الفهرس 
English CoverOnly 14 pages are availabe for public view
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Abstract
Air pollution is becoming one of the most difficult environmental issues to deal with. As known, the polluted air includes various chemical compositions, including dust, toxic gases, green house gases, and metal salts. Among them, nitrogen oxides (NOx).NOx generation contains two majority routes. Natural emissions of NOx mainly come from the decomposition of organic substances in the soil or in the ocean, geologic activities (including volcano eruption, earthquakes, and others), and lightning, natural fires. Anthropogenic emissions of NOx mostly come from fossil fuel combustion processes, such as automobiles, aircraft, industrial and internal combustion processes. NOx have hazard for environment and humans as threats to human and animal health. Among of these hazardous is acid rain that causing climate change and ozone depletion. Two traditional routes were proposed by the scientists for removing NOx. The first approach is called selective non-catalytic reduction (SNCR) which utilized to improve coal combustion process through reducing the emission of NOx in thermal power industries. The other one is to purify the generated NOx via eliminating them from the flue gas, this method called selective catalytic reduction (SCR). These techniques need high cost and difficult specific environmental conditions, for example elevated temperature is required. Photocatalytic NOx removal approach gained great of attentions owing to its preferred advantages, including simple operation, low cost, high efficiency, and strong durability. Photocatalysts are widely used in fields such as energy conversion, organic synthesis and environmental photocatalytic processes. For practical applications of photocatalysts, it is important to develop highly active photocatalysts. To synthesize highly active photocatalytic materials, we have focused on two desirable properties; the photocatalyts should acquire large surface area and high crystalline. The former property should increase the amount of surface-adsorbed substrate(s) to enhance the capture of photogenerated electrons (e-) and positive holes (h+), and the latter, i.e., less defects acting as the recombination center, should suppress mutual e-–h+ recombination. In this protocol, TiO2 nanoparticles and modified TiO2 with Ag or Pt dopant were developed through photodeposition method. The as-prepared photocatalysts, TiO2, Ag/TiO2 and Pt/TiO2 were characterized using SEM, EDX, XRD, UV-Vis-DRS and FT-IR. Upon irradiation of visible light, the photocatalysts were participated in the oxidation-reduction (redox) reactions for NOx degradation through generation of electrons and holes in the conduction and valence bands, respectively. It was investigated that the conversion of NOx was 34.3% to 78.3% for Ag/TiO2, and the conversion of NOx was 35.2% to 78.5% for Pt/TiO2 under visible light irradiation conditions at room temperature. The used nano
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photocatalysts in this approach are characterized by their chemical stability, non-toxicity and relatively low cost which tends this approach will be more efficient and economic than traditional methods. Possible mechanism for the catalytic removal of NOx gases has been proposed depends on the photogeneration of superoxide’s and hydroxyl ions that can degradate NOx gases.