Influence of TiO₂ incorporation on controlled crystallization and photocatalytic activity of borosilicate glass–ceramics

TiO₂-containing glass–ceramics were synthesized through controlled crystallization of a silicate-based parent glass to investigate the correlation between phase evolution and photocatalytic performance. The as-quenched samples exhibited fully amorphous structures, whereas subsequent heat treatments (570–1000 °C) induced controlled crystallization of anatase and rutile TiO₂ phases. Differential thermal analysis (DTA) was employed to optimize the crystallization heat-treatment schedule. Scanning electron microscopy (SEM) revealed the formation of fine TiO₂ nanocrystals at lower crystallization temperatures (570–584 °C), whereas grain coarsening and increased rutile content were observed at higher temperatures. Diffuse reflectance spectroscopy (DRS) indicated a gradual narrowing of the optical band gap from 3.67 eV in the sample with low TiO₂ content to approximately 3.26 eV in the sample with high TiO₂ content, attributed to variations in phase composition. The photocatalytic activity of the glass–ceramics was evaluated using the degradation of methyl orange under UV–visible irradiation. Among the studied samples, the glass-ceramic containing the highest TiO₂ content (20.4 wt%) and heat-treated at 570°C for 5 h, exhibited the highest photocatalytic degradation efficiency. This behavior highlights the combined effect of composition and heat treatment on the formation of active crystalline phases and the resulting photocatalytic performance. These findings demonstrate that controlled crystallization is an effective strategy for tailoring the phase composition and photocatalytic performance of TiO₂-based borosilicate glass–ceramics.