I am working on photocatalysis area.First of all titania is a photocatalyst.
1. It can oxidize organic materials on clothes using molecular oxygen.
2.It has surface hydroxyl gp which helps to bind with fibre.
3.It is also helpful in water splitting.
because of them surface properties of TiO2 irradiated by sola light with the spectrum below 360nm.. the mechanism involves the photogenerated high energy electron-hole pairs and their reactions with the surface-sorbed organic molecule, O2 and water yielding the formation of •OH radicals. •OH radicals are also formed via the reaction of the photo-generated holes with hydroxyl ions and water molecules adsorbed on the surface of TiO2, these radicals reacts immidiately and non-selectively with most of organics decomposing them to CO2 and water, and small fraction of simple inorganics.
ooo, and light induced superhydrophilicity:) the contact angle of the water droplet after irradiation of TiO2 decreases to almost 0 degrees.. nothing can be adsorbed and can be easilly removed:)
The band gap for titania is 3.2 eV which falls around 380 nm. Even the dissolved oxygen in water can be activated by electron-hole pair in presence of light which is responsible to generate radicals helping in oxidation.
This technology has been used for quite a while now. TiO2 particles are mass produced (degussa p25) as anti-fouling and pigments in paints, in chemical reactors as catalysts for breaking down organic molecules, as thin films for car mirrors to prevent water beading and reducing biofilm buildup. Since the 80s they have used TiO2 in car catalytic converters. They coat building windows with them to help keep them clean. Since TiO2 has a high refractive index, it is used as an intireflective coating for optical lenses and windows. It is chemically stable and relatively cheap material although I believe the cost is increasing recently. There is enough UV in sunlight (at 380nm) to excite the electrons in TiO2.
The electrons and holes have a relatively long lifetime compared to other materials because they get trapped in defect sites. This time allows the electrons and holes to migrate to the surface and oxidize or reduce O2 and H2O, which they go off and react with organic molecules.
There is a push to reduce the bandgap of TiO2 so that it will have the same photocatalytic effect with visible light. It was a great idea to combine titania with clothing, I wish I had thought of it.
The elephant in the room with this technology is this. You can treat bacteria, stains, etc with the TiO2, but what happens to that material. Is a stain just discolored but still on the fiber? If you do this say for a month, will the remains of the material be a new breeding source for more bacteria. Will the area feel different when something is not removed? Will it still feel dirty. There is literature on the good aspects, but what happens to the leftovers is not very clear. Applications such as using it on bathing suits so they don't smell wet is propbably going to be one of the better applications.
Textiles treated with TiO2 nano-particles does not allow the water or dirt particles to absorb/stick on the surface of fabric and thus cleaned by just hanging or shaking
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