Preparation and Characterization of Defective TiO(2). The Effect of the Reaction Environment on Titanium Vacancies Formation

Among various methods of improving visible light activity of titanium(IV) oxide, the formation of defects and vacancies (both oxygen and titanium) in the crystal structure of TiO(2) is an easy and relatively cheap alternative to improve the photocatalytic activity. In the presented work, visible light active defective TiO(2) was obtained by the hydrothermal reaction in the presence of three different oxidizing agents: HIO(3), H(2)O(2), and HNO(3). Further study on the effect of used oxidant and calcination temperature on the physicochemical and photocatalytic properties of defective TiO(2) was performed. Obtained nanostructures were characterized by X-ray diffractometry (XRD), specific surface area (BET) measurements, UV-Vis diffuse reflectance spectroscopy (DR-UV/Vis), photoluminescence spectroscopy (PL), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) spectroscopy. Degradation of phenol as a model pollutant was measured in the range of UV-Vis and Vis irradiation, demonstrating a significant increase of photocatalytic activity of defective TiO(2) samples above 420 nm, comparing to non-defected TiO(2). Correlation of EPR, UV-Vis, PL, and photodegradation results revealed that the optimum concentration of HIO(3) to achieve high photocatalytic activity was in the range of 20–50 mol%. Above that dosage, titanium vacancies amount is too high, and the obtained materials’ photoactivity was significantly decreased. Studies on the photocatalytic mechanism using defective TiO(2) have also shown that (•)O(2)(−) radical is mainly responsible for pollutant degradation.