Foundation Prepped for Smog-Eating Concrete
A group of engineers at Graphene Flagship recently combined graphene and titanium dioxide nanoparticles to create a new photocatalyst that is reported to successfully remove pollutants from the air.
The research has since been published in Nanoscale.
Graphene Composite Research
According to the World Health Organization, outdoor air pollution can be linked to 3 million deaths a year. While major sources of air pollution are linked to inefficient modes of transport, household fuel and waste burning, coal-fired power plants, and industrial activities, not all air pollution originates from human activity, and can even be influenced by dust storms.
In an attempt to find new ways to remove more pollutants from the atmosphere, a research team at Graphene Flagship looked at titania in its photocatalytic coatings. (Titania is a common photocatalyst because when it’s exposed to sunlight, it degrades nitrogen oxides (NOx) and volatile organic compounds present at the surface, oxidizing them into inert or harmless products.) The work was coordinated by Italcementi, HeidelbergCement Group (Italy).
From the research, Graphene Flagship found that by performing a liquid-phase exfoliation of graphite in the presence of titania nanoparticles, a graphene-titania composite was created and when tested, degraded up to 70% more atmospheric nitrogen oxides than standard titania nanoparticles.
Reports also indicate that the composite can be applied as a coating to surfaces like streets, sidewalks or the walls of buildings, where its powered completely by sunlight. The photodegradation products, which are produced as a result, can be washed away by rain, wind or manually cleaned off.
In further testing, the team built photocatalytic panels and exposed them to pollutants. In one instance, the team used rhodamine B—which is similar to volatile organic pollutants when it comes to molecular structure—and found that when tested in water and activated by UV light, the graphene-titania composite degraded 40% more than a catalyst using only titania.
"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,” says Xinliang Feng, of Graphene Flagship. “Graphene could help to improve the photocatalytic behavior of catalysts like titania and enhance the mechanical properties of cement.”
Although the testing shows much promise, the team reports that more research is still needed before the technology could be commercialized.
Work for the project was conducted by engineers from the Graphene Flagship, the University of Bologna, Politecnico di Milano, CNR, NEST, Italcementi HeidelbergCement Group, the Israel Institute of Technology, Eindhoven University of Technology and the University of Cambridge.
Back in 2013, researchers at the Fraunhofer Institute for Molecular Biology and Applied Ecology IME in Schmallenberg, Germany, examined the effectiveness of photo-catalytic coatings at removing nitrogen oxides. During the research, samples were coated with titanium dioxide (TiO2), which acted as a catalyst in the presence of sunlight, breaking down the NOx into nitrate.
Later that same year, however, researchers from Indiana University in Bloomington, Indiana, found that TiO2-containing coatings—seen as promising for its role in breaking down airborne pollutants on contact—were likely, in real-world conditions, to convert abundant ammonia to nitrogen oxide.
The team noted that its research was timely, as the Environmental Protection Agency was developing stricter regulations for ground-level ozone, a primary component in photochemical smog.
By July, a TiO2-laced concrete was tested through lab and field tests in the Netherlands, which concluded that the material could help cut down air pollution when incorporated into roads.
For the project, researches from Eindhoven University of Technology (TU/e) covered 1,000 square meters (about 10,764 square feet) of a road surface in Hengelo, the Netherlands, were covered with air-purifying concrete paving stones. Another area of the same size was surfaced with normal paving stones for a control group.
Researchers found that the area covered with the air-purifying concrete had a NOx content that was 25% to 45% lower than the one surfaced with normal concrete. Additionally, on average, the NOx concentration was 19% lower of the course of the day and 28% lower in the afternoons only compared to the control street. Under ideal weather conditions, which researchers consider high radiation and low relative humidity, a 45% decrease in NOx concentration could be observed.
In 2014, engineering students from the University of California, Riverside, found that 21 tons of nitrogen oxides per day could be eliminated if tiles on 1 million roofs were coated with a TiO2 mixture they had still been developing.
As part of the project, the students coated two identical off-the-shelf clay tiles with a mixture containing different amounts of TiO2 and then placed inside a miniature atmospheric chamber constructed from Teflon, PVC piping and wood. Using ultraviolet light to simulate sunlight, the students activated the TiO2 to allow it to break down the nitrogen oxides.
Research found that the TiO2-coated tiles removed 88-97% of the nitrogen oxides.
However, this year, the European Commission officially decided to classify titanium dioxide in its powder form as a substance that is “suspected of causing cancer in humans” on Oct. 4.
With the new regulation, titanium dioxide products that are in powder form containing 1% or more of the substance with aerodynamic diameter of 10μm or less are required to carry a cancer warning on the label.