Photoconductive and photocatalytic properties of ZrTiO4. Comparison with the parent oxides TiO2 and ZrO2

Orthorhombic ZrTiO4 was synthesized at 700 degrees C with a large surface area (39.5 m(2) g(-1)) and an appropriate band gap energy (3.33 eV) for the absorption of near-UV photons. Photoconductivity measurements were performed in vacuum and in oxygen to correlate the photoelectronic properties of ZrTiO4 with its photocatalytic activity. ZrTiO4 becomes a photoconductor on exposure to near-UV illumination due to electron-hole pair formation. On continuous evacuation, a very limited quantity of chemisorbed oxygen is photodesorbed because ZrTiO4 is an insulator in the dark (no accumulation of extra photoelectrons corresponding to the consumption of holes for oxygen desorption). Photoconductivity isotherms (sigma=f(P-o2)) indicate that oxygen chemisorbs as non-dissociated O-2(-) species, confirming previous results of oxygen isotopic exchange. ZrTiO4 is photoactive for isopropanol oxidation, but much less active than titania and zirconia (the parent oxides), although it has a comparable surface area and UV light absorbance. The smaller photocatalytic activity is related to the more limited capacity to photoadsorb and photodesorb oxygen and a higher electron-hole recombination. This study confirms that binary oxides are less active than pure oxides and that titania (anatase) is the most active photocatalyst. (C) 1997 Elsevier Science S.A.