**3. Conclusions**

Surface treatment of TiO<sup>2</sup> particles is one of the most important steps in the production of TiO<sup>2</sup> pigment. It is a delicate and complex process. Process parameters such as pH and temperature have to be carefully controlled, as this is essential to ensure the formation of uniform oxide coatings and achieving the desired useful features. Surface-treated TiO<sup>2</sup> particles were prepared starting from various precursors by the chemical liquid deposition method. Uniform hydroxide layers formed on the surfaces of the TiO<sup>2</sup> particles under mild hydrolysis rate of, for example, sodium aluminate, aluminum sulfate or sodium silicate in gel precipitation and aging. The morphology of the layers was significantly affected by the temperature and pH value of the reaction solution. Formation of thin and uniform hydroxide layers influenced optical and electrochemical properties. Surface-treated particles altered their electrokinetic behavior in a way similar to the coating material, suggesting formation of a complete hydroxide layer on the TiO<sup>2</sup> surface. We can conclude that inappropriate pH conditions can lead to undesirable phases of hydroxides or to an incomplete layer. By applying a dense silica layer of colorless alumina phosphate, photoactivity of TiO<sup>2</sup> pigments was successfully suppressed.
