What is photocatalysis?
In photocatalysis there is "photo" meaning light and "catalysis" which promotes an enzymatic reaction.
The photocatalyst picks up a photon of light, which causes the transfer of an electron inside the semiconductor. At the same time, oxygen O2 is reduced as a superoxide ion O2°- and H2O water is decomposed into H+ and OH-. The 2 entities O2°- and OH - will oxidize the organic pollutant and thus destroy it.
Titanium dioxide or TiO2
There is a lot of photocatalysts (TiO2, ZnO, CeO2, ZrO2, SnO2, CdS, ZnS ...) but the one with the best performance / cost ratio is TiO2. In its anatase crystallographic form, it is activated by wavelengths less than 390 nm. These wavelengths represent only 4% of the solar energy, but the absorption spectrum can be moved to more favorable wavelengths by adding other compounds: this is called "doping ".
Organic substances are degraded by photocatalysts. The main applications will be dioxins and persistent organic products (such as pesticides), volatile organic compounds (such as formaldehyde), sulfur-containing odorants and microorganisms such as bacteria, fungi and viruses. They therefore also have antimicrobial activity.
Photocatalysts can also destroy acid gases NO, NOX, SO2 and ozone (O3).
Titanium dioxide can be mixed with other components or fastened to various substrates such as glass, ceramics, steel or polymers. One of the most spectacular applications is undoubtedly the development of self-cleaning glazing. A thin layer of TiO2 associated with hydrophilic compounds covers the glass. In the presence of sunlight, the organic matter deposited on the glass is decomposed by photocatalysis. Because the surface is hydrophilic it prevents the formation of drops on the surface of the glass and the water forms a film which flows easily.
It is precisely the trickling water that carries with it the waste coming from the destruction of organic matter. In case of lack of rain, it is necessary to water the windows regularly. Moreover, it eliminates mineral waste not destroyed by TiO2 and which can prevent their action by accumulation. This type of glazing is found in large towers where accessibility is difficult.
Pavement tiles, building
The TiO2 introduced into the pavement coating and tested in situ seems to be of interest during peaks of pollution, sometimes showing up to 40% NOx reduction. The results are sometimes difficult to interpret. In all cases, the activity is closely dependent on the sunlight and the fouling state of the coating.
There are self-cleaning cements.
When TiO2 is introduced in ski boots, it removes odors when illuminated by UV.
Water and air treatments
There are systems of water purification and indoor air purification based on photocatalysis.
Applications in the medical field are under consideration.
Ouvry self-decontaminating NRBC outfits
The SELDEC project 2009-2011
It was a R & D project developed by the ANR (National Research Agency) program of the CSOSG program (Concepts, Systems and Tools for Global Security).
SELDEC: Self-decontaminating multispectral protective materials under natural illumination visible/solar or artificial UV-A.
The partners were OUVRY SAS (coordinating partner), LPMT (Laboratory of Physics and Mechanics of Textiles of Mulhouse), LMSPC Laboratory of materials, surfaces and processes for catalysis (Strasbourg) and SDIS 91.
The aim was to propose new materials for protective clothing for workers inteded to work in environments contaminated with chemical and biological agents. The filtering textile of Ouvry combined with a photocatalytic coating based on TiO2 is intended to improve the protection of first-responders by creating a self-regenerating filtering system.
The group has developed a technique for the functionalization of the textile by the layer-by-layer method (LBL). It consists in applying, to the negatively charged support, a positively charged polyelectrolyte layer and a negative TiO2 nanoparticles, layer. Then, a new polyelectrolyte layer is deposited following by a new TiO2 layer: it is thus possible to deposit several layers whose electrostatic cohesion allows a high mechanical strength: the product can be washed in washing machine. The well known technique of the textile industry by immersion / padding has also been tested successfully. You will find the main results obtained by following the followinglink
The Safecoat project 2012-2015
This feasibility study was followed by another CSOSG ANR project called "Safecoat", which exact title was: photocatalysts and functionalized self-decontaminating textiles under sunlight for individual protection against toxic agents.
The partners were Ouvry, the LPSPC and the Charles Sadron Institute (ICS) in Strasbourg.
The targeted toxic agents were the war chemical agents and Bacillus spores, biological agent of the threat. Protective clothing for first responders was one of the critical applications.
Scientist succeded to dope photocatalyst in order to make it works in sunlight. Moreover, the industrial feasibility of the functionalization of the filtering textiles has been demonstrated. These results open up a wide range of applications for the company Ouvry and show that R & D is a very important components of our activities.
We can follow this linkwith profit