Formaldehyde Adsorption on the Anatase TiO₂(101) Surface: Experimental and Theoretical Investigation

Abstract

Formaldehyde (CH2O) adsorption on the anatase TiO2(101) surface was studied with a combination of experimental and theoretical methods. Scanning tunneling microscopy, noncontact atomic force microscopy, temperature-programmed desorption, and X-ray photoelectron spectroscopy were employed on the experimental side. Density functional theory was used to calculate formaldehyde adsorption configurations and energy barriers for transitions between them. At low coverages (<0.25 monolayer), CH2O binds via its oxygen atom to the surface 5-coordinated Ti atoms Ti5c (monodentate configuration). At higher coverages, many adsorption configurations with comparable adsorption energies coexist, including a bidentate configuration and paraformaldehyde chains. The adsorption energies of all possible adsorption configurations lie in the range from 0.6 to 0.8 eV. Upon annealing, all formaldehyde molecules desorb below room temperature; no other reaction products were detected.