Abstract
Industrial activities and road traffic are the main causes of the emission of pollutants such as SO2, NOx, and volatile organic compounds (VOCs). According to the World Health Organization, more than 90% of the world's population lives in places where pollutant concentrations exceed their limits. Devoted to the field of environmental remediation, heterogeneous photocatalysis mediated by semiconductors, such as TiO2, has recently attracted significant interest due to its capacity to efficiently convert solar energy into chemical energy which can photodegrade harmful pollutants. Several research studies achieved promising results related to the degradation of different pollutants emitted by fossil fuels used by road vehicles. Due to the huge surface area of photocatalytic
asphalt pavements and its vicinity to the exhaust gases from automobiles, they are quoted as promising surfaces for the reduction of SO2, NOx, hydrocarbons and other VOCs present in the atmosphere, but also to photodegrade soot as the accumulation of cars' fuel combustion in areas with heavy traffic.
For TiO2, this only occurs in the presence of Ultraviolet (UV) light from sun irradiation and moisture/O2. However, the sunlight is mostly composed of visible and infrared photons, with only about 3%–5% of the solar spectrum comprising the UV range. In this sense, one of the most important concerns reported in recent literature to obtain improved photocatalytic materials is the doping of TiO2 particles with different materials, such as Ce, Cu, and Fe. To obtain photocatalytic asphalt mixtures, three main techniques can be mentioned for applying the semiconductor materials to the asphalt mixtures: (i) spray coating, (ii) volume incorporation, and (iii) binder modification. Spray coating is most likely the most efficient functionalization technique, as it uses smaller amounts of semiconductor material that are all situated at the surface of the pavement. However, the immobilization of the semiconductor particles over the asphalt mixtures surface is still a major challenge. Binder modification leads to a lower photocatalytic efficiency, but it will provide a better immobilization and also improved rheological properties. A significant concern that should be considered as well in both application methods, is the dispersion of the TiO2 nanoparticles. Otherwise, they may agglomerate and, consequently, decrease the photocatalytic efficiency even further.
In conclusion, the main objective of this project is to study the major challenges towards a solar-active photocatalytic asphalt mixture which is both efficient and durable. This includes implementing the latest developments regarding modified TiO2 nanoparticles and studying important aspects as dispersion and immobilization.
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