SURFACE CHARACTERIZATION OF ZIRCONIUM TITANATE (ZRTIO4) POWDER BY MEASUREMENTS OF ELECTRICAL PHOTOCONDUCTANCE AND PHOTOASSISTED OXYGEN-ISOTOPE EXCHANGE

The photosensitivity of a ZrTiO4 sample (33 m2/g) prepared by a sol-gel method has been assessed in the presence of O2 by both photoconductance and oxygen isotope exchange (OIE) measurements at room temperature at wavelengths > 290 nm. For oxygen pressures P(O2) < ca. 13.3 Pa, the steady-state photoconductance sigma of ZrTiO4 was unaffected by P(O2), which indicated that the direct recombination of the photoproduced charges played the dominant role. At higher pressures, sigma varied as the reciprocal of P(O2), which was consistent with the fact that the electronic equilibrium was then governed by O2 + e- --> O2-. OIE over ZrTiO4 occurred predominantly via the overall mechanism which involves the exchange of two surface oxygen atoms for each exchange act. It was very slow as compared with OIE over photocatalytically active anatase samples which, in addition, occurs via another mechanism. These results allow one to predict that this ZrTiO4 sample is a poorly active photocatalyst for oxidations involving gaseous oxygen, and further illustrate the interest of sigma and OIE measurements to evaluate the photosensitivity of semiconductor oxide samples.