The 21st Century has brought with it a growing acceptance of the severity of climate change, with Forecasts of the Intergovernmental Panel for Climate Change (IPCC) projecting a 2°C rise in global temperature by 2050 based on current levels of greenhouse gas emissions. The recent Paris Agreement of the 2015 United Nations Climate Change Conference brought a global consensus to make efforts to limit the global temperature rise to 1.5°C by 2050. However, despite such promising commitments, the majority of measures to combat global warming and anthropogenic pollution have so far been directed only towards the prevention of further damage being done. It is likely that more innovative methods may be required to help reverse the accumulation of greenhouse gases and to improve the air quality of urban environments, where smog is having a severe effect on public health.
One such innovation with green potential involves a clever application of catalytic nanoparticles. Refreshingly, this innovation originated from collaboration between the arts and science, and is invigorating in its use of the natural curiosity and creativity of humanity to address man-made issues. Through this article, I aim to describe to you how you yourself can assist in removing harmful pollutants from the air simply by walking along a street, or even just by reading a poem.
Pollutive gases can be broadly divided into two groups: The greenhouse gases (such as methane, carbon dioxide, and nitrous oxide), which absorb radiation in the upper atmosphere, and toxic surface-level pollutants (such as carbon monoxide, volatile organic compounds, and nitrogen oxides (NOx)). Surface-level pollutants are predominantly derived from industrial or transport emissions, and in London alone are believed to be responsible for thousands of premature deaths every year.
Actively reducing levels of air pollutants is likely to require some form of catalytic process (put in mind the catalytic conversion of carbon dioxide to oxygen performed by plants), and so efforts have recently been made to neutralise toxic surface-level pollutants through use of synthetic catalysts in urban environments (where both the concentration of pollution, and people, is at its greatest). These catalysts hold significant promise for the future, and it was through the work of Prof. Tony Ryan that I was first introduced to the potential of one such catalyst, the titanium dioxide (TiO2) nanoparticle.
Nanoparticles are materials on the scale of a millionth of a millimetre. With such miniaturisation comes a substantial increase in available surface area on which reactions can take place, and often a change in chemical properties. When exposed to sunlight, TiO2 nanoparticles provide a catalytic surface for the production of peroxides, which can then react with nitric oxide to produce nitric acid and nitrates, effectively removing the toxic nitric oxide from the breathable atmosphere (1,2).
The current applications of TiO2 nanoparticles include the coating of walls and windows of buildings, and surfaces of pavements and roads (3,5), although the true motive behind this use is not to reduce pollution. TiO2 nanoparticles also confer a self-cleaning property as the lipophilic TiO2 attracts a layer of water between a surface and dirt particles, allowing dirt to simply wash away with rainfall. By such applications alone, concentrations of nitric oxide have been shown to fall by 20-60% (6,7).
A particularly inspirational use of TiO2 nanoparticles arose from the collaboration between Prof. Ryan and the fashion designer, Prof. Helen Storey. This meeting of arts and science led to the development of CatClo, a laundry additive of TiO2 nanoparticles which, when washed into clothing, imbues them with the nanoparticles’ photocatalytic quality. It is predicted that CatClo-treated clothing would remove roughly 5 grams of nitric oxide per day when worn in an urban environment, equivalent to the daily nitric oxide emissions of the average car (8). Although the CatClo additive is eventually removed by subsequent repeated washes, the additional antibacterial effect conferred by the nanoparticles may extend wearable time between washes.
Prof. Ryan has further demonstrated the versatility of TiO2 nanoparticles through an art installation involving prestigious poet, Simon Armitage. Penned by Armitage, a poem entitled ‘In Praise of Air’ was displayed in the centre of Sheffield, printed on 10 m x 20 m material ingrained with TiO2 nanoparticles. This installation was estimated capable of removing the nitric oxide emissions of as many as 20 cars daily.
Just such a merging of arts and science is what separates the projects of Prof. Ryan from other scientific endeavours combating climate change, and it stands as a striking example of how the applications of an invention can be brought to a wider audience by simple, yet creative, means.
More information can be found regarding CatClo at www.catalytic-clothing.org
Post by: David Young
References
1. Ohko, Y., Nakamura, Y., Fukuda, A., Matsuzawa, S. & Takeuchi, K. Photocatalytic Oxidation of Nitrogen Dioxide with TiO2 Thin Films under Continuous UV-Light Illumination. J. Phys. Chem. C 112, 10502–10508 (2008).
2. Toma, F. L., Bertrand, G., Klein, D. & Coddet, C. Photocatalytic removal of nitrogen oxides via titanium dioxide. Environ. Chem. Lett. 2, 117–121 (2004).
3. Shen, S., Burton, M., Jobson, B. & Haselbach, L. Pervious concrete with titanium dioxide as a photocatalyst compound for a greener urban road environment. Constr. Build. Mater. 35, 874–883 (2012).
4. Chen, J. & Poon, C. Photocatalytic construction and building materials: From fundamentals to applications. Build. Environ. 44, 1899–1906 (2009).
5. Hüsken, G., Hunger, M. & Brouwers, H. J. H. Experimental study of photocatalytic concrete products for air purification. Build. Environ. 44, 2463–2474 (2009).
6. TX Active® The Photocatalytic Active Principle. (2009). http://www.italcementigroup.com/NR/rdonlyres/96036B14-4C6D-4E07-9854-1B1CE1AD6593/0/TXactivetechnicalreport2009.pdf
7. Tx Active®. (2006). http://www.italcementigroup.com/NR/rdonlyres/1F30E487-C0A2-4D6F-AB6D-C14555FD866F/0/Scientificresults.pdf
8. Pollution-busting laundry additive gets set to clean. Sheffield.ac.uk (2012). https://www.sheffield.ac.uk/news/nr/catclo-tony-ryan-london-college-fashion-air-purification-nanoparticles-1.211918