Titanium dioxide nanoparticles: the walls are white but dangerous

You can not stop progress. This is probably the case in construction and
the invention, now in use, of self-cleaning walls with dioxide nanoparticles of titanium. The walls remain white but the environment and health are pale on sight of eye.

Paris is the city of light and wants to remain so. To do this, nothing better than to have the walls of the buildings of a perpetually immaculate white. Impossible due to pollution, vehicle exhaust, mold do you think? If that was true yesterday, it is no longer true today. This feat comes from progress in the building materials that are now used, as in the 17th arrondissement of the capital where a whole district of 74 homes and shops will be built with revolutionary walls, stuffed with nanoparticles of titanium dioxide.

At the origin of this innovation, a problem encountered by all buildings, the walls darken over time. The dirt that inevitably darkens the facades is the result of insufficient power of the sun’s UV to degrade all the micro-organisms that develop there. The principle of self-cleaning concrete is simple: increase the effectiveness of UV in a sustainable way so that they can destroy all these micro-organisms. For this, a specific catalyst is put in the concrete: a titanium oxide. This catalyst acts as a UV amplifier and does not degrade over time, maintaining its efficiency without wear.

Unparalleled properties

Titanium dioxide indeed has two photocatalytic and hydrophilic properties which have aroused intense scientific, commercial and financial interest. What savings when you no longer need to restore the facades.

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Photocatalysis is a chemical reaction that occurs naturally in the environment but, without a process accelerator, it proceeds very slowly. The photocatalysis process destroys volatile organic compounds (VOCs), particles and ozone, but also eliminates microorganisms such as bacteria, viruses, moulds, fungi, moss or algae. These properties have been known for at least ten years and have been the subject of numerous industrial developments.

The hydrophilic properties of titanium dioxide allow water to form a continuous film, rather than droplets, on a material treated with this substance. This effect in particular prevents the formation of fog and has the consequence that the water runs off evenly. Dirt, which normally sticks to the wall when the water evaporates, is then removed with the liquid. Molds, decomposed by photocatalysis, cannot attach themselves. These properties, at the origin of the self-cleaning virtues of titanium dioxide walls, make them all their interest for new constructions.

But the picture is not all white

The only major problem with this innovation: the environmental and health consequences, because the walls are not neutral from this point of view. The degradation of nitrogen oxides, from vehicle engines, produces nitrates. A good part of these substances is eliminated with rainwater and ends up in waterways. While nitrogen oxides are air pollutants, nitrates pollute water since they promote the growth of aquatic plants in rivers. One thinks of the problem of green algae in Brittany due to nitrates from agriculture. When will the Seine, the Loire and the Rhône be saturated by algae?

The environment, but also health, on March 10, 2006, the International Agency for Research on Cancer (IARC) classified titanium dioxide as possible carcinogen for humans (category 2 B). In rats exposed to titanium dioxide, a long-term pulmonary toxicological impact was observed, with “saturation of pulmonary clearance accompanied by chronic pulmonary inflammation, production of reactive oxygen species, decrease in defense mechanisms (antioxidants), cell damage, cell proliferation and fibrosis. In vitro tests show cell toxicity of the inflammatory type (oxidative stress).

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Another major drawback, the chemical reactions take place on the surface of the walls, in order to increase the efficiency of the walls, it is therefore important that the particles are as high as possible. For this reason, this substance is used in the form of nanometric particles (with a diameter of less than 100 nm). Unlike its crystalline form, titanium dioxide nanoparticles pose health risks, in particular due to their very small size and the reactivity of the atoms found on the surface of the particles, the main function of which is the oxidation of organisms. living.

The Swiss don’t want it

In Switzerland, a report published jointly by the Federal Office for the Environment (FOEN) and the Federal Office for Public Health (OFSP) highlights the lack of knowledge concerning the potential risks of synthetic nanoparticles in general. The two offices have thus launched a research and development action plan concerning nanoparticles. The Grand Council of the Republic and Canton of Geneva did not wait for the results of the risk studies. He simply banned the use of this new self-cleaning material for the construction of any new building.


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