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Organic coatings are often required for the protection of metals against environmental degradation. Despite their extensive use, only limited information is available on the initial stages of adsorption and formation of protective films, especially at the molecular and atomic levels. As a model system for coating formation, this study investigates the adsorption of glycerol molecules on the single-crystalline Cu(111) surface. A combined electrochemical and scanning tunneling microscopy study in NaOH aqueous solution enabled following the adsorption process in detail, providing molecular information on the glycerol film structure. A potential-driven adsorption of glycerol was observed, suppressing the adsorption of hydroxyl molecules and copper oxidation. The adsorbed species assembled in a nearest neighbor arrangement fitting a (√3 × √3) R30° hexagonal structure with respect to the Cu(111) lattice. This experimentally observed configuration was confirmed by density functional theory (DFT) calculations. DFT modeling indicates that a mixed adsorption mode involving the two primary alcohol groups adsorbed at different z-positions relative to the surface is the most favorable. This mixed configuration enabled the formation of an extended network of hydrogen bonds that aids in stabilization of the glycerol film. This implies that interactions between glycerol molecules have a non-negligible effect on the growth process of such an organic film, allowing the formation of organic layers in the absence of strong interfacial interactions.

The potential use of three metal–organic frameworks (MIL-53(Al), MIL-120(Al) and HKUST-1(Cu)) to adsorb iodine species (I2and ICH3), which can be released during a severe nuclear accident, is investigated using periodic dispersion density functional theory for the first time. Competitive adsorption of iodine in the presence of water molecules is also characterized for the hydrophilic HKUST-1(Cu). In the first step, we have found that the absolute values of interaction energies of I2and ICH3are higher in the hydrated form of HKUST-1(Cu) than in the dehydrated one, which is of very high interest for iodine trapping. In a second stage, iodine species are strongly adsorbed in MIL-53(Al) than in MIL-120(Al) and HKUST-1(Cu) MOFs and therefore this material could potentially trap iodine compounds. Moreover, we study the influence of the functionalization of the MIL-53(Al) organic linkers on the adsorption behavior of iodine and it turns out that the substitutions does not present a significant effect for this purpose. The factors governing the interaction energies between iodine (I2and ICH3) and MOF structures are analyzed and the important role of van der Waals interactions in these materials is highlighted.

We address the mechanism by which organic layers on aluminum substrate hinder the penetration of Cl−toward the metal substrate. Localized corrosion by chlorides on Al and its alloys is a major problem, and organic molecules that form self-assembled monolayers on metal substrates may provide efficient corrosion protection. In one of our previous works, we established experimentally that long-chain n-alkyl carboxylic acids form protective layers against Cl−corrosion on Al substrates. In a different work, we identified, using implicit models of the organic layer and metal substrate, two essential effects by which organic layers hinder the penetration of Cl−ions toward the metal substrate. The first effect is due to the inferior solvation of ions in the organic layer compared to that in an aqueous solvent. The second effect is due to the electric field at the electrochemical interface, and the extent to which it affects the penetration of Cl−depends on the electrode potential and the thickness of the organic layer. Both effects are related to a low dielectric constant of the self-assembled monolayer. In the present study, we continue our investigation and explicitly model the organic monolayer and Al substrate using density-functional-theory calculations. To this end, we consider organic monolayers consisting of either dodecanoic- or hexanoic-acid molecules. Current calculations confirm the findings of the simplified implicit models, i.e. the energy barrier for the Cl−penetration increases with the thickness of the organic monolayer and with Cl−concentration in the monolayer. Furthermore, we propose a new mechanism by which Cl−penetrates the organic monolayer. Due to the considerably inferior solvation of Cl−in the organic layer compared to that in water, calculations suggest that it is energetically easier to locally “open” the organic monolayer by creating a hole large enough to accommodate water molecules and Cl−. The presence of water molecules ensures a stronger Cl−solvation and a better electrostatic screening between anions. While the energy barrier for the Cl−penetration via the local “opening” mechanism is suggested to be smaller than for the penetration of Cl−into dense homogeneous organic monolayer, it is still significant enough to pose a considerable kinetic barrier for the penetration of Cl−from the aqueous solution into the organic monolayer at room temperature.