All about photocatalysis

Photocatalysis can be found in a variety of domains, including the treatment of air, water, and in applications within the industrial world. It is a highly effective method of removing airborne pollutants from our breathing air, especially volatile organic compounds (VOCs). What, exactly, is photocatalysis? How does it work? Read on to learn more.

What is photocatalysis?

Photocatalysis, also called photocatalytic degradation, is quite simply a chemical reaction accelerated by light. Etymology tells us that ‘photo’ means ‘light’, and ‘catalysis’ means ‘dissolution’. A catalyst causes or speeds a chemical reaction.

Photocatalysis in principle

Photocatalysis is a simple redox (reduction-oxidation) reaction that involves the activation of a semiconductor (titanium oxide, or TiO2, the catalyst) by light (UV rays). It is the decomposition and the degradation of pollutants through the use of light rays on the surface of a catalyst (photocatalyst, more specifically). The process results in water and carbon dioxide.

Photocatalysis in practice: does it work in an air purifier?

An air purification device that contains photocatalysis technologies employs photocatalytic oxidation technology to purify indoor air.

Located in the centre of an air purifier are the rays of the UV lamp. These rays then strike the internal layer of the multi-layer filter which is made of TiO2, a photocatalyst.

When TiO2 and UV light combine, a reaction takes place between the oxygen and water present in the air, generating free radicals (also called 'active oxygen'). These free radicals are highly depolluting and destroy airborne pollutants. This process is useful against all types of pollutants but is particularly useful against VOCs. The purified air is then recirculated back into the room.

Here is a more technical explanation for the chemistry buffs:

• TiO2, a catalyst, releases electrons when it is energised by the UV rays.
• These electrons interact with water molecules (H20) present in the air.
• The water molecules then break up into hydroxyl radicals (OH).
• The hydroxyl radicals then attack bigger organic (carbon-based) pollutants which breaks apart their chemical bonds, converting them into a harmless substance (like CO2 and water)².

Professionals tend to tread lightly when talking about them because free radicals have a bad connotation, often evoking fear. Free radicals naturally present in the air can damage the skin, which is why health experts recommend that we consume foods containing antioxidants: these molecules fight to protect us from this damage. However, it is precisely the strong reactivity of these molecules that also allows them to fight atmospheric pollution so effectively. Fortunately, in the case of photocatalysis, everything happens inside the device, keeping us perfectly safe from any harm.

In the absence of chemical pollution, free radicals will simply recombine. Their high reactivity with surrounding molecules ensures a very short lifespan. The scheme below shows the photocatalysis process in a bit more detail (with TiO2 as the catalyst, or photocatalyst more specifically, in this case).

Source ¹

Which types of pollution are targeted by photocatalysis?

A pollution control technology, photocatalysis is not a type of filtration. It is a reaction, rather, that is particularly effective against chemical pollution and gaseous pollutants, commonly called VOCs. While VOCs can be found in nature, they are more often than not of human origin and are dangerous. A common output of industrial activities, VOCs are linked to products like solvents, cleaning agents, sprays, cosmetic products, and paint.

Some of the most notable VOCs that are removed by photocatalysis are nitrogen oxides, carbon dioxide (CO2), carbon monoxide (CO), formaldehyde, ethanol, butane, toluene, benzene, and acetone.

Recent scientific studies have presented findings that demonstrate the effectiveness of photocatalysis in combatting airborne pollutants:

• Photocatalysis, even when used at low intensity with the use of TiO2 as a photocatalyst, achieves reduction of influenza viral strength and spread³
• With the use of TiO2 films, photocatalytic technologies help speed up the decomposition of E. coli bacteria and the Herpes simplex virus, amongst other organic matter⁴
• Photocatalysis has been declared an ‘eco-friendly depollution method that mimics nature’s process and has great potential to be developed as a key technology for air purification and air pollution degradation’^5,7
• With the need to find solutions for the dangers of air pollution on human health, the future is promising for using photocatalysis as a method for photodegradation of chemical contaminants and photodisinfection of pathogens⁶

The benefits of the Eoleaf photocatalysis technology

Photocatalysis serves as an effective method of removing airborne pollutants in any setting, individual households and office buildings alike. Photocatalysis does not require the use of any chemicals or external energy, only needing the light of the integrated UV lamp and a catalyst.

