We live our lives surrounded by all sorts of smells, and there is a wide array of products designed to eliminate the more unpleasant ones. Paper is the latest material to be given deodorizing properties, and the anti-odorant papers developed by Japanese manufacturers have so far met with positive reviews. One such material is photocatalyst-coated paper, which was made public in 2006 by major paper maker Nippon Paper Industries Co.

A paper fan that cleans the air. (Product provided by Nippon Paper Industries)

The Science Behind Photocatalyst-Coated Paper
A photocatalyst is any substance that mediates chemical reactions and is activated by light energy. When organic matter in the atmosphere comes into contact with a photocatalyst, it is oxidized at an increased rate and breaks down into water and carbon dioxide. Any smell the matter gives off is thus eliminated, purifying the air.

The most common photocatalyst is titanium oxide, which is already used as an air purifier in things like construction materials and air conditioners. Photocatalytic paper, or paper containing titanium oxide, has been commercially available since before photocatalyst-coated paper was developed, but the titanium oxide in old-style photocatalytic paper is embedded in the paper's fibers, shading it from the ultraviolet light that it needs to mediate reactions. What is more, the oxidization-hastening effects of the titanium oxide degrade the paper itself. Nippon Paper Industries used what is known as an inorganic binder to overcome these setbacks.

How photocatalytic paper works. (C)Nippon Paper Industries

An inorganic binder is an inorganic substance with particles smaller even than titanium oxide. The binder is adhered to the surface of the titanium oxide, which can then be used to coat the surface of paper. This way the titanium oxide cannot easily degrade the paper because the binder prevents them from directly touching. It can still, however, come into contact with organic substances in the air through the small openings in the inorganic binder, enabling it to exhibit its air-purifying effects.

Advantages Over Other Deodorizers
Photocatalyst-coated paper is a strong anti-odorant because of this structure. Odors are emitted from organic substances, most of which have a main culprit chemical. For example, the smell of cigarettes is caused by acetaldehyde, sweat and pet smells mainly come from ammonia, while formaldehyde is said to be one of the causes of "sick house syndrome," which became a subject of concern when it began occuring in newly built residences. Tests by Nippon Paper Industries show that photocatalyst-coated paper virtually eliminates these three substances, and comparative tests for removing ammonia demonstrate that it strongly outperforms deodorizers on the market. Also, because deodorizers themselves adsorb the source of an odor to eliminate smell, they become saturated once they take in a certain amount. Titanium oxide, however, never changes in its role as a catalyst, and therefore exhibits semi-permanent air-purifying effects without becoming saturated.

Samples of products made using photocatalytic paper. (Products provided by Nippon Paper Industries)

In light of these advantages, Nippon Paper Industries is putting PCP to a variety of uses. It teamed up with the Yomiuri Shimbun newspaper in 2005 to produce a special advertisement supplement printed on photocatalytic newsprint. The use of this unique paper is spreading, with financial institutions, food companies, and other enterprises putting it in their calendars to drive home an image of cleanliness, and paper companies using it to make their tissue paper packaging.