1. Surface super hydrophilicity
It is considered that the super hydrophilicity of TiO2 surface is caused by the change of surface structure under illumination. Under ultraviolet irradiation, the valence band electrons of titanium dioxide are excited to the conduction band, and the electrons and holes migrate to the surface of titanium dioxide. Electrons react with Ti, and the holes react with surface bridging oxygen ions to form positive trivalent titanium ions and oxygen vacancies, respectively. At this point, the hydrolysis and separation in the air are adsorbed in the oxygen vacancy and become chemisorbed water (surface hydroxyl group). The chemisorbed water can further adsorb the water in the air and form a physical adsorption layer.
2. Surface hydroxyl group
Compared with the metal oxides of other semi-metallic semiconductors, the polarity of Ti-O bond in titanium dioxide is larger, and the water-induced polarization on the surface of titanium dioxide dissociates, which is easy to form hydroxyl groups. The surface hydroxyl group can improve the performance of TiO2 as adsorbent and various monomers, and provide convenience for surface modification.
3. Surface acidity and basicity
Aluminum, silicon and zinc oxides are often added to the modification of titanium dioxide. Aluminum or silicon oxides have no obvious acidity and basicity when they exist alone, but when they are combined with titanium dioxide, they show strong acidity and basicity. Solid Superacid can be prepared.
4. Surface electricity
When the particles are close to each other, they repel each other because of the same charge, which is beneficial to the stability of the dispersion system. For example, the surface of Al2O3 coated TiO2 has a positive charge, while the SiO2 treated TiO2 has a negative charge.