Hydrogen at symmetric tilt grain boundaries in aluminum: segregation energies and structural features.

Aluminum is envisioned to be an important material in future hydrogen-based energy systems. Here we report an ab initio investigation on the interactions between H-atoms and common grain boundaries (GBs) of fcc Al: Σ9, Σ5, Σ11 and Σ3. We found that upon segregation to the GBs, single H-atoms can cause displacement of Al-atoms. Increasing their concentration revealed large cooperative effects between H-atoms that favor the segregation when other H-atoms are bound at neighboring sites. This makes these GBs able to accommodate high concentrations of H-atoms with considerable segregation energies per atom. Structural analyses derived from Laguerre-Voronoi tessellations show that these GBs have many interstitial sites with higher symmetry than the bulk tetrahedral interstitial site. Many of those sites have also large volumes and higher coordination numbers than the bulk sites. These factors are the increased driving force for H-atom segregation at the studied GBs in Al when compared to other metals. These GBs can accommodate a higher concentration of H-atoms which indicates a likely uniform distribution of H-atoms at GBs in the real material. This suggests that attempting to mitigate hydrogen uptake solely by controlling the occurrence of certain GBs may not be the most efficient strategy for Al.

Interactions between glucosides of the tip of the S1 subunit of SARS-CoV-2 spike protein and dry and wet surfaces of CuO and Cu-A model for the surfaces of coinage metals.

Despite their importance there is little knowledge at the atomic scale on the interactions between fragments of SARS-CoV-2 and inorganic materials. Such knowledge is important to understand the survival of the virus at surfaces and for the development of antiviral materials. Here is reported a study of the interactions between glucoside monomers of the tip of the S1 subunit of SARS-CoV-2 spike protein with dry and wet surfaces of CuO and Cu, performed with dispersion corrected density functional theory-DFT. The three glucoside monomers that constitute the tip of S1: 6VSB, 6VXX and 6X6P, were adsorbed onto dry and wet CuO(111) and Cu(110) with different orientations and surface alignments. There are large differences-of up to 1.3 eV-in binding energies between these monomers and the surfaces. These differences depend on: the type of surface; if the surface is wet or dry; if the glucosidic O-atom points towards or away from the surfaces; and to a smaller extent on the surface alignment of the monomers. All monomers bind strongly to the surfaces via molecular adsorption that does not involve bond breaking in the monomers at this stage. 6VSB has the larger adsorption energies-that reach 2.2 eV-due to its larger dipole moment. Both materials bind the monomers more strongly when their surfaces are dry. At Cu(110) the bonds are on average 1 eV stronger when the surface is dry when compared to wet. The difference between dry and wet CuO(111) is smaller, in the order of 0.2 eV. Overall, it is here shown that the stability of the monomers of the tip of the spike protein of the virus is very different at different surfaces. For a given surface the larger binding energies in dry conditions could explain the differences in the surface stability of the spike protein depending on the presence of moisture.

Novel process for decontamination and additional valorization of steel making dust processing using two-step correlative leaching.

Recycling of steel making dusts often targets Zn removal. Other heavy metals such as Mo, W or Cr do not receive as much attention, and the decontamination of the dusts from these constituents is scarcely addressed in the literature. This study presents a novel approach of the selective separation of Mo from steel making dusts using alkaline solutions with low concentrations, before Zn removal using concentrated alkaline medium. Such an approach has never been reported before and can contribute to more efficient decontamination of the steel making dusts and will increase the value of recovered components since Mo can be significantly preconcentrated. Two samples originating from two steel producers were investigated. One sample contained 2.65% of Mo and 1.87% of Zn, and the second sample had 0.61% of Mo and 35.9% of Zn. Temperature was found to have a low impact on the leaching efficiency of Mo, while increased NaOH concentration promoted leaching of Zn. Excellent pre-concentration of Mo was achieved by using a S:L ratio of 1:3. Almost 5170 mg/L Mo, 1000 mg/L W, no Fe and only 2 mg/L Zn were present in the solution after leaching at 30 °C for 30 min. For the samples containing lower concentrations of Mo and high concentrations of Zn, the selectivity of the process was affected when using higher concentrations of NaOH. A final leachate containing 797 mg/L of Mo and only 11 mg/L Zn was obtained after leaching with 0.05 M NaOH. DFT computations showed that the 2D layered structures of MoO3 and WO3 are decisive factors that account for their high solubilites.

