One-pot synthesis of anionic (nitrogen) and cationic (sulfur) codoped high-temperature stable, visible light active, anatase Photocatalysts

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 [(NH₄) ₂SO₄], as the modification agent of the titanium isopropoxide (TTIP) precursor. A stoichiometric modification of 1:8 TTIP:(NH₄)₂SO₄ 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 TiO₂ 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.