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All You Need to Know About Photocatalytic Oxidation for Air Sterilisation July 2, 2020





“Photo-what you say?”

“Photocatalytic oxidation.”

Phew.  What a mouthful.

I struggled just trying to sound it out. The verbal challenge inspired me to research this advanced sterilisation technology.
I am no science doctorate, and I know not all of you are either. I wrote this article to help you and I understand the basic science involved in the photocatalytic oxidation (PCO) process.



Before we start, here is a quick glossary of words you need to understand in this article:


  • Catalyst: a catalyst is something that increases the rate of a chemical reaction without changing itself.
  • Photo-catalyst: a photo-catalyst uses light radiation to increase the rate of reaction.
  • Oxidisers: an oxidiser is an electron-accepting reactant, meaning it can damage the DNA of a molecule.



How does photocatalytic oxidation work?

This process has 5 key elements:


1. Radiation

Ultraviolet (UV) light, from fluorescent lamps or natural sunlight, is directed at a catalyst.


2. Catalyst

Titanium dioxide (TiO2) is the photo-catalyst. The photo-catalyst absorbs the UV radiation and creates a reaction.


3. Reaction

The reaction between UV radiation and TiO2 forms hydroxyl radicals (OH).  Hydroxyl radicals are more aggressive and powerful oxidisers than chlorine, ozone, and peroxide.

These extremely powerful oxidisers last for billionths of a second, in which time they neutralise air pollutants. The life of ·OH is so short they ‘defy measurement by precision laboratory techniques’¹.  This means the oxidation occurs on the surface of the catalyst, as the oxidants die before they travel away from it. 


4. Neutralisation

The hydroxyl radicals destroy the cellular structure, intracellular mass and DNA/HNA chromosomes² of the air pollutants, causing them to decompose.


5. By-product

Once the pollutants decompose, they convert to harmless water (H20) and carbon dioxide (CO2).


Simply put, UV light and titanium dioxide create an extremely powerful reaction that neutralises air pollutants and converts them to water and CO2.


What pollutants can photocatalytic oxidation kill?

Not all PCO systems are equal; the effectiveness of the process depends significantly on the system design. There are many factors involved in this (see later in the article), however, a well-designed, properly functioning PCO air purifier should neutralise or inactivate the following pollutants:

  • VOC’s – Volatile organic compounds
  • CAC’s – Chemically active compounds
  • bacteria
  • virus
  • mould
  • fungi
  • toxins
  • pollen, and
  • other allergens.

PCO can destroy particles as small as 0.001 microns (nanometre).

If that sounds like just another number or piece of data, try to think about it in terms of hair.  A human hair is approximately 75 microns in diameter – 0.001 microns is 75,000 times smaller than an average human hair!


Where is photocatalytic oxidation used?

Photocatalytic oxidation was originally achieved in 1972 by scientists who discovered photocatalysis as an electrode in water.³

Photocatalytic oxidation is now mainly used to treat water and air.  Because it can decompose pollutants and enhance the quality of both air and water, it is a suitable way to treat indoor air and potable water.


What should I watch out for when buying a PCO air cleaning unit?

There are several factors that can reduce the efficiency of PCO and even result in it producing harmful by-products. Before you invest in a PCO system to treat your air, you need to carefully consider these questions:


> Are the UV lamps certified ozone-free for their entire recommended lifespan?

Ozone is hazardous to humans (especially the respiratory system). Some UV lamps, especially old ones, can generate Ozone.


> Are any by-products produced?

Some PCO systems produce hazardous by-products due to ineffective reactions. If incomplete oxidation occurs, it can produce hazardous by-products , like formaldehyde. Incomplete oxidation can occur when the PCO process contains unsuitable low-pressure mercury lamps. Make sure you check that the system guarantees that it releases no by-products.


> Is the system designed to treat all the air in a single air pass?

The system needs to expose all incoming air to the photocatalytic oxidation before expelling it again. If it isnt, it it will not be able to neutralise the pollutants in a single air pass. This is vital, as you don’t want to be spreading the remaining contaminants around the room. OH molecules only remain active for billionths of a second. Thus, they do not travel though air away from the catalyst (titanium dioxide surface). All the action must happen as the air touches the surface. This is why it is critical that the sterilisation chamber allows enough reactions occur to treat all the air in one single air pass.


In summary 

A well-designed air purification system that uses photocatalytic oxidation will be extremely effective at eliminating pollutants from the air. Radic8’s Viruskiller technology incorporates photocatalytic oxidation to remove 99.9999% of virus, bacteria and toxins from the air. Got a question about this? Ask below. 


Denver Prestidge, business development manager

About the Author:

Denver Prestidge is a fresh Industrial Hygiene and Air Quality apprentice for Presco Environmental.

Focused on sourcing and developing innovative, industry leading products for New Zealand’s food producers, Denver is always looking for ways to challenge and improve the status quo.

If you would like to get in touch with Denver, feel free to reach out at any time – denver@presco.co.nz.


¹ Photo Catalytic Oxidation or PCO Technology for Improving Air Quality – HVAC Performance Products, Inc.

² Photocatalytic Oxidation (PCO) – Hamilton Thorne

³ Fujishima – Science Direct



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