The first stages of oxide growth at the low index Al surfaces (100), (110), (111): clusters and stripes vs. homogeneous growth.

We performed a density functional theory (DFT) investigation of the mechanisms of oxide growth at Al(100), Al(110) and Al(111) up to 1 monolayer (ML) coverage of O-atoms with 0.125 ML increments. We found that the surface binding site preferences of O-atoms are largely affected by the presence of neighboring O-atoms. Based on this we constructed two oxide growth models: the formation of clusters that evolve to stripes with increasing coverage and the formation of a more homogeneous distribution of O-atoms. While the former model is characterized by a lower symmetry of distribution of O-atoms at the surfaces, the latter corresponds to higher symmetries. We found that the prevalence of each oxide growth mode depends on the coverage of O-atoms and that this dependency is different for each surface. For Al(100) and Al(110), up to coverages of 1 ML the oxide grows preferably via the formation of clusters that evolve to stripes with increasing coverage, while for Al(111) the stripes and clusters are the preferred growth mode for coverages up to 0.375 ML, beyond which the homogeneous growth mode is energetically favored. The calculated Al-O pair distribution functions show that the formation of clusters and stripes leads to shorter Al-O bond lengths when compared to the homogeneous growth. The oxides formed at Al(100) and Al(110) have Al-O bond lengths and geometries typical of the shorter bonds of α-alumina while at Al(111) the bond lengths are typical of γ-alumina and ß-alumina. These results suggest that for low coverages, the oxides formed at Al(100) and Al(110) are resemblant of defective α-alumina while the oxide formed at Al(111) is similar to less disordered γ-alumina and ß-alumina. For Al(111), the small energy difference between the growth of clusters and stripes and homogeneous growth does not exclude the coexistence of both growth modes; this could lead to the formation of a defective or amorphous oxide.

Adsorption of Hydrogen Sulfide, Hydrosulfide and Sulfide at Cu(110) - Polarizability and Cooperativity Effects. First Stages of Formation of a Sulfide Layer.

Understanding the surface site preference for single adsorbates, the interactions between adsorbates, how these interactions affect surface site specificity in adsorption and perturb the electronic states of surfaces is important for rationalizing the structure of interfaces and the growth of surface products. Herein, using density functional theory (DFT) calculations, we investigated the adsorption of H2 S, HS and, S onto Cu(110). The surface site specificity observed for single adsorbates can be largely affected by the presence of other adsorbates, especially S that can affect the adsorption of other species even at distances of 13 Å. The large supercell employed with a surface periodicity of (6×6) allowed us to safely use the Helmholtz method for the determination of the dipole of the surface-adsorbate complex at low adsorbate coverages. We found that the surface perturbation induced by S can be explained by the charge transfer model, H2 S leads to a perturbation of the surface that arises mostly from Pauli exclusion effects, whereas HS shows a mix of charge transfer and Pauli exclusion effects. These effects have a large contribution to the long range adsorbate-adsorbate interactions observed. Further support for the long range adsorbate-adsorbate interactions are the values of the adsorption energies of adsorbate pairs that are larger than the sum of the adsorption energies of the single adsorbates that constitute the pair. This happens even for large distances and thus goes beyond the H-bond contribution for the H-bond capable adsorbate pairs. Exploiting this knowledge we investigated two models for describing the first stages of growth of a layer of S-atoms at the surface: the formation of islands versus the formation of more homogeneous surface distributions of S-atoms. We found that for coverages lower than 0.5 ML the S-atoms prefer to cluster as islands that evolve to stripes along the [1 1‾ 0] direction with increasing coverage. At 0.5 ML a homogeneous distribution of S-atoms becomes more stable than the formation of stripes. For the coverage equivalent to 1 ML, the formation of two half-monolayers of S-atoms that disrupt the Cu-Cu bonds between the first and second layer is more favorable than the formation of 1 ML homogeneous coverage of S-atoms. Here the S-Cu bond distances and geometries are reminiscent of pyrite, covellite, and to some extent chalcocite. The small energy difference of ≈0.1 eV that exists between this structure and the formation of 1 ML suggests that in a real system at finite temperature both structures may coexist leading to a structure with even lower symmetry.

Synthesis of copper hydride (CuH) from CuCO3·Cu(OH)2 - a path to electrically conductive thin films of Cu.

