Development of a versatile experimental setup for the evaluation of the photocatalytic properties of construction materials under realistic outdoor conditions

The interest on outdoor photocatalytic materials is growing in the last years. Nevertheless, most of the experimental devices designed for the assessment of their performance operate at controlled laboratory conditions, i.e., pollutant concentration, temperature, UV irradiation, and water vapor contents, far from those of real outdoor environments. The aim of the present study was the design and development of an experimental device for the continuous test of photocatalytic outdoor materials under sun irradiation using real outdoor air as feed, with the concomitant fluctuation of pollutant concentration, temperature, and water vapor content. A three-port measurement system based on two UV-transparent chambers was designed and built. A test chamber contained the photoactive element and a reference chamber to place the substrate without the photoactive element were employed. The third sampling point, placed outdoors, allowed the characterization of the surrounding air, which feeds the test chambers. Temperature, relative humidity (RH), and UV-A irradiance were monitored at each sampling point with specific sensors. NOx concentration was measured by a chemiluminescence NOx analyzer. Three automatic valves allowed the consecutive analysis of the concentration at the three points at fixed time intervals. The reliability of the analytical system was demonstrated by comparing the NOx concentration data with those obtained at the nearest weather station to the experimental device location. The use of a chamber-based reaction system leads to an attenuation of NOx and atmospheric parameter profiles, but maintaining the general trends. The air characterization results showed the wide operating window under which the photoactive materials should work outdoors, depending on the traffic intensity and the season, which are reproduced inside the test chambers. The designed system allows the measurement of the photoactivity of outdoor materials or the comparison of several samples at the same time. The suitability of the system for the evaluation of the DeNO(x) properties of construction elements at realistic outdoor conditions was demonstrated. The designed experimental device can be used 24/7 for testing materials under real fluctuations of NOx concentration, temperature, UV irradiation, and relative humidity and the presence of other outdoor air pollutants such as VOCs, SOx , or NH3. The chamber-based design allows comparing a photocatalytic material with respect to a reference substrate without the photoactive phase, or even the comparison of several outdoor elements at the same time.