Developing Advanced TiO2-based Nanomaterials for Selective Photocatalytic Mineralization of NOx Air Pollutants to Nitrate

Nitrogen oxide (NOx) gases emitted from vehicle exhausts are one of the major air pollutants in the dense cities in the King Saudi Arabia. There are extensive research efforts to reduce the NOx level in air. Photocatalysis have been introduced as a promising technology for NOx-abatement through utilizing solar energy. Photocatalysts such as TiO2 can act as a sensitizer for light-induced redox processes to produce an electron/hole pairs. The photo-generated holes are utilized for oxidation of NOx pollutants while the photo-generated electrons react with molecular oxygen to form oxygen active species, which are involved in the process. The main challenge for the application of this technology for NOx-abatement is the poor selectivity and the formation of more toxic products (e.g., nitrous acid (HONO) and nitrogen dioxide (NO2)). Another challenge is the fast recombination rate of the photogenerated holes and electrons and the low efficiency of the photocatalytic reactions. Therefore, the objective of this research project is to prepare advanced TiO2-based nanomaterials with modified surfaces to enhance their selectivity toward NOx photocatalytic mineralization to nitrate and to enhance their efficiency. Different methods will be employed for the synthesis of TiO2-based nanomaterials such as hydrothermal, sol-gel, hot-injection, micelle and inverse micelle methods. The synthesized materials will be characterized by different techniques such as scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS) and by electrochemical impedance spectroscopy (EIS). In addition, the electron paramagnetic resonance (EPR) spectroscopy will be employed to evaluate the reactivity of the different forms of catalysts toward the oxidation processes via radical intermediates. The photocatalytic activities of the synthesized materials will be assessed by NOx-abatement photocatalytic test according to the standard condition (ISO/DIS 22197-1). The percentage of NOx mineralization to nitrate will be calculated. The results will be analysed to find a relationship between the photocatalytic NOx-abatement selectivity and the physicochemical properties of the investigated photocatalysts. Finally, the most active photocatalyst(s) will be tested for air purification of model NOx system under solar light irradiation in order to assess the potential application of this technology for air purification on larger scale.