What is photocatalyst (TiO2) photocatalyst (TiO2) is a semiconductor that has strong oxidation. Shining of light source can stir up oxidation-reduction reaction on its surface, and the surface will release free radicals (.OH) and (.O), at the moment, chain degradation reaction occurs between the free radicals and kinds of contaminant and bacteria each other. And the reaction can realize the functions of air purification, anti-bacteria, anti-dirtiness and deodorization, hydrophilic nature, and so on. Photocatalyst (TiO2) is a king of new environmental protection product which has high efficiency and persistent characteristics.