SELF CLEANING CONCRETE

HOW IT WORKS – SELF CLEANING

Strong sunlight or ultraviolet light decomposes many organic materials in a slow, natural process. You have seen this process, for example, in the way the plastic dashboard of a car fades and becomes brittle over time. Photo catalysts accelerate this process and, like other types of catalysts, stimulate a chemical transformation without being consumed or worn out by the reaction. When used on or in a concrete structure, photocatalysts decompose organic materials such as dirt, including soot, grime, oil and particulates; biological organisms, including mold,algae, bacteria and allergens; airborne pollutants, including volatile organic compounds, including formaldehyde and benzene, tobacco smoke, and the nitrous oxides [NOx] and sulfuric oxides [SOx] that are significant factors in smog; and even the chemicals that cause odors. The catalyzed compounds break down into oxygen, carbon dioxide, water, sulphate, nitrate and other molecules that are either beneficial to or, at worst, have a relatively benign impact on the environment. Most inorganic pollutants and stains, including rust, are not catalyzed.

Titanium oxide (TiO2), the primary catalytic ingredient, is widely used as a white pigment in paint, plastics, cosmetics and a host of other products. Making it capable of photocatalysis requires manipulating the material to create extremely fine nano-sized particles with a different atomic structure than that of the ordinary pigment. At the nano scale, this type of titanium undergoes a quantum transformation and becomes a semiconductor. Activated by the energy in light, the TiO2 creates a charge separation of electrons and electron holes.

The electrons disperse on the surface of the photocatalyst and react with external substances, causing chemical reductions and oxidations and forming hydroxyl radicals that act as powerful oxidants to decompose organic compounds. Due to this oxidation reactions the pollutants are converted to less harmful substances.