How PECO-filters work

Photo ElectroChemical Oxidation (PECO) technology was developed over 20 years innovating air purification by destroying organic pollutants at the chemical level. After it has been activated by light inside the Molekule device, the surface of the catalyst can break down organic pollutants such as VOCs, viruses, bacteria, mold spores and allergens into harmless gases like carbon dioxide and water vapor.

Traditional air filtration captures pollutants by filtering contaminated air through a labyrinth of tiny fibers in the hope that only breathable air finds its way out the other side. Research has shown that this method is incomplete and additional methods such as source control may be required. Instead of trying to catch the pollutants in a jungle of small spaces, the fibers of PECO-filters are coated with a catalyst that performs a powerful chemical reaction that destroys organic pollutants at the smallest possible scale.

 

PECO is an oxidizing catalyst

The star of PECO-filter is the catalyst coated onto the fibers of the filter. When organic pollutants come into contact with the catalyst they are destroyed. There are some details and nuances to the destruction process that involve a little chemistry and physics.

The catalytic part of PECO refers to the creation of pollution-destroying hydroxyl radicals when it is exposed to light. These radicals essentially speed up what is known as oxidation, which is the O in PECO. 

Ordinarily, almost anything that comes into contact with the air we breathe is slowly oxidized by the oxygen in the atmosphere. Oxidation is a chemical reaction at the center of many different natural processes, including the decomposition of organic matter. A very fast and familiar form of oxidation is called combustion or burning. When something like wood burns, the chemicals that compose it are converted into gases that float away and little is left behind but a small pile of ash. When something is burned so hot that it incinerates, almost nothing is left behind at all.

 

PECO is activated by light

PECO is a photocatalyst, which is just a catalyst that is activated by light. Photocatalysts need strong sources of light to activate their destructive power, so most photocatalysts are activated by UV light. Certain types of high-energy UV can produce ozone, which is a toxic gas that also may be more dangerous than the pollutants the purifier is attempting to reduce.

The PECO catalyst was specially designed to reduce the widest array of pollutants possible compared to traditional solutions without introducing any extra toxins into the air, so PECO is designed to use safe UV-A light. UV-A light is most commonly found as the purplish light that is sold as “blacklight” and makes posters and other bright colors glow fluorescently. UV-A light is not known to produce ozone but still has the energy necessary to activate the PECO photocatalyst.

 

PECO is efficient photocatalytic destruction

The concept of exposing pollutants to a photocatalyst in order to destroy them is not new, but there are many substances that can be used as a photocatalyst and many ways to prepare them. Designing a catalyst that is efficient and effective is challenging and fraught with pitfalls. An inefficient catalyst can generate incompletely destroyed pollutants that may be more dangerous than their original forms. This is similar to combustion, where wood smoldering at a relatively low temperature will produce a lot of smoke, but wood that is incinerated at a high temperature will produce much less smoke, if any.

One of the primary reasons PECO is efficient is because it is coated onto the fibers of the filter. As pollutants try to find their way through the labyrinth of the filter, they encounter the catalyst which produces powerful chemicals known as hydroxyl radicals on its surface. Hydroxyl radicals are created from trace amounts of water in the air and are one of the most reactive substances known. They eagerly react with anything nearby, including not just pollutants but also molecules in the air. As a result they exist for just a fraction of a second before turning back into water molecules if there are no pollutants present.

One of the primary challenges in designing a photocatalytic air purifier is ensuring that enough hydroxyl radicals are available to destroy pollutants. Not only does the PECO photocatalyst create a large amount of hydroxyl radicals, but each fiber offers a huge surface area for pollutants to come into contact with. They are unlikely to find their way through the filter without passing through a cloud of destructive hydroxyl radicals.

 

Not everything can be destroyed by oxidation

Oxidizing contaminants is a great way to make them non-toxic. Bleach is a powerful oxidizing agent to use on surfaces that can kill pathogens or eliminate odors by oxidizing them. Fire also oxidizes pathogens and eliminates odors. But not all pollutants can be oxidized. In some cases oxidation does not neutralize their toxicity. For example, tiny particles of sand in the air are unhealthy to inhale, and the oxidation power of neither bleach nor fire would change that. Since PECO relies on oxidation to destroy pollutants, Molekule devices instead trap contaminants like particles of sand in their maze of filter fibers, just like a traditional non-photocatalytic filter.

What can be destroyed by oxidation are organic pollutants. Organic pollutants include particles made from living things, such as viruses, bacteria, mold spores, and allergens. Many chemicals known as VOCs, such as formaldehyde and benzene, are also organic since they were originally purified from fossil fuels. It is these pollutants that have been targeted by the development of PECO, and are rendered into trace elements of the atmosphere like carbon dioxide and water.

 

You can find evidence of how well Molekule air purifiers can destroy organic pollutants on our technology page, and can read the lab reports on our papers page

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