Photocatalytic activity of neat and polymer-modified bitumen

In recent years, the implementation of inorganic photocatalysts in road-paving materials has been explored as a promising solution for the degradation of volatile pollutants produced by both automotive vehicles and civil/industrial activities. However, this study shows that asphalt binders, an essential component of asphalt mixtures, already possess intrinsic photocatalytic properties induced by the inorganic and organic semiconductors, which are among their numerous components. The activity of three different samples of bitumen has been assessed in comparison with that obtained on bitumen modified with TiO₂ Evonik P25, a widely used inorganic photocatalyst. The activity tests have been performed towards a model volatile molecule (2-propanol) under simulated solar radiation. The activity of neat bitumen samples was significant towards the photooxidation of 2-propanol to acetone, and, surprisingly, the mass incorporation of significant amounts (5 %_w/w) of TiO₂ nanoparticles resulted only in a modest enhancement of its activity. These results, along with tests in aqueous phase where 4-nitrophenol and benzyl alcohol have been converted, indicate that the intrinsic activity of bitumen is of utmost relevance, despite it not being reported in previous studies. FT-IR and ICP-MS characterizations have been utilized to provide indications on the potential inorganic and organic semiconductor components being responsible for this phenomenon. AFM and TGA have provided further information on the used bitumen samples.