How do sterilization and deodorization, which were mentioned in the section on the effects of ARC-FLASH, occur at the surface of the photocatalytic titanium dioxide? The explanation here is based on theories that have been clarified so far; however, basic studies of the precise mechanism are still under way.
Oxidation-reduction reactions occur repeatedly on a surface treated with ARC-FLASH. Air is needed for environmental purification using titanium dioxide. Air always contains oxygen and water vapor, which are also involved in the reaction mechanism.
|(1)||Photocatalysis is initiated when titanium dioxide is exposed to UV rays. This is called optical solid surface or interface reaction.
Titanium dioxide absorbs UV rays, and electrons and holes are generated inside it. Electrons and holes near the surface are involved in reaction. The generation of many electrons and holes leads to a higher reaction effect.
|(2)||The generated holes have strong oxidizability, and generate hydroxyl radicals by reacting with water at the surface of the titanium dioxide.|
|The generated hydroxyl radicals have strong oxidizability and cause oxidative reactions with organic compounds. In the presence of oxygen, radicals of the intermediates of organic compounds and oxygen molecules induce a radical chain reaction and consume oxygen. Organic compounds are then decomposed and eventually turn into carbon dioxide and water.|
|(3)||The generated electrons generate superoxide anions by causing a reductive reaction with surface oxygen.|
|The generated superoxide anions form oxides by adhering to the intermediates of the oxidation reaction or turn into hydrogen peroxide and then into water. O is also generated in the air and directly affects the carbon-carbon bond of organic matter.|
|(4)||Organic matter is a causative agent of germs and odors. Because organic matter is usually more oxidizable than water, holes are more likely to be used for oxidation of organic compounds and the recombination rate of carriers (holes and electrons) decreases when the concentration of organic matter is higher.Under the condition where all of the spaces are filled, the transfer of electrons to oxygen molecules at the reduction site become the rate-determining step of the entire photocatalytic reaction. In other words, the efficiency of the reaction is improved by facilitating the transfer of electrons into oxygen molecules.|