A photo-catalyzer for deodorizing, cleaning, sterilizing, and water purifying operations includes a substrate, a titanium dioxide film disposed on the substrate and functioning as a photo-catalyst, and a light-emitting diode disposed adjacent to the titanium dioxide film and producing ultraviolet light having a wavelength from 360 to 400 nm onto the titanium dioxide film. The photo-catalyzer can be used in places where there is no sunlight because it is optionally provided with a light-emitting diode. The light-emitting diode does not require a large installation space because it is an extremely small light-emitting device. Hence, the photo-catalyzer has a compact structure and can be used easily anywhere, including small places. The substrate can be fabricated into a variety of useful appliances to take advantage of the strong oxidizing properties of the photo-catalyzer. Devices comprising a photo-catalyzer may be used for deodorizing, destroying or repelling micro-organisms, and including undertaking air or water purification.