Thermally stable SiO2@TiO2 core@shell nanoparticles for application in photocatalytic self-cleaning ceramic tiles

Photocatalyst-coated self-cleaning ceramic tiles are in high demand for indoor and outdoor applications aimed at keeping a clean environment. Their industrial processing, however, often requires firing at temperature (1000-1200 °C) much higher than the thermal stability limits of common photocatalysts (<1000 °C) which results a significant loss in self-cleaning activity of the tiles. To address this issue, we have coated commercial ceramic tiles with thermally stable core@shell SiO2@TiO2 particles, which even after single-fire industrial treatment (1000-1140 °C), exhibit excellent self-cleaning activity, much higher than that of control tiles prepared with commercial benchmark P25 TiO2 photocatalyst. Importantly, the photocatalytic activity of SiO2@TiO2 particles, in both powder form and as coatings on ceramic tiles, enhanced with the increase in calcination temperature (to as high as 1000-1140 °C) which is in sharp contrast to the normal photocatalytic behavior of unsupported TiO2. This article explores in details the exceptionally high and industrially relevant thermal stability of silica-supported anatase nanocrystals (5 nm) (SiO2@TiO2) against phase transition and crystallite growth and brings new insight into the effect of core@shell configuration on the thermal stability and photoactivity of SiO2@TiO2 particles. A comprehensive discussion on the relationship between core@shell structure, thermal stability and photoactivity is presented. These SiO2@TiO2 particles with ideal physicochemical characteristics (small phase-pure anatase nanocrystals with higher resistance towards crystallite growth, phase transformation or surface-area loss upon calcination) are ideal photocatalytic materials for efficient photodegradation of organic pollutants for effective environmental remediation and other applications that involve high-temperature processing such as self-cleaning coatings and photocatalytic ceramics.