Dark and light mediated NO2 abatement by TiO2- and WO3-polyaniline nanocomposites

Air pollution is considered one of the largest environmental issues that developed and developing nations is facing nowadays, due to overpopulation. Nitrogen oxides are serious primary air pollutants generated by human activities (automobile engines, industrialization and deforestation) and are also responsible for acid rains, photochemical smog, and health diseases. The scientific and industrial communities are hardly working to reduce NOx emissions into the air and numerous strategies have been developed. Among them, photocatalysis has shown an outstanding potential to fight NOx pollution. TiO2 is a photocatalyst model and well-known in the market due to its excellent chemical stability, wide availability and low cost and photocatalytic performance in UV light range. It has shown great potential towards NOx abatement. However, even though TiO2 is highly active under UV light irradiation, its activity under visible light is very low and in the dark it is completely inactive. Recently, conducting polymers/metal oxides composites have been developed to enhance the activity of these semiconductors under visible light towards aqueous pollutants degradation, but the scientific literatures lack on their use towards air remediation. Polyaniline (PANI), is one of the main exponent of the class of conducting polymers and could strongly contribute to the NOx abatement thanks to its redox properties, related to the presence of imino-quinoid/amino-benzenoid groups, and to its sorption ability. In the present study, PANI/TiO2 and PANI/WO3 nanocomposites were synthesized by an innovative green UV-assisted procedure, properly characterized, and applied to the NO2 abatement under light irradiation and in dark conditions. It was demonstrated that the polymeric component acts by a double mechanism: reducing of NO2 to the corresponding 40 times less toxic NO and adsorption both under radiation and in the dark. Moreover, the materials maintained high efficiency up to four runs without any regeneration treatment.