Individual settings

What makes photocatalysis so interesting as a depollution technology is that it does not simply trap pollutants, like a filter does. When a filter traps pollutants, they do not simply disappear: they still need to be destroyed somehow!

Photocatalysis completely transforms dangerous chemical pollutants into substances that cannot harm us. They are then eradicated or destroyed entirely².

Photocatalysis can notably fight against VOCs, mould and its spores, and germs (bacteria and viruses) suspended in the air.

Professional settings

In an office environment, clean air can provide a handful of benefits.

High-quality air purifiers containing photocatalytic air filters can drastically improve air quality. They destroy air pollution particles that can lead to illness amongst workers (including viruses like COVID-19 and its variants). This can reduce the need for employees to take sick leave and increase productivity.

Poor indoor air quality can lead to uncomfortable and distracting symptoms like headaches, dizziness, and difficulty breathing. It can also aggravate existing conditions, especially asthma (triggering asthma attacks), chronic obstructive pulmonary disease (COPD), and heart disease. Indoor air pollution also leads to worsened allergy symptoms, fatigue, and impacts mental health.

The Eoleaf difference

When photocatalysis technologies are combined with other technologies in one device, it creates a device that is capable of combatting all air pollutants found in our indoor air. This is why Eoleaf’s products come equipped with a proprietary filter containing 8 different filtration technologies that work together to offer you the best air filtration capabilities on today’s market.

Our devices allow you to fight against VOCs and chemical pollution, biological pollution, allergens, germs, and fine particle pollution (particulate matter or PM). Our air purifiers can also combat unpleasant odours in your home or office space due to our activated carbon filters!

Our photocatalysis technology does not emit any ozone. In fact, photocatalysis makes it possible to destroy the ozone present in the air and to even prevent the formation of ozone by degrading its precursors (oxides and other gases).

Resources

¹ Samson, I. (n.d.). Integration of biomimetic principles as a tool for sustainable building design in shopping mall in Lagos State. Federal University of Technology Minna. https://www.researchgate.net/publication/339281465_INTEGRATION_OF_BIOMIMETIC_PRINCIPLES_AS_A_TOOL_FOR_SUSTAINABLE_BUILDING_DESIGN_IN_SHOPPING_MALL_IN_LAGOS_STATE 

² Woodford, C. (2022, September 5). How do photocatalytic air purifiers work?. Explain that Stuff. https://www.explainthatstuff.com/how-photocatalytic-air-purifiers-work.html 

³ Nakano R, Ishiguro H, Yao Y, Kajioka J, Fujishima A, Sunada K, Minoshima M, Hashimoto K, Kubota Y. Photocatalytic inactivation of influenza virus by titanium dioxide thin film. Photochem Photobiol Sci. 2012 Aug;11(8):1293-8. doi: 10.1039/c2pp05414k. Epub 2012 May 14. PMID: 22580561.

⁴ Hajkova, P., Spatenka, P., Horsky, J., Horska, I., & Kolouch, A. (2007). Photocatalytic effect of tio2 films on viruses and bacteria. Plasma Processes and Polymers, 4(S1). https://onlinelibrary.wiley.com/doi/abs/10.1002/ppap.200731007 

⁵ He, F., Jeon, W. & Choi, W. Photocatalytic air purification mimicking the self-cleaning process of the atmosphere. Nat Commun 12, 2528 (2021). https://www.nature.com/articles/s41467-021-22839-0 

⁶ Ren, H., Koshy, P., Chen, W.-F., Qi, S., & Sorrell, C. C. (2017a). Photocatalytic materials and technologies for Air Purification. Journal of Hazardous Materials, 325, 340–366. https://www.sciencedirect.com/science/article/abs/pii/S0304389416307968?via%3Dihub 

⁷ Sharma, S., Kumar, R., Raizada, P., Ahamad, T., Alshehri, S. M., Nguyen, V.-H., Thakur, S., Nguyen, C. C., Kim, S. Y., Le, Q. V., & Singh, P. (2022). An overview on recent progress in photocatalytic air purification: Metal-based and metal-free photocatalysis. Environmental Research, 214, 113995. https://www.sciencedirect.com/science/article/abs/pii/S0013935122013226