| Summary: |
Nitrogen oxides (NOx) are in the origin of various environmental problems. It is well known that NOx cause acid rain and photochemical smog. There has recently been a demand for technology for the reduction of NOx from the atmosphere. The photocatalytic oxidation of NOx using TiO2 as photocatalyst has been reported to be one solution to the problem. In the presence of water, NOx is oxidized to nitric and nitrous acid. Moreover, for TiO2 to maintain its photocatalic activity it is necessary to remove these oxidation products. This can be done if these acids are made to react with substances such as calcium carbonate or calcium oxide.
Decorative paints are paints used for coating buildings for decorative, functional and protective reasons. A high quality paint can incorporate up to 20% (w/w) of TiO2 (mainly rutile) and about the same amount of fillers, such as calcium carbonate or talk. TiO2 is used for give to the paint opacity and whiteness while filers are necessary for helping on the opacity and for lowering the price.
It seems then that paints can serve for controlling the NOx formed in cities, helping to control the air pollution. This is not the case because the TiO2 photoactivity promotes the degradation of the resin at the paint surface. The TiO2 used in paints is then treated with a very thin coating such as alumina and has no photoactivity.
NOx are essentially formed due to cars circulation. A polluted city can have NOx concentrations in the range of 310 µg/m3 (e.g. Prague in 1995). A recent study showed that 1 kg of TiO2/CaO (1:1) can treat about 5x106 m3 of air containing 0.06 ppm of NOx. Using buildings coating for treating the ambient air is a completely innovative and promising solution. The largest Portuguese paint company, CIN, uses each year about 1.5x106 kg of TiO2 for decorative exterior paints and have about 30% of the market. These data show that the produced paint is potentially able to photooxidise a significant fraction of the NO  |
Summary
Nitrogen oxides (NOx) are in the origin of various environmental problems. It is well known that NOx cause acid rain and photochemical smog. There has recently been a demand for technology for the reduction of NOx from the atmosphere. The photocatalytic oxidation of NOx using TiO2 as photocatalyst has been reported to be one solution to the problem. In the presence of water, NOx is oxidized to nitric and nitrous acid. Moreover, for TiO2 to maintain its photocatalic activity it is necessary to remove these oxidation products. This can be done if these acids are made to react with substances such as calcium carbonate or calcium oxide.
Decorative paints are paints used for coating buildings for decorative, functional and protective reasons. A high quality paint can incorporate up to 20% (w/w) of TiO2 (mainly rutile) and about the same amount of fillers, such as calcium carbonate or talk. TiO2 is used for give to the paint opacity and whiteness while filers are necessary for helping on the opacity and for lowering the price.
It seems then that paints can serve for controlling the NOx formed in cities, helping to control the air pollution. This is not the case because the TiO2 photoactivity promotes the degradation of the resin at the paint surface. The TiO2 used in paints is then treated with a very thin coating such as alumina and has no photoactivity.
NOx are essentially formed due to cars circulation. A polluted city can have NOx concentrations in the range of 310 µg/m3 (e.g. Prague in 1995). A recent study showed that 1 kg of TiO2/CaO (1:1) can treat about 5x106 m3 of air containing 0.06 ppm of NOx. Using buildings coating for treating the ambient air is a completely innovative and promising solution. The largest Portuguese paint company, CIN, uses each year about 1.5x106 kg of TiO2 for decorative exterior paints and have about 30% of the market. These data show that the produced paint is potentially able to photooxidise a significant fraction of the NOx produced in Portugal every year.
This project aims the development and study of paint additives for photocatalytic oxidation of NOx. It will be studied the photocatalytic activity of uncoated TiO2 (rutile), with 0.21 µm diameter (the one which gives the highest opacity), the most promising classes of resins and fillers (talks, calcium carbonate, etc.), and special aditives such as zeolites for improving the NOx adsorption and transport until the catalyst. A strategy for protecting the resin to be photodegraded will be also considered. |