An In-Situ EC-STM Study and DFT Modeling of the Adsorption of Glycerol on Cu(111) in NaOH Solution

International audienceOrganic 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 level. 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 (EC-STM) 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 to stabilize the glycerol film. This implies that interactions between glycerol molecules play a non-negligible effect in the growth process of such an organic film, allowing the formation of organic layers in the absence of strong interfacial interactions

Effect of van der Waals corrections on DFT-computed metallic surface properties

State-of-the-art van der Waals (vdW) corrected density functional theory (DFT) is routinely used to overcome the failure of standard DFT in the description of molecule/surface long range interactions. However, the systematic use of dispersion forces to model metallic surfaces could lead to less accurate results than the standard DFT and the effect of these corrections on the metal properties should be properly evaluated. In this framework, the behavior of two widely used vdW corrected DFT methods (DFT-D2 andvdW–DF/optB86b) has been evaluated on six metals, i.e. Al, Cu, Au, Ni, Co and Fe, with respect to standardGGA–DFT and experiments. Regarding bulk properties, general trends are found for the lattice parameter, cohesive energy and magnetic moment variations when thevdW correction is introduced. Surface energies, work functions and interlayer distances of closed packed surfaces, Al(111), Cu(111), Au(111) and magnetic Ni(111), Co(0001) and Fe(110), are also strongly affected by the dispersion forces. These modifications suggest a systematic verification of the surface properties when a dispersion correction is included

Corrosion protection of Al(111) by 8-hydroxyquinoline: a comprehensive DFT study

8-Hydroxyquinoline (8HQ) is a new green corrosion inhibitor. DFT-D calculations are performed to investigate the adsorption of 8HQ and derivatives on the Al(111) surface from low to high coverage. From θ = 0.20 to 0.66, the adsorption energies are −1.12, −2.41, −1.66 and −3.44 eV per molecule for 8HQ, and its tautomer, its hydrogenated and its dehydrogenated species, independently of the coverage. In contrast, the geometry of the adsorbates changes between coverage up to 0.66 and the full monolayer (θ = 1). The creation of a dipole at the molecule/metal interface reduces the work function of aluminum. To further evaluate the modification of the reactivity of the surface, adsorption of O2 on the Al(111) surface covered by the organic layer is investigated. O2 dissociation takes place for θ = 0.66. When the Al surface is fully covered (θ = 1), the reduction of O2 and the oxidation of Al atoms do not occur

Theoretical studies of green corrosion inhibitors : adsorption of the 8-hydroxyquinoline on aluminum surfaces

