Adsorption of Carbon Dioxide on Mono-Layer Thick Oxidized Samarium Films on Ni(100)

Studies of adsorption of CO2 on nanoscopic surfaces are relevant for technological applications in heterogeneous catalysis as well as for sorption of this important greenhouse gas. Presently, adsorption of carbon dioxide on pure and oxidized thin samarium layers near mono-layer thickness on Ni(100) has been investigated by photoelectron spectroscopy and temperature programmed desorption. It is observed that very little CO2 adsorb on the metallic sample for exposures in the vacuum regime at room temperature. For the oxidized sample, a large enhancement in CO2 adsorption is observed in the desorption measurements. Indications of carbonate formation on the surface were found by C 1s and O 1s XPS. After annealing of the oxidized samples to 900 K very little CO2 was found to adsorb. Differences in desorption spectra before and after annealing of the oxidized samples are correlated with changes in XPS intensities, and with changes in sample work function which determines the energy difference between molecular orbitals and substrate Fermi level, and thus the probability of charge transfer between adsorbed molecule and substrate.

First-Principles Study of Nitrogen Adsorption and Dissociation on PuH2 (111) Surface

Plutonium mononitride is one of the main fuels for Generation IV reactors and can be prepared from nitrogenation of plutonium hydride. We investigated the adsorption and dissociation of nitrogen on PuH2 (111) surface to elaborate the initial stage of nitrogenation. The adsorption energies varied greatly with respect to the adsorption sites and orientations of the adsorbed molecule. The nitrogen exhibited preferential adsorption above the ccp site, where the molecular nitrogen was nearly parallel to the PuH2 surface and pointed to the nearest Pu atom. The orbital hybridization and the electrostatic attraction between the Pu and N weakened the N-N bond in the adsorbed molecule. The mechanism of the dissociation process was investigated within transition state theory, and the analysis of the activation barrier indicated that dissociation of nitrogen is not the rate-determining step of nitrogenation. These findings can contribute to a better understanding of the nuclear fuel cycle.

Small Crown-Ether Complexes as Molecular Models for Dihydrogen Adsorption in Undercoordinated Extraframework Cations in Zeolites

1:1 metal complexes of small crown-ethers are structurally similar to extraframework sites in metal-exchanged zeolites. Using <i>ab initio</i> calculations, we show that adsorbed molecular hydrogen follows the same trends in adsorption energies and vibrational frequencies at both types of metal sites. Unlike zeolites, crown-ethers can be characterized in the gas phase, which opens new possibilities for understanding the bonding of dihydrogen at undercoordinated metal sites to help guide the rational design of porous materials for hydrogen isotope separation. Because more strongly binding adsorbates affect the geometry of the hosts, the similarity of crown-ethers and zeolites with regard to the vibrational spectra of the adsorbed molecule seems to be limited to H₂.

Small Crown-Ether Complexes as Molecular Models for Dihydrogen Adsorption in Undercoordinated Extraframework Cations in Zeolites

1:1 metal complexes of small crown-ethers are structurally similar to extraframework sites in metal-exchanged zeolites. Using <i>ab initio</i> calculations, we show that adsorbed molecular hydrogen follows the same trends in adsorption energies and vibrational frequencies at both types of metal sites. Unlike zeolites, crown-ethers can be characterized in the gas phase, which opens new possibilities for understanding the bonding of dihydrogen at undercoordinated metal sites to help guide the rational design of porous materials for hydrogen isotope separation. Because more strongly binding adsorbates affect the geometry of the hosts, the similarity of crown-ethers and zeolites with regard to the vibrational spectra of the adsorbed molecule seems to be limited to H₂.

Calculating the absolute adsorption of high-pressure methane on shale by a new method

Currently, many adsorption experiments of methane on shale have been done to understand adsorption characteristics of methane on shale, but those experiments’ pressure and temperature are far less than reservoir pressure and temperature; therefore, we carried out the experiments of methane adsorption on shale at 75.6°C and 95.6°C with 0–50 MPa pressure range to study the adsorption characteristics of shale under reservoir condition. We also build a new method to calculate the real (absolute) adsorption of methane on shale. Results present that the characteristics of excess adsorption isotherm under high pressure is different from the characteristics of excess isotherm under low pressure; adsorption obtained by adsorption experiment increases with pressure going up until reaching a peak and then declines with further increase in pressure. We build a new method to calculate the absolute adsorption by assuming that the adsorption phase volume approximately equals to the total volume occupied by adsorbed molecule, and the results calculated by our method show this method is reasonable and effective.

Adsorption behavior of CO2 molecule on AlN and silicene—application to gas capture devices

Carbon dioxide contributes significantly to both global warming and climate change, processes that inflict major environmental damage, which is why it is of much interest to find a material that can adsorb carbon dioxide before it enters the atmosphere. In our study, we use first-principles calculations based on the density functional theory to investigate the adsorption of carbon dioxide on two-dimensional materials due to their unique chemical and physical properties. The two-dimensional materials we used include aluminum nitride, defected aluminum nitride, and silicene. We observed a negative adsorption energy of carbon dioxide on all three materials, signifying a spontaneous adsorption. Our charge analysis reveals a charge transfer from the materials to the molecule in addition to a significant overlap between the projected density of states spectra of the interacting atoms, all indicating the formation of chemical bonds between the material and adsorbed molecule. Our findings thus suggest that all the materials we used could be an effective adsorbent for carbon dioxide; however, the defected aluminum nitride sheet formed stronger bonds with carbon dioxide compared to the pure sheet. The application of our research could help decrease the world’s carbon footprint by creating devices to capture carbon dioxide before it enters the atmosphere.

