Abstract
Today's WO3-based gas sensors have received a lot of attention, because of important role as a sensitive layer for detection of the small quantities of NOx. In this research, a theoretical study has been done on the sensing properties of different cyclic nanoclusters of (WO3)n (n = 2–6) for NOx (x = 1,2) gases. Based on the calculated adsorption energies by B3LYP and X3LYP functionals, from the different orientations of NOx molecule on the tungsten oxide clusters, O–N⋯W was preferred. Different sizes of the mentioned clusters have been analyzed and W2O6 cluster was chosen as the best candidate for NOx detection from the energy viewpoint. Using the concepts of the chemical hardness and electronic charge transfer, some correlations between the energy of adsorption and interaction energy have been established. These analyses confirmed that the adsorption energy will be boosted with charge transfer enhancement. However, the chemical hardness relationship is reversed. Finally, obtained results from the natural bond orbital and electronic density of states analysis confirmed the electronic charge transfer from the adsorbates to WO3 clusters and Fermi level shifting after adsorption, respectively. The last parameter confirms that the cyclic clusters of tungsten oxide can be used as NOx gas sensors.
Highlights
Semiconducting metal oxide sensors are one of the most studied groups of the chemical sensors which have been designed to react with gases [1]
Natural bond orbital (NBO) analysis which is suggested by Reed et al [28, 29] was carried out to explore the distribution of the electrons into atomic and molecular orbitals
The results showed that the adsorption energy depends on the size of the cluster
Summary
Semiconducting metal oxide sensors are one of the most studied groups of the chemical sensors which have been designed to react with gases [1]. WO3 based mixed oxides such as WO3-Ti [10], WO3-Pd, Pt, or Au [11], WO3-In2O3 [12], and WO3-Bi2O3 [13] have been investigated for their sensing characteristics These mixed oxides have been especially used in fabricating selective and sensitive NOx gas sensors. The theoretical works which have been done so far are based on the standard DFT methods which seriously underestimate the semiconductor band gap. This problem can be improved by using DFT in combination with the hybrid functionals which provide. Knowledge of the quantum reactivity indices and their role on the sensing properties of metal oxides is important to have an insight into the adsorption process and factors involved
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