EFFECT OF POTASSIUM ON THE SURFACE-POTENTIAL OF TITANIA

The surface potential, chi, of several commercial titania powders has been measured by the vibrating condenser method in the temperature range 100-450-degrees-C in air. The K impurity detected by XPS on some of titanias lowers the chi value of TiO2 considerably. A series of K-doped TiO2 anatase samples containing from 1.1 to 11 K atoms nm-2 was prepared and examined by surface potential and XPS techniques. The surface potential of anatase decreases linearly with increasing potassium content up to ca. 2.4 K atoms nm-2 , and then remains constant. The surface potential of K-doped samples varies to a smaller extent with temperature compared with undoped anatase. On the basis of the surface potential and XPS data obtained, it is suggested that the mode of K deposition on the surface of anatase changes at a coverage of about 2 K atoms nm-2.