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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.

The adsorption of benzotriazole and Cl on low Miller index surfaces of copper and under-coordinated defects thereon was characterized using density functional theory calculations; the former is an outstanding corrosion inhibitor and the latter a corrosion promoter. We find that adsorption bonding of intact benzotriazole (BTAH), dehydrogenated benzotriazole (BTA⊙), and Cl becomes stronger as the coordination number of surface Cu atoms involved in the adsorption site decreases, whereas the adsorption energy of Hconsidered as a side-product of BTAH dehydrogenationis rather insensitive to surface geometry. The Cl binds the strongest, and the binding energy ranges from −3.3 eV on Cu(111) to −3.9 eV on very low-coordinated defects, and BTA⊙binds somewhat weaker, from −2.8 to −3.8 eV, whereas BTAH binds considerably weaker, from −0.6 to −1.3 eV. The bonding enhancement due to reduced coordination of surface Cu atoms is hence the strongest for BTA⊙, which indicates its ability to passivate the reactive under-coordinated surface sites. This bonding enhancement is also a principal reason for the formation of organometallic complexes of BTA⊙on flat facets, such as the BTA–Cu–BTA complex or [BTA–Cu]npolymer. The role of solvent effects for the adsorption of considered species was also addressed, and approximate calculations reveal that the aqueous-phase adsorption of deprotonated BTA–is more exothermic than that of Cl–, mainly because the chloride anion is smaller and solvates considerably stronger in water than the BTA–.

The influence of the benzotriazole (BTAH) inhibitor on the thickness of the oxide layer formed on Cu immersed in 3% NaCl solution was studied with angle-resolved X-ray photoelectron spectroscopy. The X-ray-induced Auger spectra were reconstructed with the Monte Carlo algorithm using the spectra of the basic constituents [Cu(I)BTA, , and Cu] formed on the surface. The relative contributions of the basic constituents to the composite spectra measured at different emission angles were then used to estimate the thickness of the oxide layer. The results show that the presence of BTAH substantially reduces the thickness of the oxide layer formed on Cu in chloride media. The average thickness of the layer below the Cu(I)BTA layer is estimated to be , whereas the thickness of the noninhibited sample is .

The dissociative adsorption of chlorine on a perfect Cu(111) surface has been studied and characterized by means of extensive density functional theory calculations. A few properties of the bulk chlorides CuCl and CuCl2are also reported, because they may be viewed as a limiting case for Cl adsorption. Calculations predict that the chemisorption energy of Cl at low coverage is about −1.9 eV and remains so up to the coverage of 1/3 ML due to a good screening of metal electrons. Upon further increase of coverage, its magnitude decreases. It is further found that the substitutional adsorption mode is unstable, except at very large coverage (3/4 ML), where the mixed on-surface + substitutional structure is the most stable. The diagram of the adsorption free energy as a function of chlorine chemical potential reveals that the on-surface (√3 × √3)R30° adsorption phase is thermodynamically the most stable over a very broad range of Cl chemical potentials. The analysis of electronic structure points out that although the Cl adatoms are negatively charged, which results in an increase of the work function, the Cl−Cu interaction is not purely ionic but is to some extend also covalent, as witnessed by the formation of bonding and antibonding states. Results reveal that several Cl adsorption properties are almost unchanged up to the coverage of 1/3 ML, and at larger coverage, several new characteristics appear, such as occupation of nonoptimal surface sites, reduction of adatom net charge, and more covalent nature of the adsorbate−substrate interaction.

The influence of the benzotriazole (BTAH) inhibitor on the thickness of the Cu2Ooxide layer formed on Cu immersed in 3% NaCl solution was studied with angle-resolved X-ray photoelectron spectroscopy. The X-ray-induced Auger CuL3M4,5M4,5spectra were reconstructed with the Monte Carlo algorithm using the spectra of the basic constituents [Cu(I)BTA, Cu2O, and Cu] formed on the surface. The relative contributions of the basic constituents to the composite CuL3M4,5M4,5spectra measured at different emission angles were then used to estimate the thickness of the Cu2Ooxide layer. The results show that the presence of BTAH substantially reduces the thickness of the Cu2Ooxide layer formed on Cu in chloride media. The average thickness of the Cu2Olayer below the Cu(I)BTA layer is estimated to be 1.3±0.2nm, whereas the Cu2Othickness of the noninhibited sample is 2.2±0.3nm.