Thermal desorption induced by chemical reaction on dust surface

ABSTRACT We propose a new mechanism of desorption of molecules from dust surface heated by exothermic reactions and derive a formula for the desorption probability. This theory includes no parameter that is physically ambiguous. It can predict the desorption probabilities not only for one-product reactions but also for multiproduct reactions. Furthermore, it can predict desorption probability of a pre-adsorbed molecule induced by a reaction at a nearby site. This characteristic will be helpful to verify the theory by the experiments which involve complex reaction networks. We develop a quantitative method of comparing the predicted desorption probability with the experiments. This method is also applied to the theories proposed so far. It is shown that each of them reproduces the experiments with similar precision, although the amount of systematic experimental data that give definite desorption probability are limited at present. We point out the importance of clarifying the nature of the substrate used in the experiment, in particular, its thermal diffusivity. We show a way to estimate the substrate properties from systematic desorption experiments without their direct measurements.

INVESTIGATION OF ADSORPTION ABILITY OF DIAMINOMALEODINITRILE ON NICKEL SURFACE BY ELLIPSOMETRIC METHOD

The difficulty of the discharge of nickel ions due to the adsorption of the addition of diaminomeleodinitrile on the electrode surface contributes to the formation of a fine crystalline precipitate with high reflectivity. Therefore, in this work, we studied the adsorption capacity of diaminomeleodinitrile on the surface of nickel from borate buffer solution in the cathodic and anodic regions. The values of its free adsorption energy were determined, which were at a potential of -0.65 V - 39.7 kJ / mol, and at 0.2 V - 66.2 kJ / mol. It was determined that diaminomeleodinitrile has adsorbed on the surface of nickel from borate buffer solution at pH = 7.4 mainly due to the forces of chemical interaction. It has been established that on the oxidized nickel surface, the adsorption of diaminomeleodinitrile begins in the region of lower concentrations compared to the “clean” surface. On average, a monolayer has formed within 60-75 min, while changes in the phase angle of the reflected light are small, due to the small size of the adsorbed molecule. It was determined that on the oxidized surface these changes are more than on the “clean” one. By method of reflective ellipsometry, which allows to measure and analyze the differences in the polarization parameters of a plane polarized light flux incident at an angle on two homogeneous media with different optical properties, the thickness of the resulting monolayer was determined. On an oxidized surface, it was ~ 0.5 nm, and on a “clean” surface, ~ 0.2 nm. When comparing these thicknesses with the size of the diaminomeleodinitrile molecule, it can be assumed that at a potential of 0.2 V, the diaminomeleodinitrile molecules are drawn out at an angle to the nickel surface, and at a potential of -0.65 V they are adsorbed flat on the nickel surface.

Structure and Electronic Properties of TiO2 Nanoclusters and Dye–Nanocluster Systems Appropriate to Model Hybrid Photovoltaic or Photocatalytic Applications

We report the results of a computational study of TiO2 nanoclusters of various sizes as well as of complex systems with various molecules adsorbed onto the clusters to set the ground for the modeling of charge transfer processes in hybrid organic–inorganic photovoltaics or photocatalytic degradation of pollutants. Despite the large number of existing computational studies of TiO2 clusters and in spite of the higher computing power of the typical available hardware, allowing for calculations of larger systems, there are still studies that use cluster sizes that are too small and not appropriate to address particular problems or certain complex systems relevant in photovoltaic or photocatalytic applications. By means of density functional theory (DFT) calculations, we attempt to find acceptable minimal sizes of the TinO2n+2H4 (n = 14, 24, 34, 44, 54) nanoclusters in correlation with the size of the adsorbed molecule and the rigidity of the backbone of the molecule to model systems and interface processes that occur in hybrid photovoltaics and photocatalysis. We illustrate various adsorption cases with a small rigid molecule based on coumarin, a larger rigid oligomethine cyanine dye with indol groups, and the penicillin V antibiotic having a flexible backbone. We find that the use of the n = 14 cluster to describe adsorption leads to significant distortions of both the cluster and the molecule and to unusual tridentate binding configurations not seen for larger clusters. Moreover, the significantly weaker bonding as well as the differences in the density of states and in the optical spectra suggest that the n = 14 cluster is a poor choice for simulating the materials used in the practical applications envisaged here. As the n = 24 cluster has provided mixed results, we argue that cluster sizes larger than or equal to n = 34 are necessary to provide the reliability required by photovoltaic and photocatalytic applications. Furthermore, the tendency to saturate the key quantities of interest when moving from n = 44 to n = 54 suggests that the largest cluster may bring little improvement at a significantly higher computational cost.

Can Adsorption on Graphene be Used for Isotopic Enrichment? A DFT Perspective

We have explored the theoretical applicability of adsorption on graphene for the isotopic enrichment of aromatic compounds. Our results indicate that for nonpolar molecules, like benzene, the model compound used in these studies shows a reasonable isotopic fractionation that is obtained only for the deuterated species. For heavier elements, isotopic enrichment might be possible with more polar compounds, e.g., nitro- or chloro-substituted aromatics. For benzene, it is also not possible to use isotopic fractionation to differentiate between different orientations of the adsorbed molecule over the graphene surface. Our results also allowed for the identification of theory levels and computational procedures that can be used for the reliable prediction of the isotope effects on adsorption on graphene. In particular, the use of partial Hessian is an attractive approach that yields acceptable values at an enormous increase of speed.