This year’s theme for UN World Environment Day is improving air quality. With so many avenues to explore, photocatalytic materials are seen as one way to reduce air pollution. Several LIFE projects are using real-time measurements to demonstrate their effectiveness.
Research on how photocatalysis can be used to eliminate emissions has been ongoing for some years. But most studies do not venture to the point of real-life, real-time testing. LIFE funding for the projects DIGITALIFE, LIFE PhotoScaling and PHOTOCITYTEX allow researchers to produce and test textiles and ceramics in real-world conditions in places like hospitals or on the streets of Valencia and Madrid.
Risks and opportunities
While EU law sets emissions limits for pollutants such as nitrogen dioxide (N02), the average annual concentrations can still exceed these. NO2 limits are set to 40 µg m3, but still regularly exceed 50 µg m3 in some cities.
The costs of pollution to human health are well established; it is responsible for an estimated 400 000 premature deaths every year in Europe, according to a 2018 report [pdf] from the European Environment Agency (see page 8). Pollution is also linked to damage to the environment, affecting water and soil quality and the flora and fauna which depend on them.
Titanium dioxide (TiO2)-based products have been developed and tested within LIFE projects to reduce air pollution. TiO2 is highly efficient at degrading atmospheric pollution such as nitrogen oxides and ethanol. It works as a catalyst to break down pollution molecules in combination with light and humidity.
Digitally printing photocatalytic tiles
The DIGITALIFE project introduced a low-resource, digital printing production method to manufacture ceramic tiles coated with titanium dioxide powder. Traditionally, these manufacturing processes use a significant amount of water, energy and titanium dioxide.
“We needed to thoroughly investigate the possibility to build a printer which would work with ink containing TiO2 powder,” explained Mr Valentino Capucci from the Italian Iris Ceramica Group, one of the beneficiaries. “The main problem was to formulate a stable and active ink ready to be printed on the ceramic tiles and then heated at 680°C.”
The team took advantage of advances in digital printing to apply the pollution-absorbing coating. The final product was a stable and vitrified surface where TiO2 particles are completely fixed and impossible to remove. This means a healthier work environment, especially in hospitals, partly because no harmful nano-sized particles are used in production.
The digital printing process reduced CO2 emissions by 89%, cut TiO2 by 50% and almost completely eliminated the use of water.
With help from LIFE funding, Iris Ceramica was able to work together with another Italian company and researchers from the University of Milan, and have a team completely devoted to the project. Its product is called Active, and is on the market in the building sector. “Thanks to the project results,” Mr Capucci added, “we now have a product that is more photocatalytically active than before, and can cover even larger tiles up to 1.5m by 3m in size.”
Self-cleaning hospital surfaces
The Active ceramics product is antibacterial and self-cleaning as well as anti-pollution and anti-odour. “This means hospitals can have antibacterial surfaces which can be cleaned with only mild soaps, avoiding toxic and expensive detergents”, explained Mr Capucci.
An ‘Active 2.0’ is also now on the market, thanks to follow-up work done after the LIFE project. Under a pending patent, the new product works under LED light and is even antibacterial in the dark.
Boosting confidence to use photocatalytics
“Photocatalytic products are already on the market, but do not always take off commercially because administrations and the wider society are not confident enough in them.” This was the basis for the project LIFE Photoscaling, explained Ms Marta Castellote, senior researcher from Instituto de Ciencias de la Construcción Eduardo Torroja-CSIC.
LIFE Photoscaling tested materials supplied to them by producers, including products from DIGITALIFE. “Administrations are the main customers for these types of products,” said Ms Castellote, “so we wanted to answer their doubts. A decision support tool developed within the project will allow administrations to implement photocatalytic products confidently.”
By seeking to make photocatalytic products more attractive, the LIFE Photoscaling project responded to a real need to scale up production and implementation. “LIFE funding was a miracle for us because it meant we had enough money to research without needing to involve partners with commercial interests.”
Street worthiness and wider city use
Researchers on the LIFE Photoscaling project set up air sampling equipment for selected photocatalytic products which teams applied on 2 platforms, constructed ad hoc at the premises of the IETcc, at pilot plan scale in areas of Madrid. It also ran simulated real-world tests such on factors such as durability and leaching of titanium dioxide and airborne TiO2 nanoparticles. Finally, the tool developed was validated in one street in Madrid. One method was to use a mobile device to simulate the effects of passing traffic.
“We showed that an initial test of photocatalytic activity is not enough to ensure confidence”, said Ms Castellote. “You need to evaluate the performance, intrinsic durability and possible unwanted side-effects of using the products.”
LIFE Photoscaling was presented at the World Chemistry Forum in May 2019 in Barcelona.
Decontamination in urban spaces
Like DIGITALIFE, LIFE PHOTOCITYTEX also developed materials using the particular properties of TiO2. The project has shown highly promising results in improving air quality from both controlled and real-life demonstration field work.
A team from the Spanish Fundación Centro de Estudios Ambientales del Mediterráneo (CEAM) produced special awnings and tarpaulin wall coverings spun with photocatalytic fibres. These were first tested in CEAM’s simulation chambers at the EUPHORE centre before being installed on streets in Valencia: one location in a motorway tunnel and another near a city schoolyard.
"Working at the EUPHORE chambers meant a change of scale: from laboratory and semi-industrial scale to demonstrating the depolluting effect of the photocatalytic textiles in a higher scale using the high volume simulation chambers, i.e. under almost real and controlled conditions," explained Dr Amalia Muñoz from the centre. With a focus on the pollution nitrogen oxide (NOx), researchers found that their products resulted in
- up to 96% NO2 reduction per hour using photocatalytic awnings;
- 40% reduction over 8 hours using photocatalytic wall coverings.
In 2.5 years of real-life testing in Valencia, results were just as positive.
NO2 levels were cut by an average of between 43-54% in the presence of the awning prototypes during November 2014 to March 2017, and 23-45% using tarpaulins on the walls of the motorway tunnel.
With these photocatalytic fabrics already developed at real-scale for demonstration purposes, the next step is to integrate them in the production chain of AITEX, the project beneficiary, said Dr Muñoz. "Initially, establishing this product in the market would impact existing textile companies producing these fabrics and widening their production. It would also foster the birth of new high-tech companies within the sector. Beyond this, the main impact would be on other sectors such as construction, architecture, textile and design."
Related information on the EU’s air quality strategy
This article was updated 5 June with quotes from LIFE PHOTOCITYTEX