Synthesis of high-temperature stable anatase TiO₂ photocatalyst

In the absence of a dopant or precursor modification, anatase to rutile transformation in synthetic TiU2 usually occurs at a temperature of 600-700 °C. Conventionally, metal oxide dopants (e.g., Al₂O₃ and SiO₂) 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 °C with use of a 1:1 Ti(OPr)₄:urea composition and 11 % anatase composition is retained even after calcining the powder at 900 °C. By comparison a sample that 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 °C compared to the unmodified sample. 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 to 0.224 cm³/g) and average pore diameter (11 to 30 nm) compared to the standard sample. Samples prepared with 1:1 Ti(OPr)₄:urea composition calcined at 900 °C 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 (0.027 min^-1, decoloration in 120 min) to the urea-modified sample (0.073 min^-1, decoloration in 50 min).