Ultrasonic Spray Preparation Of TiO₂-based Porous Microspheres And Their Photocatalytic Properties

TiO₂materials have excellent properties in structural,optical and chemical properties.Recently, TiO₂materials have been a hot research topic in photocatalytic materials. The porousTiO₂microspheres with sub-micron size has been widely applied in the field of photochemicalsolar energy conversion and the use of solar energy. The size of TiO₂porous microspheres isnear ultraviolet and visible wavelength. Thus, the microspheres may display interesting lighttrapping via multiple scattering at air-solid interface and the absorption of sunlight can beimproved. Ultrasonic spray pyrolysis method is a low cost and simple process. We preparedTiO₂-based porous microspheres by this method and investigated how to enhance thephotocatalytic activity of TiO₂by Nb doping and WO3compositing. In addition, TiO₂porousmicrospheres were applied in self-cleaning cement. The contents of the paper are listed asfollow:1. Ultrasonic spray pyrolysis method combined impregnation method was used to prepareTiO₂, Nb doped TiO₂and WO3composite Nb doped TiO₂microspheres with an averagediameter of500nm. The as-prepared microspheres had a mesoporous structure and the meanpore diameter was around8-10nm. UV-vis spectra results showed that Nb doped TiO₂spheresshowed extended visible light absorption and the spectrum onset had about88nm red shiftcompared with pristine TiO₂microspheres. However, WO3composite Nb doped TiO₂microspheres do not display a red-shifted absorption edge compared with Nb doped TiO₂microspheres. Nb doped TiO₂and WO3composite Nb doped TiO₂microspheres showed higherphotocatalytic activity for methylene blue degradation compared with that of pristine TiO₂microspheres under both visible and solar light irradiation, which could be ascribed to theextended light absorption range and the suppression of electron-hole pair recombination.Moreover, the present microspheres catalysts were advantageous in terms of their ease ofseparation from the aqueous phase, and hence they had good potential in photocatalytic reactorsdesigned on the concept of rational use of sunlight.2. TiO₂porous microspheres were applied in self-cleaning cement, which were preparedby ultrasonic spray pyrolysis method. Two model self-cleaning test methods, i.e. change ofwater contact angle after applying oleic acid to the film surface and change of the spectralabsorption of Resazurin dye, were used to characterize photocatalytic self-cleaning property ofcement films, cement films with TiO₂nanoparticles, and cement films with TiO₂porousmicropheres. Under UV light irradiation, cements film did not show any photocatalytic activity, TiO₂microspheres-cement film showed higher photocatalytic activity compared with TiO₂particles-cement film, which could be ascribed to the enhancing of the sunlight utilization andthe increasing of the amount of TiO₂participated in the reaction in cement internal and surfaceby the introducing of TiO₂porous microspheres.