Three corrosion inhibitors for copper-3-amino-1,2,4-triazole (ATA), benzotriazole (BTAH), and 1-hydroxybenzotriazole (BTAOH)-were investigated by corrosion experiments and atomistic computer simulations. The trend of corrosion inhibition effectiveness of the three inhibitors on copper in near-neutral chloride solution is determined experimentally as BTAH ≳ ATA ≫ BTAOH. A careful analysis of the results of computer simulations based on density functional theory allowed to pinpoint the superior inhibiting action of BTAH and ATA as a result of their ability to form strong N-Cu chemical bonds in deprotonated form. While these bonds are not as strong as the Cl-Cu bonds, the presence of solvent favors the adsorption of inhibitor molecules onto the surface due to stronger solvation of the Cl(-) anions. Moreover, benzotriazole displays the largest affinity among the three inhibitors to form intermolecular aggregates, such as [BTA-Cu](n) polymeric complex. This is another factor contributing to the stability of the protective inhibitor film on the surface, thus making benzotriazole an outstanding corrosion inhibitor for copper. These findings cannot be anticipated on the basis of inhibitors' molecular electronic properties alone, thus emphasizing the importance of a rigorous modeling of the interactions between the components of the corrosion system in corrosion inhibition studies.

A low-coverage gas-phase adsorption of three corrosion inhibitors-3-amino-1,2,4-triazole (ATA), benzotriazole (BTAH), and 1-hydroxybenzotriazole (BTAOH)-on perfect Cu(111) surface has been studied and characterized using density functional theory calculations. We find that the molecules in neutral form chemisorb weakly to the perfect surface in an upright geometry. The strength of the chemisorption increases in the order BTAH < BTAOH < ATA with adsorption energies of -0.40, -0.53, and -0.60 eV, respectively. The molecules bond to the surface with triazole nitrogen atoms and also through X-H···Metal hydrogen bonds (X = N or O). In addition to chemisorption, BTAH and BTAOH can also physisorb with the molecular plane being nearly parallel to the surface and the energies of the physisorption are -0.72 and -0.97 eV, respectively, hence being more exothermic than the corresponding chemisorption energies. On the other hand, the molecules in dehydrogenated form chemisorb strongly to the surface and the strength of the chemisorption increases in the order BTAO· < ATA· < BTA· with the adsorption energies of -1.65, -2.22, and -2.78 eV, respectively. This order is compatible with the trend of experimentally observed corrosion inhibition effectiveness on copper in near-neutral chloride solutions. Although the calculations are performed at the metal/vacuum interface, they provide enough insight to rationalize why in some experiments the BTAH was observed to be adsorbed with an upright geometry and in the others with parallel geometry.

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 CuCl2 are 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 adsorption of benzotriazole--an outstanding corrosion inhibitor for copper--on Cu(111), Cu(100), Cu(110), and low coordinated defects thereon has been studied and characterized using density functional theory (DFT) calculations. We find that benzotriazole can either chemisorb in an upright geometry or physisorb with the molecular plane being nearly parallel to the surface. While the magnitude of chemisorption energy increases as passing from densely packed Cu(111) to more open surfaces and low coordinated defects, the physisorption energy is instead rather similar on all three low Miller index surfaces. It is pointed out that due to a large dipole moment of benzotriazole the dipole-dipole interactions are rather important. For perpendicular chemisorption modes the lateral repulsion is very long ranged, extending up to the nearest-neighbor distance of about 60 bohrs, whereas for parallel adsorption modes the lateral interactions are far less pronounced and the molecules experience a weak attraction at distances ≲25 bohrs. The chemisorption energies were therefore extrapolated to zero coverage by a recently developed scheme and the resulting values are -0.60, -0.73, and -0.92 eV for Cu(111), Cu(100), and Cu(110), respectively, whereas the zero-coverage physisorption energy is about -0.7 eV irrespective of the surface plane. While the more densely packed surfaces are not reactive enough to interact with the molecular π-system, the reactivity of Cu(110) appears to be at the onset of such interaction, resulting in a very stable parallel adsorption structure with an adsorption energy of -1.3 eV that is ascribed as an apparent chemisorption+physisorption mode.

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] n polymer. 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 − .