation of methylene blue

Abstract

Titanium dioxide remains one of the most studied semiconductor for photocatalytic applications due to its low cost production, reduced toxicity, ability to break down the organic pollutants and possibility to achieve complete mineralization. In this work, we report on results of the photocatalytic activity of titanium dioxide nanotubes fabricated by electrochemical anodization technique in an electrolyte solution containing a mixture of hydrofluoric acid, ethylene glycol and phosphoric acid. The morphology and crystallinity of the obtained nanotubes were investigated by means of electron microscopy and it was found that nanotubes have a constant outer diameter of 200 nm and an internal conical shape where the diameter gradually decreases from 120 nm at the wide end to 50 nm at the narrow end. The transmission electron microscopy investigation defined two different phases of titanium dioxide obtained after annealing of amorphous TiO2 in air at 650 °C and 850 °C. Photocatalytic activity of the samples have been evaluated in methylene blue solution in the presence of dispersed nanotubes under visible and UV irradiation by means of UV/Vis spectroscopy. Anatase phase TiO2 shows the best performance degrading 85 % of dye in 25 min under UV illumination, while rutile phase with anatase inclusions shows the best results with a 50 % decay of dye concentration in 25 min under visible light illumination.