Final Report Summary - LIGHT2CAT (Visible LIGHT Active PhotoCATalytic Concretes for Air pollution Treatment) Executive Summary:The goal of Light2CAT is to develop and document a new generation of highly efficient visible-light sensitive titanium dioxide (TiO2) 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 development of a new class of modified TiO2 semiconductor photocatalysts was achieved. These systems showed visible light sensitisation and substantially different nitric oxide oxidation mechanism when compared to ordinary TiO2. Specifically, the selectivity towards nitrates was enhanced, which helps to minimize the amount of NO2 formed during the oxidation reaction. Processes and operative parameters were optimised for the industrialisation and production of the selected photocatalyst on large scale.Research has been conducted to develop cementitious systems able to carry the photocatalysts developed. Initially mortar systems were developed and based on these, final concrete mix designs were engineered, including earth moist photocatalytic concretes for the production of horizontal paving tiles as well as self-compacting photocatalytic concretes for the production of vertical precast elements. A full characterisation of the final concrete elements was performed in order to assess suitability to implement and place the Light2CAT concrete in the built infrastructure of urban and extra-urban environment. Results indicated that the presence of the Light2CAT photocatalyst in the concrete elements does not compromise their main mechanical and durability properties. The concrete elements containing the Light2CAT photocatalyst showed visible light activation and nitrate selectivity being considerably higher than concrete elements containing commercially available undoped TiO2. This signifies that the main objectives of the Light2CAT project were successfully achieved.Three locations were identified for the field study of the Light2CAT photocatalytic concrete materials; one site in the city of Copenhagen (DENMARK), one site in the city of Valencia (SPAIN) and one site along the Danish motorway connecting Copenhagen and Holbæk (DENMARK). The photocatalytic concrete elements were placed in the second half of 2014 and the study conducted until the conclusion of the project in August 2015. Results indicated an abatement of NOx in real world conditions on average between 5 and 20 %. This overall NOx abatement is similar to what was previously reported on materials containing undoped and commercially available TiO2. However, in the case of materials containing ordinary TiO2 the total NOx variation was almost entirely due to a variation in NO content, with often almost no effect on the much more toxic NO2. In the case of materials containing the Light2CAT photocatalyst, the total NOx abatement came from NO and NO2 abatement of the same magnitude, something never reported before in real world conditions. This indicates a clear improvement of the air quality when using the Light2CAT photocatalyst rather than ordinary TiO2, as the former is more effective on the very toxic NO2.Project Context and Objectives:The goal of Light2CAT is to develop new, highly efficient visible-light-activated titanium dioxide for inclusion in concretes to be used in structures across the whole of Europe to improve ambient air quality independent, for the first time, of local climate conditions. 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. Despite vigorous efforts to reduce levels of hazardous substances in the air, targets remain a challenge. One of the most valid sustainable technologies explored so far is photocatalytic concrete. This technology is proven to reduce the amount of hazardous air pollutants up to 80 %. It also imparts self-cleaning properties to built structures, which has a secondary effect of reducing harsh cleaning chemicals entering the water systems. However, the titanium dioxide based photocatalytic building materials are activated by ultraviolet light so, to date, such environmental benefits are limited to countries with a high incidence of sunlight. 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, by implementing in concrete a new generation of eco-efficient, highly active TiO2 photocatalysts 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.The project pursues the following more specific objectives:1. Development and optimisation of TiO2 semiconductor based systems able to exploit visible light to generate charge carriers (valence band positive holes and free electrons) hence providing actual photocatalytic behaviours. Visible light sensitisation would be achieved by employing synthetic techniques including: modification of the ordinary semiconductor crystal structure to reduce the energy gap between valence and conductance bands; metal ion coupling to provide efficient electron sinks at energy lower than the TiO2 conductance band, hence reducing the energy necessary for promoting electrons from valence bands; TiO2 surface hydrogenation able to generate a large number of surface crystal defects that locally reduce the energy band gap. Visible light sensitisation according to techniques like the above would ensure more efficient catalytic removal of polluting emissions within the constraints of cost.2. Implementation of the developed photocatalysts in concrete, establishing suitable methodologies (chemical surface modification, modification of electrokinetic properties, addition of suitable dispersants) to ensure adequate surface dispersion of the photocatalytic materials to obtain concrete