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Abstract
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The adsorption behaviors of SOx molecules on the pristine and N-doped ZnO
nanoparticles were investigated by using density functional theory calculations (DFT). The
results suggest improved adsorption ability for N-doped nanoparticles over undoped ones.
Various adsorption geometries and sites were considered in detail. In all adsorption sites, the
SOx molecule tends to form a bridge geometry with ZnO nanoparticle, giving rise to multiple
contacting points between the nanoparticle and SO x molecule. SOx adsorption on the N-doped
ZnO nanoparticle is found to be more favorable in energy than the adsorption on the undoped
one, suggesting that the N-doped nanoparticles have higher sensing capability than the pristine
ones. After the adsorption, the S-O bonds of the adsorbed SOx molecule were stretched, which
can be attributed to the transfer of electron density from the S-O bonds to the newly formed
bonds between the ZnO and SOx molecule. The charge analysis based on natural bond orbital
(NBO) method reveals a considerable charge transfer from the adsorbed SO x molecule to the
ZnO nanoparticle, indicating donor property of SO x molecules during the adsorption process.
By analyzing projected density of states, it was found that chemical bonds were formed
between the interacting atoms at the interface region. The results also indicate the electronic
densities in the highest occupied molecular orbitals (HOMOs) were mainly distributed over the
SO x molecules, whereas the lowest unoccupied molecular orbitals (LUMOs) were dominant at
the ZnO nanoparticle. Our DFT calculations shed light on the improved adsorption behaviors
of N-doped nanoparticles as innovative gas sensors for SOx detection in the environment.
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