The photocatalytic air purifier is based on photocatalytic oxidation (PCO), an emerging air purifier technology that converts fine particles and toxic gasses into safer compounds. Photocatalytic air cleaning uses broad spectrum ultraviolet light, which energizes a thin-film titanium dioxide-based semiconductor catalyst, in the presence of water, creating hydroxyl radicals and super-oxide ions which oxidize finer particulate matter, volatile organic compounds (VOCs), and destroy microorganisms adsorbed on the catalyst surface. Now that everything is perfectly clear, we can all go home right? Maybe we should try again. Lets analyze this animal one concept at a time; a real bright light shines on a wet metal thing which makes tiny pac-man people that get rid of bad stuff stuck on the surface and turn it into carbon dioxide and water. When the pac-people are done, they turn back into to oxygen and hydrogen. That better? A high-intensity broad spectrum ultraviolet lamp, with germ killing wavelengths included, is the first building block of photocatalytic air purification technology. A catalyst is a substance that can accelerate a chemical reaction without being used up itself. The catalyst material in photocatalytic air purifiers is titanium dioxide, TiO2. This semiconductor is applied as a thin film on aluminum or ceramic substrate. When a semiconductor is illuminated with light of certain wavelengths, electrons in the materials surface are excited, coming loose and starting chain reactions. This excess energy ends up splitting nearby water vapor molecules into two parts, hydroxyl radicals and super-oxide ions. These free radicals are like tiny pac-people from the old video game: little round guys with enormous mouths that gobble up everything in their way. Hydroxyl radicals are among the most active oxidizers in the world, stronger than chlorine, ozone, and peroxide, and therefore very short lived. Superoxide, not the same as ozone, is created by the addition of one electron to oxygen. This free radical has a "long" half-life: less than one second. Toxic substances, like germs and volatile organic compounds, are coupled together by carbon-carbon, carbon-oxygen or carbon-hydrogen bonds. Oxidizers chop these bonds and break the molecule into smaller compounds. This continues until only carbon dioxide and water are left. Since the process happens at the photocatalyst surface, and the oxidizers quickly expend their energy, photocatalytic air purification is safer than existing ozone-based oxidation systems. Only the ultraviolet bulb needs replacing, about once a year, so maintenance costs on these air cleaners are low. This is an exciting area, with new science and improved products almost daily. There are even photocat lightbulbs and paints that eat pollution. Photocatalytic air purifiers are the air cleaning machines of the future. |
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