surfaces providing high photocatalyst available surface area for pollutant adsorption (hence enhanced photocatalytic performances), high aesthetic and mechanical durability as well as improved resistance towards deterioration phenomena such as attrition, erosion and abrasion, therefore requiring less cleaning, lower replacement levels, and long term reduced resource use.3. Development and application of efficient and durable surface deposition in place of mixing photocatalyst and cement before concrete production (as today’s photocatalytic concrete are obtained using a special cement mixture containing TiO2), reducing the amount of active material in the bulk not reachable by pollutants and light and therefore reducing the overall level of active materials required. This will have the indirect effect of managing the costs of the new materials.4. Optimisation and engineering of photocatalytic concrete for urban paving, outdoor building facades solutions as well as air pollution mitigation motorway (noise, crash and protection) barriers optimised for degrading atmospheric hazardous compounds such as: NOx, SOx and VOCs in areas that do not lie within the sunlight favourable belt and for improving the efficiency (and reducing the seasonal variation in performance) of pollution mitigation in regions of favourable sunlight.5. Engineering of photocatalytic concrete for indoor applications able to promote air cleaning properties by exploiting ordinary indoor lighting to degrade hazardous volatile compounds such as: methane, formaldehyde, short chain alcohols as well as microbial contaminants including mould and bacteria.6. Demonstration of outdoor/indoor applications and measurement and assessment of NOx, SOx and VOCs abatement compared to existing catalytic concretes in a range of relevant indoor and urban sites as well as assessment of aesthetic durability improvement in outdoor conditions.7. Evaluation of the Life Cycle Assessment (LCA). LCA is an objective method to evaluate the burdens associated with all the elements including production and processing, by identifying and quantifying energy and material uses and releases, and to evaluate and implement opportunities to influence environmental improvements. In this project we will assess the life cycle of the product and process encompassing extracting and processing material; manufacturing, transporting and distribution; use, reuse and maintenance; recycling and final disposal.8. Assessment of catalytic lifetime. This objective aims to prove that the photocatalytic activities provided by the final materials are maintained over a period of time comparable with buildings and structures lifetime. This is considered an important issue to address because short catalytic lifetimes could be a barrier for builders and contractors in employing photocatalytic materials.9. Evaluation of the Life Cycle Cost (LCC). Like any other investments, the production should take into account the associated costs, with special attempts to minimise the environmental impact. In this project we will use LCC to yield the present value of the current and future expenditures for the production, use, reuse and maintenance of the selected materials and processes; recycling and final disposal. This will provide the data for companies to be able to present the financial implications of future savings due to additional investments made at present for enhancing performance of the process (e.g. energy efficiency or durability of materials) which can be assessed by end users for decision making.10. Increase the use of photocatalytic concrete technology across European and identify and secure new market sectors such as indoor applications, by engineering the better catalytic efficiency and thus reducing the levels of catalyst required to maintain, or reducing the cost or cost-benefit of the new material compared to existing photocatalytic concretes, removing technical barriers to take up in the otherwise receptive market. A strategy to reduce the cost-benefit ratio is: i. Reducing the total amount of photocatalyst due to higher performances;ii. Efficient and durable surface deposition rather than mixing photocatalyst and cement before concrete production that ends up in losing a lot of active material in the bulk not reachable by pollutants and light.11. Development of input to ISO Standards for evaluation of photocatalytic activities towards NOx, SOx and VOCs abatement for different kinds of photocatalytic concretes (at the moment there is only one ISO standard relative to NOx abatement for photocatalytic paving blocks).12. Assessment of any potential health issues related to the use of nanoparticles in construction materials, in particular in indoor conditions. Although no particular danger is known by the use of nanostructured TiO2 in concrete structures, Light2CAT aims to confirm that these materials do not release nanoparticles that might compromise people health.Project Results:Development/synthesis and test of the photocatalyst, including large scale production:The development of a new class of modified TiO2 semiconductor photocatalysts was achieved. These systems showed visible light sensitisation and substantially different nitrogen oxides oxidation mechanism when compared to ordinary TiO2. Specifically, the selectivity towards nitrates was enhanced, which helps to minimize the amount of NO2 formed during the oxidation reaction. A new method of selectively oxidizing NOx using metal/non-metal codoped TiO2 photocatalysts was developed and a patent application was submitted.Industrialisation