Nano composite improves air quality

Materials World magazine
9 Dec 2019

A graphene-based photocatalyst lowers levels of atmospheric pollutants better than existing materials. Ceri Jones finds out how. 

A surface coating made of graphene and titania has been proven to break down nitrogen oxides in the air at a rate 70% higher than titania alone. 

The composite was developed by a collaborative team of partners, including researchers at the University of Cambridge’s Graphene Centre who produced the new material and Italcementi HeidelbergCement Group who tested it. 

The group decided to test the new composite material and the titania nanoparticle control against real pollutants, to assess the value for combatting urban air quality problems. 

Nitrogen oxides, mostly from industrial and vehicle emissions, are one of the main contributors to air pollution. 

It was already known that when exposed to sunlight, titania degrades nitrogen oxides and harmful organic compounds, breaking them down into benign products. 

Using this as a starting point, the team set out to make a photocatalytic coating material that would perform the same function and be practical to use. 

'We decided to couple graphene to the most-used photocatalyst, titania, to boost the photocatalytic action,’ said Italcementic Chemical Engineer, Marco Goisis. ‘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.’ 

Making it work 

Firstly, the Cambridge team produced graphene via liquid-phase exfoliation using water and atmospheric pressure, and carried out the process in the presence of titania nanoparticles. 

This was used to coat a range of materials, such as exterior building walls, where it proved to degrade pollutants when in sunlight, resulting in photodegradation matter which could be safely cleaned or washed away. 

To confirm the efficacy, the rate at which graphene-titania and lone titania could degrade nitrogen oxides was measured, reporting a 70% increase in the composite's performance. This was followed by testing the degradation of rhodamine B, it being a suitable marker to compare results for a range of volatile organic pollutants. 40% more rhodamine B was broken down by the composite, although this was performed in water and under UV irradiation. 

‘Coupling graphene to titania gave us excellent results in powder form – and it could be applied to different materials, of which concrete is a good example for the widespread use, helping us to achieve a healthier environment,’ Goisis said. 

‘It is low-maintenance and environmentally friendly, as it just requires the sun’s energy and no other input.’ 

University of Cambridge explained that ‘ultrafast transient absorption spectroscopy measurements revealed an electron transfer process from titania to the graphene flakes, decreasing the charge recombination rate and increasing the efficiency of reactive species photoproduction – meaning more pollutant molecules could be degraded’.

Research into anti-pollution coatings and practical environmental products is continuing at the University of Cambridge’s Cambridge Graphene Centre. 

Read more in the full paper, Photocatalytic activity of exfoliated graphite-TiO2 nanocomposites, published in Nanoscale, here:

Image: Concrete and glass buildings that could be coated with anti-pollution nanoparticle materials. Credit: Nate Steiner.