Photocatalyst means a substance that absorbs light energy and causes a photochemical reaction, and theoretically, organic pollutants can be completely decomposed into water and carbon dioxide. The typical optical catalyst is titanium dioxide (TiO2). TiO2 is used more frequently because it is resource-rich and cheap, has good durability, and abrasion resistance as an optical catalyst. There is no concern about secondary pollution when disposed of as a safety toxic substance. Especially considering the photocatalytic conditions and activity, it can be used semi-permanent even if it receives light, has strong sterilization due to higher oxidation power than chlorine or ozone, and eco-friendly because it breaks down all organic materials into carbon dioxide and water. Therefore, it has great ability in air purification, anti-staining function, hydrophilic function, water purification, deodorization, and antibacterial function.