New approach of modifying the anatase to rutile transition temperature in TiO₂ photocatalysts

In pure synthetic titanium dioxide, the anatase to rutile phase transition usually occurs between the temperatures of 600 °C and 700 °C. The phase transition temperature can be altered by various methods, including modifying the precursor or by adding dopant or modifier to the TiO₂ sample. In an attempt to investigate the phase transition using aromatic carboxylic acids, the current study examines the impact of increasing concentrations of benzoic acid (1:0, 1:1, 1:4 and 1:8 molar ratio TiO₂:benzoic acid) on anatase to rutile transition. The samples were characterised using Raman spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) studies. At 500 °C, all samples contained only anatase. At 600 °C, the 1:1, 1:4 and 1:8 samples contain only anatase and the control (which contains no modifier) was a mixture of 27% anatase and 73% rutile. At 700 °C, the 1:1 molar ratio sample contained 50% anatase/rutile, 1:4 and 1:8 molar ratio samples were observed to have a majority of anatase, 76% and 71% respectively. When the temperature was increased to 800 °C, the sample with the 1:4 molar ratio contained 10% anatase and at the same temperature the 1:8 ratio sample contained 7% anatase; the remaining samples (1:0 and 1:1) at this temperature contained only rutile. These results show that there is a significant % anatase still present when the doped samples were calcined to 700 °C when compared with the control (100% rutile). There are small amounts of the anatase phase in the 1:4 and 1:8 samples at 800 °C. Therefore, benzoic acid has induced a delay in the rutile formation.