The most common synthesis methods for copper hydride (CuH) employ hard ligands that lead to the formation of considerable amounts of metallic Cu as side-product. Here we explore a synthesis method for CuH(s) through the reaction of CuCO3·Cu(OH)2(s) with hypophosphorous acid (H3PO2) in solution, via the formation of the intermediate Cu(H2PO2)2(aq) complex. The reaction products were characterized with XRD, FTIR and SEM at different reaction times, and the kinetics of the transformation of Cu(H2PO2)2(aq) to CuH(s) were followed with NMR and are discussed. We show that our synthesis method provides a simple way for obtaining large amounts of CuH(s) even when the synthesis is performed in air. Compared to the classic Würtz method, where CuSO4 is used as an initial source of Cu2+, our synthesis produces CuH particles with less metallic Cu side-product. We attribute this to the fact that our reaction medium is free from the hard SO42- ligand that can disproportionate Cu(i). We discuss a mechanism for the reaction based on the known reactivity of the reagents and intermediates involved. We explored the possibility of using CuH(s) for making electrically conductive films. Tests that employed water-dispersed CuH particles show that this compound can be reduced with H3PO2 leading to electrically conductive thin films of Cu. These films were made on regular office paper and were found to be Ohmic conductors even after several weeks of exposure to ambient conditions. The fact that the synthesis reported here produces large amounts of CuH particles in aqueous media, with very little impurities, and the fact that these can then be converted to a stable electrically conductive film can open up new applications for CuH such as for printing electrically conductive films or manufacturing surface coatings.

Molecular and dissociative adsorption of water and hydrogen sulfide at perfect and defective Cu(110) surfaces.

We performed a density functional theory (DFT) investigation of the molecular and dissociative adsorption of H2O and H2S at perfect and defective Cu(110) surfaces described using supercells with c(6 × 6) periodicity. The defective surface consists of a terrace surrounded by pits. We found considerable differences in adsorption modes and energies for H2O and H2S. At the defective Cu(110) surface, monomers of H2O and H2S preferentially adsorb at the terrace site and molecular adsorption of H2O is significantly more favorable than that of H2S. For dissociative adsorption however, the sulfur species are considerably more stable than the oxygen species. For monolayer (ML) coverages, there are small differences in the molecular adsorption energies for H2O and H2S. However, for the formation of 1 ML of HO and 1 ML of HS from 1 ML of H2O and 1 ML of H2S, respectively, with the release of H2(g), the differences are very large. The formation of 1 ML HO at the perfect Cu(110) surface is endoergic, while at the defective Cu(110) surface it is exoergic by -0.6 eV. For high coverages, H2S forms stacked half-monolayers that interact with each other via a complex hydrogen bond network with a strength per H2S molecule of -0.140 eV per H2S and -0.120 eV per H2S for H2S located in the underlayer and overlayer, respectively. The large distances between hydrogen bonded H2S molecules explain the preference for the formation of the two stacked half-monolayers of H2S instead of a single monolayer as it happens with H2O. Additionally, the formation of 1 ML of HS does not occur because of the spontaneous splitting of some H-S bonds resulting in surface bound HS and S and H2S molecules. Extensive surface reconstruction and relaxation accompanies adsorption of the sulfur adsorbates. Such reconstructions with outwards pull of Cu atoms can be at the origin of the weak adhesion of sulfide films that explains the release of CuS particles from copper sulfide films at copper surfaces. Overall, the surface defects here investigated induce non-linear effects in the molecular and dissociative adsorption energies of different O and S adsorbates.

Gamma radiation induces hydrogen absorption by copper in water.

One of the most intricate issues of nuclear power is the long-term safety of repositories for radioactive waste. These repositories can have an impact on future generations for a period of time orders of magnitude longer than any known civilization. Several countries have considered copper as an outer corrosion barrier for canisters containing spent nuclear fuel. Among the many processes that must be considered in the safety assessments, radiation induced processes constitute a key-component. Here we show that copper metal immersed in water uptakes considerable amounts of hydrogen when exposed to γ-radiation. Additionally we show that the amount of hydrogen absorbed by copper depends on the total dose of radiation. At a dose of 69 kGy the uptake of hydrogen by metallic copper is 7 orders of magnitude higher than when the absorption is driven by H2(g) at a pressure of 1 atm in a non-irradiated dry system. Moreover, irradiation of copper in water causes corrosion of the metal and the formation of a variety of surface cavities, nanoparticle deposits, and islands of needle-shaped crystals. Hence, radiation enhanced uptake of hydrogen by spent nuclear fuel encapsulating materials should be taken into account in the safety assessments of nuclear waste repositories.

