Effect of Granulometric and Phase Transformations on the Photocatalytic Properties of Annealed Magnetron Titanium Dioxide Films

The purpose of the study is to reveal regularities between granulometric and phase transformations occurring during the thermal treatment of magnetron titanium dioxide films and their photocatalytic properties. 

Methods. The samples were synthesized using the magnetron sputtering device MVU TM "Magna T" (Russia) and the heater Mini Lamp Annealer MILA-5050. Morphological features and changes in the film surface structure after annealing were studied using a JEOL JSM-6610LV scanning electron microscope (SEM) (SEM, 20 kV, up to 100000×, X-Max Silicon Drift Detector, Oxford Instruments). The samples were characterized by small-angle X-ray scattering in the linear collimation mode (diffractometer SAXSess mc2, Anton Paar, Austria). The SEM images were processed using the program Digimizer. The photocatalytic activity of titanium dioxide films was studied by the spectrophotometric method during the oxidation reaction of the organic dye methylene blue.

Results. As a result of the study, it was found that with increasing time and temperature of thermal treatment, the dispersion and average grain size increase. In samples obtained at a temperature of 800 °C, a significant coarsening of the grain structure is observed with a simultaneous increase in the crystallinity of the samples. Thermal annealing leads to phase transformations in TiO₂ nanofilms. At a temperature of 400°C, an anatase phase is formed, which, upon annealing at 600°C and 800°C, irreversibly transforms into the rutile phase. 

Conclusion. The TiO₂ grain size and phase composition determine the physicochemical properties of annealed magnetron titanium dioxide films. Thermal annealing leads to changes in particle size distribution and phase transformations in the samples. The formation of nanofilms with a phase composition (Anatase/Rutile 70%/15%) with a low degree of crystallinity makes it possible to obtain nanofilms with the highest photocatalytic activity. An increase in the annealing temperature up 800°C leads to an increase in the crystallinity of the nanofilm and the transformation of the anatase phase into rutile, which reduces the photocatalytic activity of titanium dioxide nanofilms. 

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