Investigation of the adsorption mechanism of formaldehyde on pure and Pt- doped rutile SnO2 (110) surfaces: a theoretical analysis via first principles study

Abstract

This work presents an extensive study for analysing the adsorption mechanism of formaldehyde on pure and Pt-doped rutile SnO2 (110) surfaces via Density Functional Theory (DFT) method. Out of the two suitable surface sites for Pt-doping, namely, Sn5c and Sn6c, the latter was found to be more suitable for Pt-doping. Three formaldehyde configurations were considered, η1(O)-straight, η1(O)-tilted and η2(O,C)-tilted. It was found that after Pt-substitution, the adsorption energies for η1(O)-tilted and η2(O,C)-tilted formaldehyde geometries were improved. This improvement could be due to strengthened interaction between formaldehyde and Sn5c sites after doping, and also due to the surface coverage induced by the tilt angle of the gas molecule w.r.t the surface. Also, the overall adsorption energy values were better for the tilted configurations rather than the straight geometry. Bader charge analysis results show the presence of both chemisorption as well as physisorption for tilted formaldehyde geometry, whereas only chemisorption has been observed in case of straight orientation. Charge density difference (CDD) plots visually verified the above stated results. Total density of states show the injection of additional electronic states near zero energy (Fermi energy) level after Pt-doping and an additional peak upon introduction of the gas molecule.