Sub-stoichiometric WO2.9 for formaldehyde sensing and treatment: a first-principles study

Abstract

The on-line detection and treatment of atmospheric formaldehyde (HCHO) at real-time levels, especially in indoor environments, is becoming more and more important. Herein, by first principles calculations, a highly active sub-stoichiometric WO_2.9 (010) surface for HCHO sensing and treatment has been demonstrated. The exposed one-coordinated terminal O atoms (O_1c), two-coordinated bridge O atoms (O_2c) and five-coordinated W atoms (W_5c) at the surface are found to be active sites for HCHO adsorption. HCHO molecules can anchor on the WO_2.9 (010) surface through newly formed O_F–W_5c and/or C_F–O_1c/O_2c/W_5c bonds, forming ‘ridge-like’/’hobbyhorse-like’ or slantwise adsorption configurations. The absorbed HCHO molecules may exchange electrons with the WO_2.9 (010) surface and change the conductivity of the surface, which is the working mechanism of WO_2.9 based sensors. Furthermore, Cl-NEB results suggest that the absorbed HCHO molecules tend to dissociate under moderate excitation (for example, solar visible light) at room temperature due to the minimum energy barrier of only 0.54 eV. The HCHO dissociation results in an H adatom bond to a surface O_1c atom and a formate or formyl group chemisorbed to the surface with elongated O_F–W_5c and C_F–W_5c bonds, which means that O_F–W_5c and C_F–W_5c bonds are active and prone to breaking. These results demonstrate the potential of WO_2.9 in HCHO sensing and elimination.