When sunlight comes in and strikes a photocatalyst, like TiO2, or titanium dioxide, it creates these really reactive oxygen species, like superoxides, hydrogen peroxide and hydroxyl radicals.
태양광이 들어와  이산화티타늄(TiO2)같은 광촉매제를 충돌시키면 반응하여 활성산소가 생성되는데 초산화물, 과산화수소와  하이드록실기 같은 것들입니다.