In the absence of a dopant or precursor modification, anatase to rutile transformation in synthetic TiO 2 usually occurs at a temperature of 600 ºC to 700 ºC. Conventionally, metal oxide dopants (e.g. Al 2 O 3 and SiO 2 ) are used to tune the anatase to rutile transformation. A simple methodology is reported here to extend the anatase rutile transformation by employing various concentrations of urea.XRD and Raman spectroscopy were used to characterize various phases formed during thermal treatment. A significantly higher anatase phase (97%) has been obtained at 800 ºC using a 1:1 (Ti (OPr) 4 : urea) composition and 11% anatase composition is retained even after calcining the powder at 900 ºC. On comparison a sample which has been prepared without urea showed that rutile phases started to form at a temperature as low as 600 °C. The effect of smaller amounts of urea such as 1:0.25 and 1:0.5 (Ti (OPr) 4 :urea) has also been studied and compared. The investigation concluded that the stoichiometric modification by urea 1:1 (Ti (OPr) 4 :urea) composition is most effective in extending the anatase to rutile phase transformation by 200 ºC compared to the unmodified samples. In addition, BET analysis carried out on samples calcined at 500 °C showed that the addition of urea up to 1:1 (Ti (OPr) 4 :urea) increased the total pore volume (from 0.108 cm 3 /g to 0.224 cm 3 /g) and average pore diameter (11 nm to 30 nm) compared to the standard sample. Samples prepared using 1:1 (Ti (OPr) 4 :urea) composition calcined at 900 ºC show significantly higher photocatalytic activity compared to the standard sample prepared under similar conditions. Kinetic analysis shows a marked increase in the photocatalytic degradation of rhodamine 6G on going from the standard sample (0.016 min , decoloration in 50 mins).

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Of the various forms of titania (anatase, rutile and brookite) anatase is found to be the best photocatalyst. Without any chemical additives, the anatase to rutile transformation in pure synthetic titania usually occurs at a temperature range of 600 to 700 °C. High temperature (≥800 °C) stable photoactive anatase titania is required for antibacterial, application in building materials. A simple methodology to extend the anatase phase stability by modifying the titanium isopropoxide precursor by sulphur modification using sulphuric acid is presented. Chemical synthesis by sol-gel method involved the reaction of titanium tetraisopropoxide (TTIP) with sulphuric acid (H 2 SO 4 ), followed by hydrolysis and condensation. The xerogel formed after drying was subjected to further calcination at different temperatures. 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 characterized by XRD, DSC, Raman spectroscopy, XPS and BET surface area analysis.Sulphur modified samples showed extended anatase phase stability up to 900 ºC, while the control sample prepared under similar conditions completely converted to rutile phase at 800 ºC. 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 the control sample and it shows 100 % anatase at 800 °C and 20 % anatase at 900 ºC. Samples of 1:4 TTIP:H 2 SO 4 composition calcined at various temperatures such as 700, 800, 850 and 900 ºC showed significantly higher photocatalytic activity compared to the control sample. The 1:4 TTIP:H 2 SO 4 composition calcined at 850 ºC showed the highest photoactivity and it decolorized the rhodamine 6G dye within 12 minutes (rate constant 0.27 min -1 ) whereas the control sample prepared under identical condition decolorized the dye after 80 minutes (rate constant 0.02 min -1 ). It was also observed that the optimal size for highly photoactive anatase crystal is ca. 15 nm. XPS studies indicated that the retention of the anatase phase at high temperatures is due to the existence of small amounts of sulphur up to 900 °C.