and scale up of the synthetic routes was studied. Processes and operative parameters were optimised for the production – on large scale – of the selected photocatalyst, consisting of a metal/non-metal codoped TiO2 photocatalyst. The industrial production of about 700 Kg of photocatalyst was completed. Technical and safety documentation related to this new product were also developed.Development of cementitious systems implementing the photocatalyst and test of the fresh/hardened properties and the photocatalytic properties:Performance indicators of mortar systems containing the Light2CAT photocatalyst highlighted a great potentiality when compared to commercially available, undoped TiO2-based cementitious system. Mortars containing reference undoped, nanosized TiO2 photocatalyst were found to produce too much NO2 as a by-product of the photocatalytic oxidation of NO and NO2 to nitrates. On a long run, this could be detrimental for the environmental remediation process. On the contrary the Light2CAT photocatalyst has shown very high selectivity towards nitrates, forming very little NO2 and effectively reducing the overall toxicity of air containing nitrogen oxides. Furthermore, mortars containing the Light2CAT photocatalyst exhibited activity under visible light irradiation, which was not the case for commercially available, undoped TiO2.Based on the mortar mix designs, final concretes were developed with 4 wt% substitution of cement with the new Light2CAT photocatalyst. Three concrete mix designs were developed; a self-compacting concrete, which can be used for e.g. casting of motorway jersey barriers and two earth moist concretes for production of e.g. paving tiles. The fresh and hardened properties were documented and it was shown that the TiO2 photocatalyst in itself did not have a negative influence on the durability properties of the concrete.As far as the performances are concerned, two photocatalytic cementitious renders containing respectively Light2CAT photocatalyst and a reference commercial anatase photocatalyst were tested under three light sources with different UV irradiances. When using the fluorescent light simulating solar radiation, the two renders containing the different photocatalysts exhibited similar total NO abatement. When the amount of UV in the incident light decreases of an order of magnitude, the activity of both the photocatalytic renders drop (as expected), however the render containing the Light2CAT photocatalyst is 15 % more active (as total NO abatement) than the one containing the undoped TiO2. The situation becomes even more advantageous for the Light2CAT photocatalyst-based materials when a LED warm light with almost no UV at all is used. Whilst the undoped TiO2-based cementitious render showed a total NO abatement approaching zero, the Light2CAT one maintained an overall NO conversion of about 15 %. These results are of fundamental importance; the fluorescent light tube warm white 830 and LED warm white are typical light sources used in indoor environment, therefore these evidences show the great potential for the Light2CAT photocatalyst to be used as an effective visible light active depolluting strategy in indoor environments or highly NOx polluted road tunnels. As to the latter, a few tunnels throughout Europe are nowadays coated with undoped TiO2-based cementitious renders, however highly power consuming UV light sources are in place to activate the photocatalyst. The use of the Light2CAT photocatalyst instead would allow using cheap and low power LED or fluorescent lights, therefore reducing the energy consumptions of the installation and positively contributing to the economy of the infrastructure.The other major advantage that was discovered when using the Light2CAT photocatalyst in concrete, is the very high selectivity towards nitrates compared to concrete containing ordinary, undoped TiO2 photocatalyst. In the case of concrete with the reference undoped TiO2, only 20 % of the total converted NO ended up as nitrates, i.e. the final desired harmless product. This means that this catalyst has the potential of forming too much of by-products that could make the air remediation not optimal. The situation is very different when the newly developed Light2CAT photocatalyst was used. With a nitrate selectivity about 80 %, the Light2CAT photocatalyst effectively oxidises nitrogen oxides to the harmless desired product, optimising the air remediation process. The significance of this advancement in terms of nitrate selectivity is paramount, as this signifies that the Light2CAT photocatalyst can effectively:1. Directly lower the amount of NO2 in the air;2. Indirectly reduce the amount of ozone produced by NO2 photolysis (and followed reaction with molecular oxygen).Last, but not least in importance, the implementation of the Light2CAT photocatalyst in concrete can help to develop “easy-to-clean” concrete surfaces. This was demonstrated by staining two concrete surfaces, one with the Light2CAT photocatalyst and one with no photocatalyst at all, with a red dye (Rhodamine B) and subsequently irradiating with a lamp (Osram Ultravitalux UV-A lamp) simulating solar radiation. After about 12 hours of irradiation, the red colour completely disappeared from the surface containing the Light2CAT catalyst, while the surface of concrete without photocatalyst remained red.Full scale demonstration of the air cleaning properties of concrete containing the photocatalyst at different locations:The full scale demonstration involved three demonstration sites; two in Denmark (a city