TiO2 Supported on Kaolinite via Sol–Gel Method for Thermal Stability of Photoactivity in Ceramic Tile Produced by Single-Firing Process

Anatase is well known for its photocatalytic properties. However, it can be irreversibly transformed into rutile at temperatures above 600–850 °C. This is a major limitation for ceramic tiles with self-cleaning properties, which are usually single-fired at 1100–1250 °C. To avoid this issue, functionalized tiles are often produced by double firing, where the second firing stays below 850 °C. Supporting TiO2 on kaolinite helps to stabilize the anatase phase even at temperatures above 850 °C. In this study, a photocatalytic coating was specially developed to be suitable for the single-firing ceramic tile process. TiO2 and TiO2 with Nb2O5 (from 0 to 12 wt.%) were supported on kaolinite. This material was mixed with a glass frit to create a surface texture typical of ceramic tiles. The coated tiles were single-fired at 1185 °C. The self-cleaning performance was evaluated using contact angle (CA) measurements and methylene blue (MB) degradation under UV-A light, on both unpolished and polished surfaces. The polished sample containing 12 wt.% TiO2 showed the best photocatalytic activity: it degraded 57% of MB and the contact angle decreased from 64° to 30° after UV-A exposure. XPS, FTIR, and FEG-SEM analyses confirmed the effective presence of TiO2. The results demonstrate that kaolinite-supported TiO2 is a promising approach for producing self-cleaning ceramic tiles using a single-firing process.