The role of oxygen vacancies on SnO2 in improving formaldehyde competitive adsorption: A DFT study with an experimental verification

The synthesis of metal oxides enriched with oxygen vacancies is beneficial for improving the gas-sensing properties of metal-oxide-based chemoresistive sensors. Density functional theory (DFT) calculations were performed to investigate the mechanism of adsorption of formaldehyde and acetone vapors on oxygen-vacancy-enriched SnO2. The ambient humidity and oxygen pressure were also considered in the calculations. The results indicated that oxygen vacancies play an important role in formaldehyde adsorption. The adsorption energy of formaldehyde on the reduced (1 1 0) surface was four times higher than that on the stoichiometric (1 1 0) surface, which was in turn, much higher than that of acetone. The presence of water molecules weakened the affinity of the adsorbed species for the SnO2 surface; however, the inhibition capacity varied. The formaldehyde molecules combined with the oxygen atom in the hydroxyl group to form dioxymethylene during adsorption, which mitigates the weakening effect. Oxygen-vacancy-enriched SnO2 was prepared to verify the validity of the DFT calculations.