Towards an efficient and durable self-cleaning acrylic paint containing mesoporous TiO2 microspheres

Abstract

Self-cleaning paints are capable of removing undesirable substances on their surface in the presence of the incidence of light. However, the photocleaning is not selective and, in addition to pollutants, the paint matrix of the polymer can be degraded. Therefore, in order to develop a suitable self-cleaning paint formulation it is necessary to find a balance between the non-selective activity and the degradation of the film. In this study, TiO2 microspheres (MTiO2) were synthesized, characterized and incorporated into a water-based acrylic paint formulation with the aim of modulating the photocatalytic effect of TiO2 particles and increasing the paint durability. Besides the photocatalyst synthetized, commercial TiO2 particles (P25, manufactured by Evonik) were also evaluated and used as a reference. Comparatively, a commercial paint containing rutile TiO2 as a pigment was evaluated. The photocleaning efficiency of the paint films was determined by a new analysis method based on multiple cycles of adsorption and exposure to UVC light in a methylene blue solution. After the cyclic test, the stability of the paint films was evaluated using scanning electron microscopy (SEM). In aqueous suspension and under UVC light the MTiO2 showed photoactivity similar to that of P25. The incorporation of the photocatalysts in the paint films initially reduced the activity by around a factor of 5, due to limitations related to the access of the pollutants and the light to the TiO2 particles. The paint with MTiO2 incorporated was found to be more stable than the reference paint with P25 added, after the cyclic analysis. Finally, the paint containing MTiO2 exhibited degradation similar to that of the commercial paint with rutile under the same extreme conditions of the cyclic analysis.