First-principles study of formaldehyde adsorption on TiO ₂ rutile (110) and anatase (001) surfaces

This study investigated adsorption and reactions of formaldehyde (HCHO) on TiO ₂ rutile (110) and anatase (001) surfaces by first-principles calculation. The structure, vibrational frequencies, and electronic properties of the interaction system are studied to investigate the adsorption mechanisms of HCHO on TiO ₂ surfaces. It is found that HCHO can chemically adsorb on all surfaces to form into a dioxymethylene structure with O of HCHO bonding to a coordinatively unsaturated surface Ti atom (Ti _4C or Ti _5C) and C bonding to a surface O _2C. The anatase (001) surface is found to be more active in HCHO adsorption with lower adsorption energy and larger charge transfer. In addition, the (1 × 4) reconstructed anatase (001) surfaces are found to have higher adsorption ability and more stable surface properties than that on (1 × 1) unreconstructed ones. These findings indicate that the (001) surface holds the potential for the improvement of sensitivity to reductive HCHO gas, in which the (1 × 4) reconstructed surface may play an important role for further improving gas-sensing properties of TiO ₂-based sensors while keeping the stability of them. © 2012 American Chemical Society.