IR spectroscopy was used to investigate the surface properties of anatase gels contg. ≤1% K2O, one of the additives most commonly used to give TiO2 pigmentary characteristics. K2O mostly collects at the surface of the material, as revealed by the spectral behavior of surface hydroxyls and of surface sulfate contaminants. During the thermal treatment leading to the pigmentary material, K2O progressively modifies TiO2 surface acidity, so that on the low-surface-area final product no Ti ions are revealed by suitable admols. (pyridine, CO), but only coordinatively unsatd. K ions, acting as weak Lewis centers. The surface modifications caused by K2O are slowly reversible on contact with H2O vapor.
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