Surface chemistry of oxygen on aluminum--Performance of the density functionals: PBE, PBE0, M06, and M06-L.

We investigated the performance of the density functional theory (DFT) functionals PBE, PBE0, M06, and M06-L for describing the molecular and dissociative adsorption of O2 onto pure and doped Al(111) surfaces. Adsorption of O2 was studied at the perfect Al(111) surface and compared with the case where an additional Al atom was present as an adatom. Additionally, we studied how these functionals perform when different dopants are present at the Al(111) surface in two distinct geometries: as an adatom or as a substitutional atom replacing an Al atom. The performance of the different functionals is greatly affected by the surface geometry. The inclusion of Hartree-Fock exchange in the functional leads to slight differences in adsorption energies for molecular adsorption of O2 . These differences become very pronounced for dissociative adsorption, with the hybrids PBE0 and M06 predicting more exergonic adsorption than PBE and M06-L. Furthermore, PBE0 and M06 predicted trends in adsorption energies for defective and perfect surfaces which are in line with the experimental knowledge of the effects of surface defects in adsorption energies. The predictions of the non-hybrids PBE and M06-L point in the opposite direction. The analysis of the contributions of the van der Waals (vdW) forces to the adsorption energies reveals that the PBE and PBE0 functionals have similar difficulties in describing vdW interactions for molecular adsorption of O2 while the M06 functional can give a description of these forces with an accuracy which is at least similar to that of the correction of the D3 type.

Bond network topology and antiferroelectric order in cuprice CuOH.

Using density functional theory (DFT) and a graph theory based approach, we investigated the topology of bond network in CuOH(s) (cuprice) considering only symmetry-distinct structures. In parallel, we conducted the synthesis and X-ray diffraction characterization of the compound and used the combined theoretical-experimental effort to validate the lowest energy structure obtained with DFT. The ground-state structure of CuOH(s) consists of compact trilayers of CuOH connected to each other via hydrogen bonds, where the inner layer of each trilayer is composed entirely of Cu atoms. Each trilayer is a dense fabric made of two interlocked arrays of polymer [CuOH]n chains. This structure corresponds to an antiferroelectric configuration where the dipole moments of CuOH molecules belonging to adjacent arrays are antiparallel and are arranged in the same way as the water molecules in ice-VIII. It is shown that a collective electrostatic interaction is the main driving force for the cation ordering while the local atomic configuration is maintained. These findings and the possibility of synthesizing exfoliated two-dimensional cuprice are important for some technological applications.

Oxygen adsorption onto pure and doped Al surfaces--the role of surface dopants.

Using density functional theory (DFT) with the PBE0 density functional we investigated the role of surface dopants in the molecular and dissociative adsorption of O2 onto Al clusters of types Al50, Al50Alad, Al50X and Al49X, where X represents a dopant atom of the following elements Si, Mg, Cu, Sc, Zr, and Ti. Each dopant atom was placed on the Al(111) surface as an adatom or as a substitutional atom, in the last case replacing a surface Al atom. We found that for the same dopant geometry, the closer is the ionization energy of the dopant element to that of elemental Al, the more exothermic is the dissociative adsorption of O2 and the stronger are the bonds between the resulting O atoms and the surface. Additionally we show that the Mulliken concept of electronegativity can be applied in the prediction of the dissociative adsorption energy of O2 on the doped surfaces. The Mulliken modified second-stage electronegativity of the dopant atom is proportional to the exothermicity of the dissociative adsorption of O2. For the same dopant element in an adatom position the dissociation of O2 is more exothermic when compared to the case where the dopant occupies a substitutional position. These observations are discussed in view of the overlap population densities of states (OPDOS) computed as the overlap between the electronic states of the adsorbate O atoms and the clusters. It is shown that a more covalent character in the bonding between the Al surface and the dopant atom causes a more exothermic dissociation of O2 and stronger bonding with the O atoms when compared to a more ionic character in the bonding between the dopant and the Al surface. The extent of the adsorption site reconstruction is dopant atom dependent and is an important parameter for determining the mode of adsorption, adsorption energy and electronic structure of the product of O2 adsorption. The PBE0 functional could predict the existence of the O2 molecular adsorption product for many of the cases investigated here.

