Active Coatings to Improve Air Quality

Air pollution is one of the main problems of the 21st century, both for the environmental damage it causes and its impact on human health. Air pollution is defined as the presence of compounds in the air that cause a serious nuisance, risk, or damage to the safety or health of people and the environment.

Active coatings can significantly contribute to improving air quality by reducing the presence of air pollutants. Reducing these pollutants is essential to protect public health and the environment.

Air Pollutants

The primary impact of air pollutants on people are respiratory and pulmonary problems. The International Agency for Research on Cancer (IARC) has classified air pollutants in Group 1 as causing lung cancer in humans. Additionally, these pollutants contribute to the formation of smog and ozone, major drivers of the greenhouse effect and the depletion of the ozone layer.

Sources of Pollutant Emissions

When considering sources of pollutant emissions, transportation and industry often come to mind. However, other sources, such as cleaning products, paints, and various chemical-containing products, also contribute. High concentrations of these pollutants can remain in the air long after the activity that produced the emission has ceased.

Consequently, air pollution occurs both outdoors and indoors. Studies by the United States Environmental Protection Agency (US EPA) revealed that levels of some common organic pollutants were 2 to 5 times higher inside homes than outdoors, regardless of whether the homes were located in rural or highly industrialised areas. Furthermore, pollutants travel with airflows, meaning outdoor contaminants enter homes, and vice versa.

Major Air Pollutants

The primary air pollutants include:

• Nitrogen oxides (NOx): Exposure to NOx can irritate airways and exacerbate respiratory illnesses.
• Suspended particulate matter (PM): Microparticles composed of sulphates, nitrates, ammonia, sodium chloride, carbonaceous particles (such as black carbon), mineral dust, and soot. These can cause cardiovascular, cerebrovascular, and respiratory impacts.
• Volatile organic compounds (VOCs): Common VOCs include benzene, toluene, and xylene outdoors, and formaldehyde indoors. These can lead to severe health problems in both the short and long term.
• Carbon monoxide (CO): Exposure to CO can cause breathing difficulties, fatigue, dizziness, and flu-like symptoms. High-level exposure can be fatal.
• Sulphur dioxide (SO2): Associated with asthma.
• Ozone (O3): A major component of smog. Ozone is formed from VOCs, CO, and NOx. Excessive ozone exposure can cause lung diseases.

Data indicates that nearly the entire global population breathes air exceeding the pollutant limits set by the World Health Organisation (WHO). On the same trajectory, these effects are expected to become even more critical in the future due to continued population growth.

Improving Air Quality with Active Coatings

Incorporating Photocatalytic Additives into Coatings

Certain solid materials, known as photocatalysts, can significantly reduce the presence of air pollutants by adsorbing and transforming them into less toxic compounds. These materials require only a light source to activate them, with sunlight being a highly advantageous option. Such materials can reduce a wide range of pollutants and are not consumed when acting on air pollutants, so they can act for long periods of time.

Photocatalysts act on organic compounds, allowing them to eliminate chemical substances that cause odours, act as biocides by reducing mould and bacteria, and even function as self-cleaning materials by removing organic compounds that discolour surfaces. Notably, these materials are cost-effective and safe for both humans and the environment.

Among the different applications of these materials, incorporating photocatalytic additives into coatings enables these materials to reduce air pollutants effectively.

How Do Active Coatings Work?

Active coatings can be applied to various materials, such as pavements, paints, facades, roofs, fabrics, wood, polymeric surfaces, or glass. Therefore, active coatings can be used in both indoor and outdoor products, enhancing air quality wherever they are in contact.

Depending on the final application and the material  on which the coating is to be applied, the coating formulation varies but always contains photocatalytic additives. The development of these active coatings aims to preserve the original properties of the product, including its physical appearance, to maintain its design. Another crucial aspect is the adherence of the active coating to the surface, ensuring long-lasting activity and adhesion.

The mechanism of active coatings is as follows:

1. The air pollutant comes into contact with the surface, where photocatalysts are activated by sunlight or UVA light.
2. These photocatalysts transform pollutants into less toxic compounds.
3. The less toxic compounds are removed from the surface by wind, rainwater, or similar processes.

These coatings oxidise all organic compounds they contact without selectivity. This feature improves air quality in diverse environments. Additionally, they maintain surfaces free from mould, bacteria, and organic dirt while reducing odours.

Key Benefits

• High pollutant removal efficiency: Photocatalytic coatings have been shown to significantly reduce concentrations of VOCs and NOx, enhancing air quality.
• Versatile applications: Photocatalytic additives can be incorporated into various coatings, enabling their use on a wide range of surfaces. Their non-selectivity towards organic compounds makes them effective for purifying different atmospheres.

Applications of Active Coatings

Transport

Active coatings can be applied to pavements, improving air quality significantly. Pavements include both pedestrian walkways and roads, with applications in materials like cement, paints, concrete pieces, or ceramics (e.g., tiles or paving stones). This use is gaining interest among public administrations and private entities, such as hospitals, architectural firms, and schools.

Building Construction

In construction, these coatings are mainly used on building facades due to their large surface area exposed to sunlight. They can be applied using ceramic coatings, cement panels, waterproof roofing, or paints that act as active coatings. Applications on vitrified steel coatings offer versatile uses for both indoor and outdoor purposes.

Indoor Spaces

Active coatings are valuable for hotels, shops, educational institutions, or healthcare centres. They are commonly applied via paints or tiles but can also be integrated into glass or curtain fabrics. In indoor applications, their ability to reduce odours from tobacco, kitchens, or waste is particularly beneficial. For schools and healthcare facilities, their ability to combat mould, bacteria, and viruses is especially important. Ensuring adequate sunlight or using UVA light sources is critical for activating these coatings.

La contaminación atmosférica es uno de los principales problemas del sigo XXI, tanto por el daño medioambiental que conlleva como el daño para las personas. La contaminación atmosférica se define como la presencia de compuestos en el aire que implican una molestia grave, riesgo o daño para la seguridad o la salud de las personas y el medio ambiente.

Los recubrimientos activos pueden contribuir de manera significativa a mejorar la calidad del aire al reducir la presencia de los contaminantes atmosféricos. La reducción de dichos contaminantes es clave para proteger la salud pública de la sociedad y la salud medioambiental.