Benzotriazole adsorption on Cu ₂O(111) surfaces: A first-principles study

The adsorption of benzotriazole (BTAH) on Cu ₂O(111) was investigated with use of first-principles density functional theory calculations. Two possible adsorption structures were considered for both one-quarter and full adsorption coverage. We found that BTAH strongly chemisorbs (1.2-1.5 eV) onto Cu ₂U(111) by forming a chemical bond with a surface copper atom through nitrogen sp ² lone pairs, and a hydrogen bond with a surface oxygen atom through a C-H or N-H proton. The chemical interaction between the surface copper site and the molecule is the combined effect of a strong lone-pair → hybrid Cu-d _z2sp _z σ-donation and a relatively weak d _yz → 6π* back-donation. Vibration calculations were carried out to predict the BTAH-Cu ₂O stretching frequencies for both adsorption structures. The calculated stretching frequency (381 and 428 cm ^-1) could overlap with the BTAH benzene-ring torsion band. An estimate for the BTAH-Cu vibrational frequency (226 and 223.4 cm ^-1 for two adsorption modes, respectively) is in good agreement with an experimentally observed Raman peak of 240 cm ^-1.