Enhanced hydrogen formation during the catalytic decomposition of H2O2 on metal oxide surfaces in the presence of HO radical scavengers.

Presently and for the foreseeable future, hydrogen peroxide and transition metal oxides are important constituents of energy production processes. In this work, the effect of the presence of HO radical scavengers on the product yield from the decomposition of H2O2 on metal oxide surfaces in aqueous solution was examined experimentally. Scavenging the intermediate product HO˙ by means of Tris or TAPS buffer leads to enhanced formation of H2. In parallel, a decrease in the production of the main gaseous product O2 is observed. Under these conditions, H2 formation is a spontaneous process even at room temperature. The yields of both the H2 and O2 depend on the concentration of Tris or TAPS in the reaction media. We observed that TAPS has a higher affinity for the surface of ZrO2 than does Tris. The difference in adsorption of both scavengers is reflected by the difference in their influence on the product yields. The observed sensitivity of the system H2O2-ZrO2 towards the two different scavengers indicates that O2 and H2 are formed at different types of surface sites.

Reactivity of metal oxide clusters with hydrogen peroxide and water--a DFT study evaluating the performance of different exchange-correlation functionals.

We have performed a density functional theory (DFT) investigation of the interactions of H2O2, H2O and HO radicals with clusters of ZrO2, TiO2 and Y2O3. Different modes of H2O adsorption onto the clusters were studied. In almost all the cases the dissociative adsorption is more exothermic than molecular adsorption. At the surfaces where H2O has undergone dissociative adsorption, the adsorption of H2O2 and the transition state for its decomposition are mediated by hydrogen bonding with the surface HO groups. Using the functionals B3LYP, B3LYP-D and M06 with clusters of 26 and 8 units of ZrO2, the M06 functional performed better than B3LYP in describing the reaction of decomposition of H2O2 and the adsorption of H2O. Additionally, we investigated clusters of the type (ZrO2)2, (TiO2)2 and (Y2O3) and the performance of the functionals B3LYP, B3LYP-D, B3LYP*, M06, M06-L, PBE0, PBE and PWPW91 in describing H2O2, H2O and HO˙ adsorption and the energy barrier for decomposition of H2O2. The trends obtained for HO˙ adsorption onto the clusters are discussed in terms of the ionization energy of the metal cation present in the oxide. In order to correctly account for the existence of an energy barrier for the decomposition of H2O2, the functional used must include Hartree-Fock exchange. Using minimal cluster models, the best performance in describing the energy barrier for H2O2 decomposition was obtained with the M06 and PBE0 functionals - the average absolute deviations from experiments are 6 kJ mol(-1) and 5 kJ mol(-1) respectively. With the M06 functional and a larger monoclinic (ZrO2)8 cluster model, the performance is in excellent agreement with experimental data. For the different oxides, PBE0 was found to be the most effective functional in terms of performance and computational time cost.

Experimental and molecular dynamics simulation study of the sublimation and vaporization energetics of iron metalocenes. crystal structures of Fe(eta5-C5H4CH3)2 and Fe[(eta5-(C5H5)(eta5-C5H4CHO)].

The standard molar enthalpies of sublimation of ferrocene, 1,1'-dimethylferrocene, decamethylferrocene, ferrocenecarboxaldehyde and alpha-methylferrocenemethanol, and the enthalpy of vaporization of N,N-dimethyl(aminomethyl)ferrocene, at 298.15 K, were determined by Calvet-drop microcalorimetry and/or the Knudsen effusion method. The obtained values were used to assess and refine our previously developed force field for metallocenes. The modified force field was able to reproduce the deltasubHdegreesm and deltavapHdegreesm values of the test-set with an accuracy better than 5 kJ.mol-1, except for decamethylferrocene, in which case the deviation between the calculated and experimental deltasubHdegreesm values was 16.1 kJ.mol-1. The origin of the larger error found in the prediction of the sublimation energetics of decamethylferrocene, and which was also observed in the estimation of structural properties (e.g., density and unit cell dimensions), is discussed. Finally, the crystal structures of Fe(eta5-C5H4CH3)2 and Fe[(eta5-(C5H5)(eta5-C5H4CHO)] at 293 and 150 K, respectively, are reported.