Controlled Suppression or Enhancement of the Photoactivity of Titanium Dioxide (Rutile) Pigment

We show that the photochemical activity of 0.2micron n-TiO sub 2 (rutile) pigment can be varied, in a controllable way, by a factor of >400. The photoactivity is increased upon etching with strong mineral acids, and upon reduction, by heating the particles on which an organic film has been absorbed, to 550C, in an inert atmosphere. The photochemical activity is suppressed by oxidation in air at 550C, by chemisorption of less than 1/10 of a monolayer of Fe sup 2+ and Fe sup 3+ ions, and by lattice defects that are introduced by mechanical processes such as milling. Specific processes are described to increase, by an order of magnitude, the photochemical activity of a commercial pigment and to suppress its photochemical activity by a factor of >50.