An effective method for the preparation of high temperature stable anatase TiO2 photocatalysts

Abstract

tAn efficient, rapid and straightforward method for the preparation of nitrogen and fluorine (N, F) codopedhigh temperature stable anatase using a microwave pre-treatment is reported. Using a single source,ammonium fluoride (NH4F) for both nitrogen and fluorine, effective doping of the precursor titaniumisopropoxide (TTIP) was possible. These samples were characterised for their structural and opticalproperties using X-ray diffraction (XRD), Fourier Transform IR (FTIR), Raman spectroscopy and UV–visspectroscopy. In terms of the anatase to rutile transition enhancement using a novel microwave assistedtechnique, the sample prepared in a composition of 1:8 TiO2: NH4F at 1200◦C was seen to be most effec-tive, having stable anatase present at 57.1% compared to undoped TiO2being 100% rutile from 900◦C. Thismethod involves the production of ammonium oxofluorotitanates (NH4TiOF3) at low temperatures. Theinclusion of these intermediates greatly reduces the particle size growth and delays the anatase to rutiletransition. The photocatalytic activity of these materials was studied by analysing the degradation of anorganic dye, rhodamine 6G as a model system and the rate constant was calculated by pseudo-first-orderkinetics. These results showed that the doped sample (0.0225 min−1) was three times more active thanthe undoped sample (0.0076 min−1) and over seven times faster than the commercial TiO2photocatalyststandard Degussa P-25 calcined at 1200◦C (0.0030 min−1). The formation of intermediate compounds,oxofluorotitanates, was identified as the major reason for a delay in the anatase to rutile transition