Mixed-phase photocatalytic nanocrystalline TiO2 powders prepared by flame spray pyrolysis

Mixed-phase titanium dioxide (TiO2) nanostructured powders with different structural characteristics (i.e. primary particle size, crystalline phase, specific surface area, porosity and morphology) were synthesized by Flame Spray Pyrolysis (FSP) using titanium(IV) isopropoxide (TTIP) as precursor. The influence of the synthesis parameters on the structural properties of the powders was investigated by means of Raman spectroscopy, XRD, BET, SEM and UV-VIS absorption analysis. A decrease of the primary particle size from ca. 21 to 7 nm, together with an increase in the brookite content and in the BET surface area from ca. 70 up to 250 m2 g-1 were observed by increasing the molar ratio between the dispersion oxygen gas and the TTIP fed into the flame. The photocatalytic activity of the as-prepared TiO2 powders was investigated employing formic acid decomposition in aqueous suspension as test reaction and related to both the synthesis conditions and the structural properties of the photocatalysts. With the TiO2 powders synthesized with higher O2/TTIP flux molar ratio the formic acid photomineralization preceded at a constant rate, with a zeroth-order rate constant which significantly overcomes that obtained with commercial Degussa TiO2-P25.