Superhydrophilic surface

It is concluded that the superhydrophilicity of TiO2 surface is caused by the change of its surface structure under the condition of illumination. Under ultraviolet irradiation, TiO2 valence band electrons are excited to the conduction band, and electrons and holes migrate to the surface of TiO2, forming electron hole pairs on the surface, electrons react with Ti, and holes react with surface bridging oxygen ions to form positive trivalent titanium ions and oxygen vacancies respectively. At this time, the hydrolytic separation in the air is adsorbed in the oxygen vacancy, becoming chemisorbed water, and the chemisorbed water can further adsorb the water in the air to form a physical adsorption layer.

Surface hydroxyl group

Compared with the metal oxides of other semi-metallic materials, the Ti-O bond in TiO2 has a larger polarity, and the water adsorbated on the surface is dissociated due to polarization, which is easy to form hydroxyl. The surface hydroxyl group can improve the performance of TiO2 as adsorbent and various monomers, and provide convenience for surface modification.

Surface acid-base

TiO2 is often modified by adding Al, Si, Zn and other oxides. When the oxides of Al or Si exist alone, they have no obvious acid-base, but when combined with TiO2, they show strong acid-base, and solid superacid can be prepared.

Surface electricity

TiO2 particles in liquid (especially polar) media will adsorb opposite charges due to the surface charge and form a diffused double layer, so that the effective diameter of the particles increases. When the particles are close to each other, they repel each other due to the same charge, which is conducive to the stability of the dispersion system. For example, TiO2 coated by Al2O3 has a positive charge on the surface, while TiO2 treated with SiO2 has a negative charge.