street in Copenhagen and a motorway outside Copenhagen) and one in Spain (a city street in Valencia). These were chosen to demonstrate the developed TiO2 photocatalyst in different sunlight belts (least and third most favourable belt respectively) and in different environments (urban environment and along motorway). In this context, it was also demonstrated that the industrial scale production of concrete elements containing the TiO2 photocatalyst was feasible and that the mechanical and durability properties were acceptable. A number of jersey barriers were produced using the developed self-compacting concrete containing the photocatalyst and a large number of paving tiles were produced using the two developed earth moist concretes containing the photocatalyst.Equipment was set up to monitor the concentration of NO, NO2 and NOx in the air at the three locations. For the city street in Copenhagen, data was obtained over a whole year before placing the photocatalytic tiles and a whole year after. For the motorway outside Copenhagen and the city street in Valencia, data was collected over a total of half a year.The results generally indicated an abatement of NOx in real world conditions on average between 5 and 20 %. This overall NOx abatement is similar to what was previously reported on materials containing undoped and commercially available TiO2 (at Northern latitudes). However, in the case of materials containing ordinary TiO2 the total NOx variation was almost entirely due to a variation in NO content, with – often – almost no effect on the much more toxic NO2. In the case of materials containing the Light2CAT photocatalyst, the total NOx abatement came from NO and NO2 abatement of the same magnitude, something never reported before in real world conditions. This indicates a clear improvement of the air quality when using the Light2CAT photocatalyst rather than ordinary TiO2, as the former is more effective on the very toxic NO2. This once again can be considered the direct consequence of the much greater selectivity of the Light2CAT photocatalyst towards nitrates.Confirming what was expected from the laboratory results, the three field test studies concluded that:1. 56.5 % NOx reduction – from 84.0 to 36.5 ppb in Valencia and 18.9 % NOx reduction – from 26.2 to 21.3 ppb in Copenhagen.2. Along the motorway in Denmark, abatement of total NOx was assessed around 10 % under favourable total solar irradiance conditions (>600W/m2).3. In the city of Copenhagen, the total NOx concentration during the photocatalytic period seems to be constantly lower than the reference one. This independently on the concentration of UV light in the solar radiation reaching the surface. On the contrary, a previous study employing undoped TiO2 found that a threshold of ca. 2.5 % of UV fraction of total light irradiance at solar noon (corresponding to a total UV energy delivered to the surface equal to 600kJ/(m2 day)) was necessary to achieve a true photocatalytic effect.4. In summer along the motorway, between sunrise and 9 am and between 4 pm and sunset, the Light2CAT was able to remove 12.64 % of NO and 7.37 % of NO2. This is hard to reconcile with photocatalytic activity promoted by UV photons only, as in this part of the day UV concentration is minimum.5. Point 3 and 4 seem to be evidence for a significant level of visible light photocatalysis associated with the Light2CAT materials; proven in real world scenarios besides commonly adopted laboratory tests.6. Most importantly, the amount of NO2 (i.e. the most toxic and dangerous species amongst nitrogen oxides ordinarly present in the atmosphere) removed is unprecedentedly higher than what found in other existing reports related to the nitrogen oxides abatement capabilities of commercially available TiO2. This is the consequence of the greater selectivity towards nitrates exhibited by the Light2CAT photocatalyst when compared to ordinary TiO2.7. This high selectivity is a major benefit for environmental remediation technologies. The catalyst works well in lowering the amount of NO2 in the air, and indirectly reducing the amount of ozone produced by NO2 photolysis and followed reaction with molecular oxygen. These benefits are not achievable with undoped TiO2, as its selectivity to nitrates is – often – not high enough.Potential Impact: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. 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, which allows in the presence of water and oxygen (i.e. common atmospheric conditions) to 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.To date, such environmental benefits have not been possible neither 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 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 by implementing in concrete a new generation of eco-efficient, highly active TiO2 photocatalysts, showing a higher degree of activation under visible light conditions and higher nitrate selectivity in order to minimise the amount of NO2 in the atmosphere. The aim is to remove climate and seasonal considerations from the application of photocatalytic building materials and encompassing efficient indoor applications too.