Nanostructured titanium dioxide-based photocatalysts for self-cleaning concrete: assessment of effects of phase composition on photocatalytic activity of TiO2

Introduction. Currently, the development of photocatalytically active cement-based materials with self-cleaning properties is a promising area of building materials science. Self-cleaning concrete is obtained by using photocatalytic additives, of which titanium dioxide (TiO2) is the most common. It has been found that the functional properties of TiO2 depend largely on its phase composition. This study aimed to establish the patterns of influence of phase composition on the photocatalytic activity of titanium dioxide under the impact of artificial ultraviolet and natural solar radiation and to identify the most effective titanium oxide-based photocatalysts for subsequent use in the composition of self-cleaning concrete. Methods and materials. Four titanium dioxide samples, namely two industrial samples and two samples synthesized by hydrolysis of titanium alkoxide in acidified water-alcoholic medium followed by calcination at 500 °C, were the objects of the study. X-ray powder diffractometry was the method used to investigate the structure parameters of TiO2 samples. The model reaction of oxidative degradation of methylene blue under UV- and daylight exposure was the means for studying the photocatalytic activity of titanium dioxide samples. Results and discussion. It was found that polymorphic modifications of titanium dioxide had a multidirectional effect on its functional characteristics, in particular, a rise in the content of anatase and rutile led to an increase and decrease in the photoactivity of TiO2 samples, respectively. The single-phase sample with anatase structure was most effective under UV irradiation, while the three-phase sample with the anatase : brookite : rutile ratio of 67% : 13% : 20% had the highest activity under daylight exposure. The photocatalyst composition, including several polymorphs of TiO2 with a predominance of anatase form (more than 50%), allowed to achieve a synergistic effect of increasing the photocatalytic activity of titanium dioxide under conditions of solar radiation due to the formation of type-II semiconductor heterojunctions. Heterostructures made it possible to improve the spatial separation of charge carriers and to reduce the recombination rate of photogenerated electron-hole pairs. Conclusion. The obtained results indicated the possibility of improving the functional characteristics of titanium oxide-based additives for self-cleaning concrete due to the targeted regulation of their phase composition by optimizing the synthesis parameters of photocatalytic modifiers.