Photocatalytic oxidation of nitrogen oxides (NOx) using Ag- and Pt-doped TiO2 nanoparticles under visible light irradiation.

In this work, titanium dioxide nanoparticles (TiO2 NPs) and modified TiO2 NPs with silver (Ag) or platinum (Pt) dopant were developed through photodeposition method for the NOx conversion into nitric acid (HNO3) under visible light irradiation. The formed photocatalysts TiO2, Ag/TiO2, and Pt/TiO2 nanocomposites were characterized by utilizing TEM, SEM, energy-dispersive X-ray analysis (EDX), XRD, UV/visible diffuse reflectance spectroscopy (UV-Vis DRS), and FT-IR. It had been investigated that an enhancement within the conversion of NOx into HNO3 was increased from 34.3 to 78.3% for Ag/TiO2 and from 35.2 to 78.5% for Pt/TiO2 under visible light irradiation conditions at room temperature for less than 2 h. The photodegradation rate order of NOx under visible light irradiation is Pt/TiO2 ~ Ag/TiO2 > TiO2. A possible mechanism for the catalytic conversion of NOx gases has been proposed, which depends on the photogeneration of electrons and holes after the excitation of nanocatalysts under visible radiation that promoted superoxide and hydroxyl ions, which can depredate NOx gases. This approach of NOx photocatalytic conversion is characterized by its chemical stability, low cost, high efficiency, simple operation, and strong durability than traditional methods.