Trapping of CO, CO2, H2S, NH3, NO, NO2, and SO2 by polyoxometalate compound

Abstract

The forthcoming research includes the efficacy of polyoxometalate (POM) compound as an adsorbent for the following pollutant gases CO, CO2, H2S, NH3, NO, NO2, and SO2. The investigated complex was first optimized using TPSSh/LANL2DZ model chemistry to obtain the most stable geometry of the isolated and complex structures. After which the adsorption energy of the complex was ascertained in other to identify the complex with comparably stronger adsorption energy and the most stable complex. To understand the nature of intermolecular interactions occurring during the adsorption process, we carried out quantum theory of atoms in molecules (QTAIM) and natural bonding orbitals (NBO) calculations so as to carefully estimate the bond order of the studied complexes. It is very important to know the nature of conductivity of the complex being adsorbed as such this information is provided by the HOMO-LUMO energy gap. From energy gap considerations, there is increase as well as a corresponding decrease following the adsorption of each gas on polyoxometalate. The energy gap of the POM before adsorption was observed to be 0.602 eV, however upon adsorption of CO and CO2 it was observed to increase to 0.608 eV and 0.618 eV, with a difference of 0.006 eV and 0.016 eV. The increase in band gap was accompanied with a sharp decrease as H2S gas was adsorbed on POM with band gap of 0.122 eV a reduction of 0.496 eV from the band gap of CO2@POM, which indicate an increase in adsorption rate with a less stability of the adsorption process. The overall consideration of the adsorption energy and band gap shows that POM adsorbed NO, NH3 (NO@POM, NH3@POM) better since it had the highest adsorption energy; thus, NO and NH3 would be more efficiently detected by polyoxometalate molecule.