The Effect of Surface Geometry of Copper on Dehydrogenation of Benzotriazole. Part II

Dehydrogenation of benzotriazole (BTAH)-an outstanding corrosion inhibitor for copper-on low Miller index surfaces of copper and under-coordinated defects thereon has been characterized using density functional theory calculations. The issue of dehydrogenation is of importance, because benzotriazole bonds strongly to copper surfaces-a requirement for successful competition with corrosive species-only in dehydrogenated (or deprotonated) form. The calculated dehydrogenation activation energy of weakly chemisorbed BTAH-oriented with the molecular plane perpendicular to the surface-is about 1.1 eV on Cu(111), whereas, on more open Cu(100) and step-edges, the activation energy decreases to values closely below 1.0 eV. On the other hand, dehydrogenation activation energies of physisorbed BTAH-oriented with the molecular plane parallel to the surface-are found to be considerably smaller; the smallest calculated value is 0.73 eV. We also find that dehydrogenation barriers decrease with increasing molecular coverage. The effect of aqueous solvent on dehydrogenation of adsorbed BTAH is also considered, and calculations suggest that, in some cases, water molecules may aid the dehydrogenation by reducing the activation energy. Our calculations, therefore, suggest that dehydrogenation of BTAH can be feasible on more open or defective surfaces of copper, whereas, on densely packed Cu(111), it is hindered, because there the desorption energy of about 0.6 eV is considerably smaller.