Is this the future for atmospheric NOx removal?

Jon Lawson

An international group of scientists, including from the University of Cambridge, have developed a graphene composite that can ‘eat’ common atmospheric pollutants, and could be used as a coating on pavements or buildings.

This work has demonstrated a clear application of graphene for the degradation of environmental pollutants. This can not only have commercial benefits but, more importantly, a cleaner and healthier environment.

Working in collaboration with the Italcementi HeidelbergCement Group and other partners, the Cambridge scientists developed a photocatalyst that degrades up to 70 per cent more atmospheric nitrogen oxides (NOx) than standard titania nanoparticles in tests on real pollutants.

Atmospheric pollution is a growing problem, particularly in urban areas and in developing countries. According to the World Health Organisation, one out of every nine deaths worldwide can be attributed to diseases caused by air pollution. Organic pollutants, such as nitrogen oxides and volatile compounds, are the main cause of this, and they are mostly emitted by vehicle exhausts and industry.

While researchers are developing new technologies and energy sources that will drastically reduce the volume of pollutants emitted into the atmosphere in the first place, they are also on the hunt for new ways to remove more pollutants from the atmosphere. Photocatalysts such as titania are one way to do this. When titania is exposed to sunlight, it degrades harmful nitrogen oxides and volatile organic compounds present at the surface, oxidising them into inert or harmless products.

Researchers from the Cambridge Graphene Centre prepared and tested the composite, confirming its ability to photocatalytically degrade pollutant molecules, then researchers at Italcementi applied the coating to concrete to investigate its potential for environmental remediation.

“We decided to couple graphene to the most-used photocatalyst, titania, to boost the photocatalytic action,” said Marco Goisis from Italcementi. “Photocatalysis is one of the most powerful ways we have to depollute the environment because the process does not consume the photocatalysts. It is a reaction activated by solar light.”

By performing liquid-phase exfoliation of graphite – a process that creates graphene – in the presence of titania nanoparticles, using only water and atmospheric pressure, the scientists created the new graphene-titania nanocomposite.

They found that it passively removes pollutants from the air when coated on the surface of materials. If applied to concrete on the street or the walls of buildings, the harmless photodegradation products could be washed away by rain or wind, or manually cleaned off.