The goal of Light2CAT is to develop new, highly efficient visible-light sensitive titanium dioxide for inclusion in concretes to be used in structures across the whole of Europe for improving ambient air quality independent, for the first time, of local climate conditions. To date, such environmental benefits have not been possible either indoors or outside of the Mediterranean countries because existing photocatalytic concrete does not perform well in conditions of low sunlight or under Northern skies since the TiO2 contained in it is only activated by ultraviolet (UV) light.
The need to improve air quality in European Countries has been identified as a major requirement to be achieved within the next decade in the effort to control climate change, a key Europe 2020 strategy, and to improve human health. Council Directive 2008/50/EC lays the foundation for a common strategy to define and establish objectives for ambient air quality in the EU. In terms of air quality, there are three main groups of pollutants, 1) primary particulate matter and secondary particulate matter precursors, i.e. oxides of nitrogen (NOX,), sulphur dioxide (SO2), and ammonia (NH3); 2) ozone precursors, i.e. volatile organic compounds (VOC) including methane (CH4), NOX and CO; and 3) acidifying pollutants, i.e. NOX, SO2, and NH3. Within the framework of the Directive, yearly emission limits and alert threshold limits have been designated for the hazardous substances sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air. Earlier legislation relating to air pollution such as the National Emission Ceilings Directive (2001/81/EC) also sought to limit hazardous substances such as NOx, sulphur oxides, and volatile organic compounds. Despite vigorous efforts to reduce levels of these substances, these targets remain a challenge. According to recent data published in May 2010 by the European Environment Agency, around half of the European Union's Member States expect to miss one or more of the legal limits set for 2010 by the National Emission Ceilings Directive. New efforts are required in respect of the 2008 Directive on ambient air quality and cleaner air for Europe including, the focus of this project, the development of better technologies.
One of the most valid sustainable technologies to improve ambient air quality explored so far is the application of semiconductor photocatalysis in construction and cement science. Titanium dioxide, TiO2, a white solid, stable and non-toxic semiconductor oxide, can be activated by light and, in the presence of water and oxygen (i.e. common atmospheric conditions), mineralise organic molecules and oxidise or remove inorganics, achieving mitigation of air pollution. Incorporating TiO2 in concrete also results in self-cleaning properties of outdoor building facades in contrast to the usage of harsh cleaning chemicals that can enter sewerage systems and water treatment plants. This technology has proved to reduce the amount of hazardous air pollutants up to 80 %. An assessment made by Zhu et al. in 2004 showed that the implementation of UV activated TiO2 in concrete over a total area of about 7000 m2 of roadway in Milan (Italy) resulted in a 60 % drop in NOx concentration in the air in 2002 compared to the relative value in 2001.
The concept of this project is therefore to extend the use of photocatalytic concretes capable of degrading atmospheric hazardous compounds to areas within the less favourite sunlight belts, Figure 1.1a, by implementing in concrete a new generation of eco-efficient, highly active TiO2photocatalysts showing a much higher degree of activation under visible light conditions. The aim is to remove climate and seasonal considerations from the application of photocatalytic building materials and, through higher conversion efficiencies of the catalytic components, to reduce production costs, facilitating take up of the technology.
Despite measurable success over the last decade in reducing emissions, road transport continues to be a major source of pollutants including NOx, contributing (in 2008) 41% of total NOx emissions. The main field of application of the novel photocatalytic concretes targeted in this project is urban structures including buildings affected by high levels of NOx/SOx/VOCs since they offer an optimised solution for reducing hazardous air pollutants. These structures include street canyons, squares, pavements, etc..., and motorway noise, crash and protection barriers which are able to reduce the level of nitrogen oxides and other air pollutants from traffic thus guaranteeing a better air quality for the workers of construction sites (through use of photocatalytic protection walls). In general, concrete structures on roads and motorways, and blocks of paving are large and offer a substantial surface area that can be exploited by Light2CAT to implement suitable active photocatalyst to reduce, by at least 50%, the concentration of gaseous pollutants in proximity of the emission source, preventing further diffusion to the surrounding environment. Visible light activation of the photocatalyst also leads to the potential for extending the application of the new concrete to improve indoor air quality in public buildings and homes. The potential scope for indoor applications will also be tested and demonstrated in this project.