Dec 4 2019
Graphene Flagship has created a new graphene-titania photocatalyst that is capable of degrading around 70% more atmospheric nitrogen oxides (NOx) when compared to regular titania nanoparticles. This was discovered when performing tests on actual pollutants.
The photocatalyst degrades up to 70% more atmospheric nitrogen oxides (NOx) than standard titania nanoparticles in tests on real pollutants. Image Credit: Italcementi/Heidelberg Cement/Graphene Flagship.
Graphene Flagship has collaborated with Politecnico di Milano, the University of Bologna, NEST, CNR, the Israel Institute of Technology, Italcementi HeidelbergCement Group, the University of Cambridge, and the Eindhoven University of Technology for developing the photocatalyst.
Air pollution has become a growing concern, specifically in less developed countries and in urban areas. In fact, air pollution causes diseases that are responsible for one out of every nine deaths, as reported by the World Health Organization. This is mainly caused by organic pollutants like volatile compounds and nitrogen oxides, and these pollutants are largely discharged by industry and vehicle exhausts.
To deal with this issue, scientists are constantly looking for an innovative way to eliminate more amounts of pollutants from the air. Photocatalysts like titania offer an excellent way to achieve this.
Upon exposure to sunlight, titania degrades nitrogen oxides that are extremely harmful to human health and also degrades volatile organic compounds that exist at the surface. It then oxidizes both nitrogen oxides and volatile organic compounds into harmless or inert products.
At Graphene Flagship, the research team studying photocatalytic coatings has now created a unique graphene-titania composite that has considerably more powerful photodegradation characteristics when compared to bare titania. The research team was directed by Italcementi, HeidelbergCement Group, Italy.
We answered the Flagship’s call and decided to couple graphene to the most-used photocatalyst, titania, to boost the photocatalytic action. 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.
Marco Goisis, Research Coordinator, Italcementi
Liquid-phase exfoliation of graphite is a process that produces graphene. This process was carried out by the researchers using only atmospheric pressure and water in the presence of titania nanoparticles. The researchers eventually produced a novel graphene-titania nanocomposite that can be coated on the materials’ surface to passively eliminate pollutants from the atmosphere.
If this nanocomposite coating were applied on the walls of buildings or to concrete on the street, the innocuous photodegradation products would be manually cleaned off, or washed away by wind or rain.
In order to quantify the photodegradation effects, the researchers tested the novel photocatalyst against NOx and observed that the photocatalytic degradation of nitrogen oxides was considerably enhanced when compared to regular titania.
Rhodamine B was also used as a model for volatile organic pollutants, since its molecular structure is almost similar to that of the pollutants discharged by agriculture, industry, and vehicles. The researchers discovered that the graphene-titania composite degraded 40% more rhodamine B when compared to titania alone, 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. It is low-maintenance and environmentally friendly, as it just requires the sun’s energy and no other input,” added Goisis.
However, there are challenges that need to be tackled before this method can be utilized on a large scale. Nevertheless, approaches that are more economical are required for large-scale production of graphene. It is important to deepen the interactions between the host material and the catalyst, and studies have to be performed to investigate the photocatalyst’s long-term stability in the outdoor setting.
Furthermore, ultrafast transient absorption spectroscopy measurements demonstrated a process of electron transfer from titania to the graphene flakes. This increased the efficiency of the photoproduction of reactive species and decreased the rate of charge recombination—which means more pollutant molecules can be degraded.
Photocatalysis in a cementitious matrix, applied to buildings, could have a large effect to decrease air pollution by reducing NOx and enabling self-cleaning of the surfaces—the so-called ‘smog-eating’ effect.
Xinliang Feng, Work Package Leader, Functional Foams and Coatings, Graphene Flagship
Feng continued, “Graphene could help to improve the photocatalytic behaviour of catalysts like titania and enhance the mechanical properties of cement. In this publication, Graphene Flagship partners have prepared a graphene-titania composite via a one-step procedure to widen and improve the ground-breaking invention of ‘smog-eating’ cement.”
“The prepared composite showed enhanced photocatalytic activity, degrading up to 40% more pollutants than pristine titania in the model study, and up to 70% more NOx with a similar procedure. Moreover, the mechanism underlying this improvement was briefly studied using ultrafast transient absorption spectroscopy,” Feng further added.
Integrating graphene into titania to create a new nanocomposite was a success. The nanocomposite showed a strong improvement in the photocatalytic degradation of atmospheric NOx boosting the action of titania. This is a very significant result, and we look forward to the implementation of the photocatalytic nanocomposite for a better quality of air in the near future.
Enrico Borgarello, Global Product Innovation Director, Italcementi
Italcementi is part of the HeidelbergCement Group, one of the largest cement producers in the world.
But the reasons to integrate graphene into concrete do not end here. Italcementi is also exploring another product—an electrically conductive graphene concrete composite—displayed at Mobile World Congress in February 2019. When the composite is added as a layer in flooring, it can discharge heat upon passing an electrical current through it.
“You could heat your room, or the pavement, without using water from a tank or boiler. This opens the door to innovation for the smart cities of the future—particularly to self-sensing concrete,” added Goisis.
Such concrete would be able to detect strain or stress in concrete structures and track structural defects, and thus offer warning signals when the structural integrity of the concrete is close to failure.
Andrea C. Ferrari, Science and Technology Officer of the Graphene Flagship and Chair of its Management Panel, added, “An ever-increasing number of companies are now partners, or associate members of the Graphene Flagship, since they recognize the potential for new and improved technologies.”
“In this work, Italcementi, a leader in Italy in the field of building materials, demonstrated a clear application of graphene for the degradation of environment pollutants. This can not only have commercial benefits, but, most importantly, benefit of society by resulting in a cleaner and healthier environment,” concluded Ferrari.