Light has amazing powers. It can give life to plants as they prepare their food using sunlight.

Not many people know that light can also purify the air we breathe. Some of the latest air conditioners and air purifiers use this characteristic of light to purify the air.

The photocatalytic filter is a prime example where ultraviolet light acts as the prime ingredient to clean the air of impurities with the help of a catalyst, titanium dioxide.

Photocatalytic filter – The Principle and its working

In straightforward terms, ultraviolet light shines onto a catalyst, titanium dioxide thereby breaking up the water molecules in the air to combine with the impurities and oxidise it.

Let us look at the working of the photocatalytic filter in brief.

In this filter, rays of ultraviolet light shine on a thin film of titanium dioxide to release electrons. These electrons interact with the water molecules (H2O) present in the air to form highly reactive hydroxyl ions (OH-).

These hydroxyl ions combine with carbon present in the organic pollutants and convert them into Carbon dioxide (CO2) and water. Hence, you can say this is a classic example of oxidation.

Therefore, this method of purification of air is also known as Photocatalytic Oxidation (PCO).

What is the role of titanium dioxide?

Titanium dioxide performs the role of a catalyst whereby it quickens the reaction without taking part in it directly. Therefore, this technology does not require titanium dioxide in large quantities. A thin film of the compound is enough to cover the surface of the substrate.

Photocatalytic filters – Pros

  • These filters do not trap the pollutants in their original form. They convert the harmful organic contaminants into carbon dioxide and water thereby completely transforming the toxic chemicals. In fact, they eradicate the pollutants.
  • The ultraviolet radiation has more energy than the standard light, and it is not visible to the human eye. It can produce the right amount of energy required to excite the titanium dioxide molecules to enable the release of electrons to start the oxidation process.

Photocatalytic filters – Cons

  • Exposure to ultraviolet light can give you sunburn as these light molecules have higher energy levels.
  • One of the by-products of the reaction is Ozone (O3), a dangerous air pollutant. It is a chemical variant of oxygen that can prove toxic if inhaled in large quantities. However, the air purifier manufacturers claim that these filters produce ozone much less than the guideline limit (0.05 parts per million).
  • This chemical reaction takes place on the surface of the titanium dioxide catalyst. Hence, there is a need to eliminate the polluted air from the surface using fans. These fans suck out the polluted air containing carbon dioxide and blow out clean air from the other end. Hence, it can take about half an hour for these filters to purify a large room.

Photocatalytic Filters – Use in air purifiers and air conditioners

These filters are handy as an additional appliance to the existing HEPA filters and other filters used in the air purifiers and air conditioners. The latest models of Daikin air conditioners make use of this technology to supplement their other filtration methods.

Source: Wikipedia, explainthatstuff

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