Graphene breeze: New technologies to fight air pollution

Air pollution is the biggest environmental risk to human health, according to the WHO, killing seven million people worldwide each year. Therefore, the European Commission has set a target of reducing premature deaths caused by air pollution by half before 2030. Linked to the pursuit of this goal, researchers at the Graphene Flagship are exploring the potential of graphene in applications like sensors, coatings and foams.

The term air pollution means the alteration of the indoor or outdoor environment by chemical, physical or biological contaminants. Typical sources include petrol and diesel vehicles, industrial plants and fires. The most common pollutants of concern include gases like carbon monoxide, nitrogen oxides (or NOX) and sulfur dioxide, as well as particulate matter. Air pollution is damaging to both the environment and public health, increasing the number of fatalities due to stroke, heart disease, chronic obstructive pulmonary disease, lung cancer and acute respiratory infections.

Despite much progress in reducing air pollution over the last 30 years, levels in some parts of Europe remain unacceptably high, with over 350,000 premature deaths caused by air pollution in 2021 – that’s almost 10% of overall deaths. Around 90 per cent of European city dwellers are exposed to harmful levels of air pollution, and with Europe’s urban population growing and ageing —therefore becoming more sensitive to air pollution — this threat to public health is only going to become more urgent.

Governments and organisations around the world are making tackling air pollution their top priority. As well as European targets, several of the United Nations’ sustainable development goals (SDGs) specifically address this issue, for example substantially reducing the number of deaths and illnesses from air pollution, or reducing the environmental impact of cities by improving air quality.

At the Graphene Flagship, research is underway to utilise the properties of graphene and layered materials in a new generation of sensors, foams and coatings that can all contribute to either monitoring air-quality or helping to improve it.

Monitoring air quality with graphene

Air quality can change dramatically even within small areas, for example one street may be within safe levels, while the next dramatically exceeds them. To help governments improve air quality within a particular city, accurate pollution mapping is needed — after all, understanding a problem is the first step towards solving it. One option is small, cost-effective sensors that could be installed around the city and provide real-time data. These sensors could even be integrated into mobile devices or wearables, informing individuals and enabling them to make personal decisions when it comes to air pollution, such as changing walking routes or wearing a mask if needed.

As part of the Graphene Flagship, researchers have developed this kind of air quality sensor, which utilizes the properties of graphene to create compact, low-energy sensors able to detect nitrogen dioxide in real time. The project is a collaboration between Graphene Flagship Partners at the National Physical Laboratory, UK, and Chalmers University of Technology, Sweden, alongside colleagues at the Advanced Institute of Technology, UK, Royal Holloway University, UK, and Linköping University, Sweden.

Nitrogen dioxide gas, produced by burning fossil fuels, causes airway inflammation which can lead to breathing problems and asthma attacks. Research even links exposure to nitrogen dioxide, and other NOX, to childhood obesity and dementia. Usually, air pollution is monitored using chemiluminescence, requiring large and expensive lab equipment, and metal oxide detectors, which lack sensitivity. By contrast, this new graphene-based sensor is both small and accurate, reporting pollutant levels based on changes in its electrical resistance.

When nitrogen dioxide from the air is absorbed by the graphene layer within the sensor, electrons are withdrawn from the graphene changing its resistance changes. This produces a recordable signal, using very simple electronics. The device’s simplicity means that small, commercially available sensors can easily be adapted and upgraded, using graphene-enabled sensors.

Smog no more

Graphene isn’t just useful to help us better understand air pollution in our towns and cities, it can help us reduce it too. Photocatalysts, such as titania, degrade nitrogen oxides when exposed to sunlight, oxidising them into inert or harmless products. As the reaction is activated by solar light, it neither consumes the photocatalyst or requires an additional power source, making it an effective way to depollute the environment. These photocatalysts can be applied to the surfaces of buildings and thereby decrease the amount of nitrogen oxides in the air, as well as resulting in a self-cleaning, smog-eating coating.

Graphene Flagship researchers, coordinated by Italcementi, of HeidelbergCement Group, Italy, have developed a graphene-titania composite that’s much more powerful than titania alone. By performing liquid-phase exfoliation to create graphene in the presence of titania nanoparticles — using only water and atmospheric pressure — the team created a new graphene-titania nanocomposite that when applied as a coating can passively remove pollutants from the air. The graphene titania composite was found to be 40 per cent more effective than titania alone, and in powder form can be applied to different materials, including concrete.

Air pollution is one of the biggest threats to public health faced by Europe. But, as with any problem facing society, research and innovation may hold an answer. Graphene technologies like compact NO₂ sensors or photocatalysts either fill a gap in the market or make an existing product much more effective.  Fully commercialising these technologies represents an exciting step towards making urban environments cleaner and safer for their inhabitants.