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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Nanoparticles of ZnO were prepared by the reaction of ethanolic solutions of zinc acetate and oxalic acid followed by drying (80 uC) and calcination (500 uC). Subsequently varistor materials were fabricated from this nanoparticular ZnO via two separate routes:-a) from a ''core shell'' material using metal salts as additives; b) by using a conventional solid state mixing of metal oxides. Sintering (1050 uC) and subsequent electrical studies were carried out for each of these samples and they were compared with commercial varistor samples prepared under similar conditions. ''Core shell'' type varistor material showed considerably higher breakdown voltage (V c~8 50 ¡ 30 V mm 21 ) as compared to a sample prepared by mixing with metal oxides (V c~6 83 ¡ 30 V mm 21 ) or commercial varistor discs (V c~5 07 ¡ 30 V mm 21 ). The high breakdown voltage obtained is attributed to the formation of more varistor-active grain boundaries per unit area.

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.

An efficient and straightforward method for the preparation of nitrogen and sulfur (N, S) codoped high-temperature stable, visible light active, anatase titania is reported. For the first time simultaneous nitrogen and sulfur doping was achieved using a single source, ammonium sulfate [(NH 4 ) 2 SO 4 ], as the modification agent of the titanium isopropoxide (TTIP) precursor. A stoichiometric modification of 1:8 TTIP:(NH 4 ) 2 SO 4 composition (TNS8) was found to be the most effective in extending the stability of anatase to higher temperatures. This particular modification resulted in 100% anatase at 850°C and 41% anatase at 900°C, whereas the control titania contained only 12% anatase at 700°C and completely transformed to rutile at 800°C. Codoped (N, S) titania was investigated by a range of characterization techniques including XRD, Raman spectroscopy, XPS, and FTIR. XPS indicated the existence of nitrogen as an anion dopant and sulfur as a cation dopant within the TiO 2 lattice. The UV/visible and visible light photocatalytic studies were carried out using the rhodamine 6G dye as a model system. The visible light photocatalytic activity of the TNS8 sample calcined at 850°C was double that of Degussa P25, and the rate constant calculated by pseudo-first-order kinetics was 0.019 min -1 for the TNS8 sample and 0.008 min -1 for Degussa P25. This higher photocatalytic activity was attributable to a combination of improved anatase phase stability, higher surface area, and codoped (N, S) titania lattice. Moreover, this codoped (N, S) sample also exhibits excellent photocatalytic activity under UV/visible light.

Sol-gel coatings which elute bioactive silver ions are presented as a potential solution to the problem of biofilm formation on indwelling surfaces. There is evidence that high-temperature processing of such materials can lead to diffusion of silver away from the coating surface, reducing the amount of available silver. In this study, we report the biofilm inhibition of a Staphylococcus epidermidis biofilm using a low-temperature processed silver-doped phenyltriethoxysilane sol-gel coating. The incorporation of a silver salt into a sol-gel matrix resulted in an initial high release of silver in de-ionised water and physiological buffered saline (PBS), followed by a lower sustained release for at least 6 days-as determined by graphite furnace-atomic absorption spectroscopy (GF-AAS). The release of silver ions from the sol-gel coating reduced the adhesion and prevented formation of a S. epidermidis biofilm over a 10-day period. The presence of surface silver before and after 24 h immersion in PBS was confirmed by X-ray photoelectron spectroscopy (XPS). These silver-doped coatings also exhibited significant antibacterial activity against planktonic S. epidermidis. A simple test to visualise the antibacterial effect of silver release coatings on neighbouring bacterial cultures is also reported. r

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In pure synthetic titanium dioxide, the anatase to rutile phase transition usually occurs between the temperatures of 600 °C and 700 °C.