Les composés à base de chrome hexavalent sont industriellement utilisés pour inhiber la corrosion des alliages d'aluminium. Ils sont reconnus comme étant des inhibiteurs de corrosion très efficaces et permettent de renforcer les propriétés inhibitrices de la couche d'oxyde formée naturellement sur la surface en présence d'oxygène dans un environnement favorable. Cependant ces composés sont toxiques et cancérigènes. Ils doivent être éliminés (directives européennes) et remplacés par de nouveaux inhibiteurs de corrosion aussi efficaces mais respectueux de l'environnement. Certaines molécules organiques, biodégradables et non toxiques, pourraient jouer ce rôle. De nombreux travaux expérimentaux ont notamment démontré l'efficacité de la molécule de 8-hydroxyquinoléine (8HQ) pour améliorer la résistance à la corrosion de l'aluminium pur et de l'alliage 2024. Néanmoins, le mécanisme de l'inhibition de la corrosion à l'échelle atomique par cette molécule restait inconnu. Dans ces travaux de thèse, nous avons cherché, à l'aide de calculs de physico-chimie quantique, à identifier des facteurs favorables aux processus d'inhibition. Les propriétés d'inhibition de la corrosion sont directement liées au mécanisme d'interaction et aux phénomènes d'adsorption de ces molécules sur la surface du substrat. Nous avons ainsi étudié l'interaction de la molécule 8HQ et ses dérivés sur une surface Al(111). Les taux de recouvrement choisis ont permis de simuler divers cas, de l'adsorption d'une molécule isolée sur la surface à la formation de couches compactes sur le substrat. Outre la détermination des topologies d'adsorption et des énergies associées, nous avons réussi à déterminer la nature et la force des interactions molécules/substrat, notamment par l'étude de la structure électronique à l'interface hybride inhibiteur/métal. Quelle que soit la forme chimique de la 8-HQ (forme native, tautomère, espèces hydrogénée ou déshydrogénée) nous avons démontré que la couche organique adsorbée sur le métal est stable et fortement chimisorbée. Elle peut former une barrière à la pénétration d'agents agressifs sur la surface du substrat et limiter la réaction cathodique de réduction de l'oxygène. Les résultats obtenus contribuent à une meilleure connaissance des mécanismes d'inhibition de la corrosion de l'aluminium pur et aident à la recherche de nouvelles molécules qui pourraient assurer une protection avec une efficacité optimale.Chromates are currently used in the aeronautic industry to inhibit corrosion of aluminum alloys. They are known as very effective. However, these compounds are toxic and carcinogenic. They must be replaced by new efficient environmentally friendly corrosion inhibitors. Organic species that are biodegradable and non-toxic molecules could play this role. Several experimental studies demonstrated the efficiency of the 8-hydroxyquinoline molecule (8-HQ) to improve the corrosion resistance of pure aluminum and of 2024 aluminum alloy. However, the inhibition mechanism by the 8-HQ molecule is not totally understood, particularly at the atomic scale. In this PhD work, we tried, thank to DFT calculations, to identify factors that could be favorable to the inhibition processes. From a general point of view, the corrosion inhibition is directly related to the interaction mechanism and adsorption process of the molecules on the substrate surface. We studied the interaction of the 8-HQ molecule and its derivatives on the Al (111) surface. Various adsorption concentrations on the Al surface, from a single molecule to the formation of compact monolayer were modeled. Besides the determination of adsorption topologies and energies, we have identified the nature and strength of the molecules/substrate interactions by analyzing the electronic structure modification at the inhibitor/metal interface. Whatever the chemical form of the 8-HQ (native form, tautomer, hydrogenated or dehydrogenated species), it was demonstrated that the organic layer adsorbed on the metal is stable and strongly chemisorbed. This layer forms a barrier which could prevent the aggressive species to reach the Al surface and limit the oxygen cathodic reduction. The results contribute to a better understanding of the pure Al inhibition mechanisms and help the search for more efficient inhibitive “green” molecules

Étude théorique d'inhibiteurs verts de corrosion : adsorption de la 8-hydroxyquinoléine sur surfaces d'aluminium

Chromates are currently used in the aeronautic industry to inhibit corrosion of aluminum alloys. They are known as very effective. However, these compounds are toxic and carcinogenic. They must be replaced by new efficient environmentally friendly corrosion inhibitors. Organic species that are biodegradable and non-toxic molecules could play this role. Several experimental studies demonstrated the efficiency of the 8-hydroxyquinoline molecule (8-HQ) to improve the corrosion resistance of pure aluminum and of 2024 aluminum alloy. However, the inhibition mechanism by the 8-HQ molecule is not totally understood, particularly at the atomic scale. In this PhD work, we tried, thank to DFT calculations, to identify factors that could be favorable to the inhibition processes. From a general point of view, the corrosion inhibition is directly related to the interaction mechanism and adsorption process of the molecules on the substrate surface. We studied the interaction of the 8-HQ molecule and its derivatives on the Al (111) surface. Various adsorption concentrations on the Al surface, from a single molecule to the formation of compact monolayer were modeled. Besides the determination of adsorption topologies and energies, we have identified the nature and strength of the molecules/substrate interactions by analyzing the electronic structure modification at the inhibitor/metal interface. Whatever the chemical form of the 8-HQ (native form, tautomer, hydrogenated or dehydrogenated species), it was demonstrated that the organic layer adsorbed on the metal is stable and strongly chemisorbed. This layer forms a barrier which could prevent the aggressive species to reach the Al surface and limit the oxygen cathodic reduction. The results contribute to a better understanding of the pure Al inhibition mechanisms and help the search for more efficient inhibitive “green” molecules.Les composés à base de chrome hexavalent sont industriellement utilisés pour inhiber la corrosion des alliages d'aluminium. Ils sont reconnus comme étant des inhibiteurs de corrosion très efficaces et permettent de renforcer les propriétés inhibitrices de la couche d'oxyde formée naturellement sur la surface en présence d'oxygène dans un environnement favorable. Cependant ces composés sont toxiques et cancérigènes. Ils doivent être éliminés (directives européennes) et remplacés par de nouveaux inhibiteurs de corrosion aussi efficaces mais respectueux de l'environnement. Certaines molécules organiques, biodégradables et non toxiques, pourraient jouer ce rôle. De nombreux travaux expérimentaux ont notamment démontré l'efficacité de la molécule de 8-hydroxyquinoléine (8HQ) pour améliorer la résistance à la corrosion de l'aluminium pur et de l'alliage 2024. Néanmoins, le mécanisme de l'inhibition de la corrosion à l'échelle atomique par cette molécule restait inconnu. Dans ces travaux de thèse, nous avons cherché, à l'aide de calculs de physico-chimie quantique, à identifier des facteurs favorables aux processus d'inhibition. Les propriétés d'inhibition de la corrosion sont directement liées au mécanisme d'interaction et aux phénomènes d'adsorption de ces molécules sur la surface du substrat. Nous avons ainsi étudié l'interaction de la molécule 8HQ et ses dérivés sur une surface Al(111). Les taux de recouvrement choisis ont permis de simuler divers cas, de l'adsorption d'une molécule isolée sur la surface à la formation de couches compactes sur le substrat. Outre la détermination des topologies d'adsorption et des énergies associées, nous avons réussi à déterminer la nature et la force des interactions molécules/substrat, notamment par l'étude de la structure électronique à l'interface hybride inhibiteur/métal. Quelle que soit la forme chimique de la 8-HQ (forme native, tautomère, espèces hydrogénée ou déshydrogénée) nous avons démontré que la couche organique adsorbée sur le métal est stable et fortement chimisorbée. Elle peut former une barrière à la pénétration d'agents agressifs sur la surface du substrat et limiter la réaction cathodique de réduction de l'oxygène. Les résultats obtenus contribuent à une meilleure connaissance des mécanismes d'inhibition de la corrosion de l'aluminium pur et aident à la recherche de nouvelles molécules qui pourraient assurer une protection avec une efficacité optimale

