Attention is now focused on the quality of the air indoors, which was not part of the conversation until now. Above all, deodorization and sterilization systems that utilize photocatalysts are beginning to play an active role in various places in the city. This system that utilizes ultraviolet rays is able to suppress substances, bacteria, viruses, etc. that cause bad odor, when they come into contact with the photocatalyst by exposing the photocatalyst to ultraviolet rays. Recently, it has begun to be used in places where cleaner air is required, such as hospitals and nursing care facilities, and in spaces where many different people gather, such as railroad cars, hotels, schools, nurseries, and corporate offices.