Improving the optical-radiative properties of TiO2 containing coatings - A side effect of air purification

A manifold positive contribution to climate change mitigation and in the improvement of air quality of built environments can be provided by the use of titanium dioxide (TiO2), also - but not exclusively - as coating for building envelope materials, to spread its beneficial effect on the largest surface area possible. The benefits in applying TiO2 coatings - containing in particular the anatase phase - rely, first of all, on the UV-activated photocatalytic degradation of pollutants mediated by it, which can mitigate pollution arising from industrial sources, heating and transportation. Moreover, changes in wettability upon UV irradiation lead to a superhydrophilic state which, coupled with photocatalysis, results in the so called self-cleaning effect, allowing materials to retain a cleaner and more reflective surface over time. Reducing the impact of aging on the optical-radiative performance of built environment surfaces has a strong influence on the thermal comfort and energy consumption of buildings. Here we present a novel effect observed on long-term durability investigations of commercial siloxane paints containing anatase nanoparticles: an increase in reflectance in the near infrared (NIR) wavelength range upon material aging. This could open the door for HNO3 treatment of TiO2 as a method to boost the self-cleaning efficiency and reflectance of surfaces for building, construction and solar technologies.