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Abstract
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The rapid progress of industrialization and urbanization in recent decades has caused an accumulation in industrial pollutants in the atmosphere, which in addition to creating serious threats to human health, causes environmental and climate problems such as the emission of greenhouse gases and toxic gases. Therefore, searching for new materials that can sense and adsorb these gases has attracted significant attentions. In this work, we studied the adsorption of three air pollutant molecules including CO2, SO2 and NH3 molecules on the N-doped ZnO surface (N-ZnO) using density functional theory (DFT) method as implemented in Vienna ab initio simulation package (VASP) [1]. To simulate the N-ZnO surface, two ZnO layer was cleaved from its bulk wurtzite structure with the hexagonal unit cell in (0001) direction [2]. The O-terminated surface was used to study the adsorption process. Then two O atoms have been replaced by N atoms and one O-vacancy has been created to balance the electronic structure. The results have been analyzed by estimating the adsorption energy, projected density of states (PDOS), charge transfer and charge density differences (CDD) for all molecule.
Based on the results, it is evident that the adsorption energies of CO2, SO2, and NH3 are −0.14 eV, −2.77 eV and −2.84 eV, respectively. These results suggest that the adsorption of NH3 and SO2 exhibits greater energetic favorability compared to CO2. In addition, the charge analyses reveal that charge transfer occurs from the N-ZnO surface to SO2 molecule, while it is occurred from NH3 molecule to the surface. However, the magnitude of charge transfer between surface and NH3 molecule is more than others and so the N-ZnO surface is much more sensitive to NH3 detection. Considering PDOS of interacted surface atoms and adsorbed molecules show the variations around the fermi level after adsorption that indicate the interaction between molecules and surface.
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