Pollution-busting concrete
Since the mid-1990s, a photocatalyst called titanium dioxide (TiO2) has been included in certain concrete materials to remove polluting nitrogen oxides from the air. While TiO2-containing concrete can remove up to 80 % of air pollution, its requirement for ultraviolet (UV) light limits its application to areas with high sunshine. Funded by the EU, the LIGHT2CAT (Visible light active photocatalytic concretes for air pollution treatment) project made photocatalytic concrete using a form of TiO2 that can be activated by visible light. This modified TiO2, which oxidises nitrogen oxides into nitrates (harmless minerals found, for example, in drinking water), is also more selective than its predecessor. While normal TiO2 sometimes oxidises nitrogen oxide (NO) into the highly toxic air pollutant nitrogen dioxide (NO2), LIGHT2CAT demonstrated that its product produces minimal NO2. Apart from directly lowering the amount of NO2 in the air, this will indirectly reduce the amount of NO2-derived atmospheric ozone. Based on laboratory tests, LIGHT2CAT developed 3 different concrete mixes containing 4 % photocatalyst, and tested them under different light sources. Researchers found that under reduced UV conditions their photocatalyst-cement composites were 15 % more active than cements containing ordinary TiO2. Importantly, when non-UV LED warm light was used, LIGHT2CAT's cement remained active while ordinary TiO2-based cement showed zero activity. After scaling up production of their cement-photocatalyst composites, researchers tested prototypes in several study sites in Denmark and Spain. They demonstrated for the first time that under real-world conditions, their product removed both NO and NO2 from the air. LIGHT2CAT's pollution-busting concrete may be used for concrete structures on roads and motorways, blocks of paving and outdoor building facades. An added bonus is that this material is self-cleaning and may reduce the amount of harsh cleaning chemicals entering water systems.
Keywords
Concrete, buildings, air pollution, titanium dioxide, nitrogen oxides, LIGHT2CAT, photocatalytic
