SELF CLEANING TEXTILES
The self-cleaning fabrics work using the photocatalytic properties of titanium dioxide, compound used in many new nanotechnology solar cell applications. The fabric is coated with a thin layer of titanium dioxide particles that measure only 20 nanometers in diameter. When this semi-conductive layer is exposed to light, photons with energy equal to or greater than the band gap of the titanium dioxide excite electrons up to the conduction band. The excited electrons within the crystal structure react with oxygen atoms in the air, creating free-radical oxygen. These oxygen atoms are powerful oxidizing agents, which can break down most carbon-based compounds through oxidation-reduction reactions. In these reactions, the organic compounds (i.e. dirt, pollutants, and micro organisms) are broken down into substances such as carbon dioxide and water. Since the titanium dioxide only acts as a catalyst to the reactions, it is never used up. This allows the coating to continue breaking down stains over and over.
Starting with photocatalysts. It is catalytic self-cleaning process. In this process Nano-sized , titanium dioxide and zinc oxide are used for imparting self cleaning and anti-bacterial properties .The fabric is coated with a thin layer of titanium dioxide particles heaving 20 nanometers diameter. Titanium dioxide is a photocatalyst; when it is illuminated by light of energy higher than its band gap, electrons in TiO2 will jump from the valence band to the conduction band, and the electron (e) and electric hole (h+) pairs will form on the surface of the photocatalyst. The negative electrons and oxygen will combine to form O2 . radical ions, whereas the positive electric holes and water will generate hydroxyl radicals OH.. Since both products are unstable chemical entities, when the organic compound i.e. dirt, pollutants, and micro organisms falls on the surface of the photocatalyst it will combine with O2 – and OH- and turn into carbon dioxide (CO2) and water (H2O).Since the titanium dioxide acts as a catalyst, so it is never used up. This is how the coating continues breaking down stains over and over. Zinc oxide is also a photocatalyst, and the photocatalysis mechanism is similar to that of titanium dioxide.