Pollutants are transformed into harmless products that can be washed away by the rain
Nanoparticles of TiO2
onto fabrics can purify the air
sprayed technology could clean
the air of cities and towns by removing harmful nitrogen oxides, sulfur oxides and volatile organic compounds
e are all familiar with the dangers associated with climate change. Global warming and carbon
emissions make headlines in the developed world, with wider, mostly sulfur-based pollution prevalent in the coal-burning developing economies. There is much less talk about another silent and pervasive killer that is a menace to our society and whose effects on everyday life go beyond global warming: NOx. Oxides of nitrogen – nitrogen oxide
(NO), nitrogen dioxide (NO2) and nitrous oxide (N2O), known collectively as NOx
respiratory disease, such as asthma, as it tends to affect the lower airways of the lungs (bronchioles and alveoli). NOx also contributes to ground-level smog, ozone formation and acid rain, nitrous oxide is a potent greenhouse gas. In September 2011, the World Health
– are formed during the combustion of fossil fuels like coal and gas. These gases can cause serious respiratory problems – NO2
Organization (WHO) estimated that urban air pollution causes 1.3m deaths/year worldwide. There is no easy solution to the problem even as work continues to develop better technologies to remove
22 Chemistry&Industry • November 2012 is a major contributor to
pollution at source. But as more cars and trucks are put into service globally and as more energy is needed to sustain the world’s growing population, the problem is likely to continue to grow. Both national and international authorities are aware of the dangers of NOx, and have attempted to tackle the issues through legislation. Unfortunately, air emissions targets remain largely unmet for key pollutants, including NOx, particulate matter (PM) and other volatile organic compounds (VOCs) that affect our environment and health. There is a need for investment in more novel and active chemical solutions.
NOx abatement For nearly 30 years, catalysts have been used in systems to control air pollution ‘at source’, with those targeting NOx based primarily on TiO2
products have been developed to reduce NOx emissions from diesel vehicles to meet stringent emissions regulations. These products are now widely used
are widely used in both coated and extruded forms to control NOx emissions. Since the mid-1980s, these products have been used in power plants that burn coal or gas to produce electricity. More recently, from the mid-2000s, TiO2
. Ultrafine TiO2 -based powders 1.3m
Approximate number of deaths every year caused by urban air pollution
in the automotive industry around the world.
However, while controls at source are the primary form of pollution control, they are not the complete solution. More needs to be done to deal with particle and NOx emissions that have either escaped from cars or power plants, or are formed via combustion reactions in the atmosphere. Here photocatalytic products, such as Cristal’s CristalACTiV, which can be added to paint, or used as a surface coating for building materials such as concrete, glass and steel, and even textiles, look promising. The treated materials can transform NOx in the air into harmless products that can be washed away by the rain.
TiO2 technology Ironically, the sun is both at the heart of air pollution – it drives the smog cycle – and it can be at the heart of the solution as well, in the use of photocatalysts. A photocatalyst is a semiconducting