Formaldehyde on TiO2 anatase (1 0 1): A DFT study

The adsorptions of formaldehyde molecule on the stoichiometric anatase TiO2 (1 0 1) surface have been studied by first principles calculations. Four types of adsorption have been investigated at 0.25 ML coverage. Two of them are chemical adsorptions and the other two are physical adsorptions. For the chemical adsorptions, C, O atoms in the formaldehyde molecule form two bonds with the O2c/O3c and Ti5c on the anatase (1 0 1) surface. The CO bond in the formaldehyde molecule is elongated and a dioxymethylene structure forms in the two chemical adsorptions. The OTi5c interaction can be found in the two physical adsorptions and it is the only contacting point at the interface. No serious internal distortion in the formaldehyde molecule can be found in the physical adsorptions. The LDOS and the difference of the charge density are calculated to investigate the interface bonds of the adsorption. As the adsorption coverage increase, the molecules on the surface repel each other and weaken the adsorptions. For example, the chemical adsorption may become physical adsorption at high coverage.