Removal of black carbon using photocatalytic silicate-based coating: Laboratory and field studies

This study investigates how two photocatalytic titanium dioxide (TiO2) contents (1.6% and 2.5% by volume) in liquid silicates remove black carbon (BC) (8 and 24 μg cm−2) on mortars to recover surface chromaticity (black to white color, L*) and solar reflectance (SR). A new method linking non-intrusive measurements of L* with SR is developed to rapidly diagnose soiling susceptibility and self-cleaning effectiveness of opaque building surfaces. The higher TiO2 content of 2.5% restores soiled surfaces faster than the 1.6% TiO2 in silicates by at least 20 h, although the latter can fully recover appearance from a lower BC loading (8 μg cm−2). Tripled BC loading signifies the need and superior self-cleaning capability of the higher TiO2 content. Laboratory studies characterize the temporal trend in organic bleaching and evidence its delay of BC degradation. A 3.5-year field study validates the applicability of the L*-SR assessment and demonstrates the reduction of a total heat burden of >790 kWh m−2, as well as removal BC-equivalent pollutants of 16 g m−2 by the photocatalytic coatings. Taking together pollutant deposition flux, TiO2 content, solar insolation, appropriate references and sufficient monitoring duration, performance of photocatalytic building coatings can be evaluated for other locations with varied air quality and environmental conditions.