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 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 the concentration of gaseous pollutants in proximity of the emission source, preventing further diffusion to the surrounding environment.The use of the TiO2 photocatalyst in cementitious and construction materials for removing nitrogen oxides from the air in urban environments have been widely studied and applied from the mid 1990’s. In all these years scientific research has mainly focused on developing catalysts able to reduce the overall amount of NOx (i.e. the total concentration of nitric oxide NO and nitrogen dioxide NO2) and (more recently) be sensitised by visible light (pure TiO2 is active only under UV irradiation). In the past two years, the international photocatalysis community and researchers throughout the world have started addressing important questions regarding the selectivity of the overall DeNOx process. Specifically, when photocatalytically oxidising nitrogen oxides the desired final compound is nitrates, i.e. harmless minerals like the ones found in drinking water. The thorough analysis of decades of laboratory measurements published in the literature, new projects (Light2CAT played a major role here…) together with several well-assessed field studies have highlighted however, that ordinary titanium dioxide might not be the best choice, as sometimes it forms too much NO2 (when oxidising NO) with very low selectivity towards nitrates. Considering that NO2 has been proven to be from 5 to 25 times more toxic than NO, it is clear that reducing the total NOx amount is not enough to guarantee an improvement of the air quality. Some commercially available titanium dioxides form so much NO2 that, although reducing the total NOx loading, the overall quality of the air is actually worsened rather than improved. These experimental evidences constitute a significant scientific breakthrough; however they could pose a major threat for companies commercialising photocatalytic products based on ordinary TiO2. The Light2CAT project has developed a photocatalyst that together with being sensitised by natural solar light is highly selective towards nitrates, producing very little amount of NO2 when compared to ordinary titanium dioxide. This method of selectively oxidising NOx is the subject of a patent application.The Light2CAT project is already generating a valuable impact as measured by the following socio-economic indicators:1. The highly selective photocatalyst is forecasting to provide the partners involved a unique market position, ahead of the competition.2. Selectivity and visible light sensitisation are fundamental unique selling point for the Light2CAT industrial partners in order to reinforce their presence in a market (the one of photocatalytic products) which is estimated to be valued at nearly $1.6 billion in 2015 and projections are showing a Compound Annual Growth Rate of 12.6%, reaching nearly $2.9 billion by 2020.3. Commercial methodologies for exploiting the foreground are currently being discussed, developed and optimised by the industrial partners of the Light2CAT project, who are in the phase of preparing a commercialisation agreement based on the business plan. This agreement will be soon finalised, as companies outside the Light2CAT consortium have already shown interest in implementing and using the Light2CAT technology.4. Light2CAT is already promoting actions towards standardisation as there is presently no clear EU-wide regulatory framework for photocatalytic materials. This also in relation to binding the products to existing certification systems (e.g. LEED, BREEM) for a more favourable market introduction.5. Cost of health. The large scale implementation of technology capable of reducing air pollution and improving air quality – in particular if passive technologies based on the exploitation of solar energy – could indirectly impact – on a long term – on the National and European investment for health care related to respiratory pathologies or problems linked to poor air quality. This is of fundamental importance as “air pollution costs European economies US$ 1.6 trillion a year in diseases and deaths” according to the World Health Organisation, Regional Office for Europe (Copenhagen, 2015).Together with the socio-economic indicators described above, during the Light2CAT project seven scientific articles in peer-reviewed journals were published and one is currently under submission. Twenty-five large audience dissemination activities were undertaken, including several oral presentations/articles for major international conferences on photocatalysis. One of the most notable dissemination events to which Light2CAT was presented was the Ecobuild faire in London during the beginning of March 2015. Ecobuild is one of the leading exhibitions in the construction field. It attracts over 40,000 industry professionals annually from the entire built environment supply chain. Visitors typically exhibit the latest products, reveal cutting edge technology and build relationships for the future. A 20 m2 booth of the Light2CAT project was set up to explain the projects’ results and potential market outcomes. A small demonstrator was produced, which consisted of a small reproduction of London’s city centre made out of 3-D engraved photocatalytic cement, demonstrating in-situ the easy-to-clean properties of the new cement. A notable output of the project was the production of a short video, in the form of a cartoon, which was used to provide a simple explanation of the project’s concepts. The video is presently visible on youtube and posted on the project’s website and social media pages (facebook). The Light2CAT project has been often featured on national press releases (in Denmark, Spain, Italy and Sweden) including a report/interview broadcasted on the national Danish TV news and national radio.List of Websites:www.light2cat.eu Related documents final1-light2cat_diagrams.pdf