Corrosion inhibition at emergent grain boundaries studied by DFT for 2-mercaptobenzothiazole on bi-crystalline copper

Abstract Inhibition of the initiation of intergranular corrosion was modeled at the atomic scale for 2-mercaptobenzothiazole (MBT) adsorbed on a (110)-oriented copper bi-crystal exposing an emergent Σ9 coincident site lattice (CSL) grain boundary (GB) using dispersion-corrected density functional theory (DFT-D). At both isolated molecule and full, dense monolayer coverages, the molecule adsorbed on the grain and GB sites stands perpendicular or tilted with no parallel orientation to the surface being favored. Chemical bonding of the thione and thiolate conformers involves both S atoms or the exocyclic S and N atoms, respectively. The full, dense monolayer is formed with a net gain in energy per surface area, but at the cost of a significant molecule deformation. It significantly enhances the Cu vacancy formation energy at the grain and GB sites, revealing that MBT also inhibits Cu dissolution for the more susceptible GBs with efficiency depending on atomic density of GB emergence

Capture of Iodine Species in MIL-53(Al), MIL-120(Al), and HKUST-1(Cu) Periodic DFT and Ab-Initio Molecular Dynamics Studies

International audienceThe potential use of three metal-organic frameworks (MIL-53(Al), MIL-120(Al) and HKUST-1(Cu)) to adsorb iodine species (I2 and 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 I2 and ICH3 are 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 (I2 and ICH3) and MOF structures are analyzed and the important role of van der Waals interactions in these materials is highlighted. © 2017 American Chemical Society

Adsorption of the Complex on the TiO2(110) surface in presence of water : Ab initio molecular dynamics studies

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DFT studies of the bonding mechanism of 8-hydroxyquinoline and derivatives on the (111) aluminum surface

International audienceThe 8-hydroxyquinoline (8-HQ) molecule is an efficient corrosion inhibitor for aluminum and is also used in organic electronic devices. In this paper, the adsorption modes of 8-HQ and its derivatives (tautomer, dehydrogenated and hydrogenated species) on the Al(111) surface are characterized using dispersion corrected density functional theory calculations. The 8-HQ molecule is physisorbed and is chemisorbed on the aluminum surface with similar adsorption energy (-0.86 eV to -1.11 eV) and these adsorption modes are stabilized by vdW interactions. The binding of the dehydrogenated species is the strongest one (adsorption energy of -3.27 eV to -3.45 eV), followed by the tautomer molecule (-2.16 eV to -2.39 eV) and the hydrogenated molecule (-1.71 eV) that bind weaker. In all the chemisorbed configurations there is a strong electronic transfer from the Al substrate to the adsorbate (0.72 e to 2.16 e). The adsorbate is strongly distorted and its deformation energy is high (0.55 eV to 2.77 eV). The analysis of the projected density of states onto the orbitals of the molecule and the electronic density variation upon adsorption (Dr) between the molecule and the surface account for covalent bonding