Key points are not available for this paper at this time.
Of the various forms of titania (anatase, rutile, and brookite), anatase is reported to be the best photocatalyst. The anatase-to-rutile transformation in pure synthetic titania usually occurs at a temperature range of 600−700 °C. High-temperature (≥800 °C) stable anatase titania photocatalyst is required for antibacterial applications in building materials. A simple methodology to extend the anatase phase stability by modifying the titanium isopropoxide precursor with sulfur modification using sulfuric acid is presented. Various TTIP/H 2 SO 4 molar ratios such as 1:1, 1:2, 1:4, 1:8, and 1:16 were prepared, and these samples were characterized by XRD, DSC, Raman spectroscopy, XPS, and BET surface area analysis. Sulfur-modified samples showed extended anatase phase stability up to 900 °C, while the control sample prepared under similar conditions completely converted to rutile at 800 °C. Stoichiometric modification up to 1:4 TTIP/H 2 SO 4 composition (TS4 ) was found to be most effective in extending the anatase-to-rutile phase transformation by 200 °C compared to that of the control sample and showed 100% anatase at 800 °C and 20% anatase at 900 °C. The TS4 composition calcined at various temperatures such as 700, 800, 850 and 900 °C showed significantly higher photocatalytic activity compared to the control sample. The TS4 composition calcined at 850 °C showed visible light (sunlight) photocatalytic activity, and it decolorized the rhodamine 6G dye within 35 min (rate constant, 0.069 min −1 ), whereas the control sample prepared under identical conditions decolorized the dye only after 3.5 h (rate constant, 0.007 min −1 ). It was also observed that the optimal size for the highest photocatalytically active anatase crystal is ∼15 nm. XPS studies indicated that the retention of the anatase phase at high temperatures is due to the existence of small amounts of sulfur up to 900 °C.
Periyat et al. (Thu,) studied this question.