Development and evaluation of the efficiency of photocatalytic pavement blocks in the laboratory and after one year in the field

Nitrogen oxides (NOx) are currently one of the main causes of poor air quality in large cities. A promising approach to reducing high concentrations of this pollutant is the photochemical conversion of NOx   to nitrate ions (NO3-), using semiconductors like titanium dioxide (TiO2). This paper presents the results of a research study on the nano-modification of the surface of pavement blocks, with the aim of purifying the air in large cities through the degradation of NOx. To this aim, blocks were produced with a photocatalytic surface through the incorporation of titanium dioxide. Three photocatalytic mortar layer thicknesses (3, 6 and 10 mm) were tested, as well as two types of TiO2 (rutile and anatase) and three levels of TiO2 content incorporated (3%, 6% and 10%). After the evaluation of the photocatalytic efficiency in the laboratory, the photocatalytic pavement blocks were applied in the field and after one year in service the photocatalytic efficiency was reevaluated in the laboratory. The experimental results indicate the good efficiency of the new photocatalytic blocks in the degradation of NOx, which under certain conditions can reach a pollutant (NOx) conversion rate of up to 95%. However, after one year in the field the blocks showed a significant reduction in photocatalytic efficiency. It was also observed that the blocks with more porous surfaces showed better results for the rate of NOx degradation. Furthermore, by increasing the content of TiO2 greater efficiency can be obtained.

► The efficiency of photocatalytic blocks is dependent on the type and percentage of TiO2 incorporated.
► The surface texture of the photocatalytic block is a determinant factor for the efficiency in the degradation of NOx.
► After one year in the field the photocatalytic blocks presented a significant reduction in efficiency.
► A simple cleaning of the surface of the photocatalytic blocks did not recover the efficiency lost.
► The formulation of the photocatalytic concrete should be developed according to the location of application.