Improved high temperature stability of photo-active sulphur doped anatase TiO2

RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required according to the journal that you are submitting your paper to) TITLE RUNNING HEAD 'Improved stability of anatase TiO 2 ' CORRESPONDING AUTHOR FOOTNOTE *[email protected] 2 ABSTRACT: 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.