Preferred Adsorption Sites Research Articles

Sulfur dioxide interaction with thin iron oxide films on low-index surfaces of iron

The adsorption of sulfur dioxide (SO2) at room temperature on iron oxide surfaces has been studied using core-level photoelectron spectroscopy. A variety of iron oxides, from adsorbate structure to thin film, with different stoichiometries and terminations were grown on common low-index single crystal iron surfaces to model a range of structures in the initial stages of atmospheric oxidation. This permits well-controlled comparisons of differences and similarities in SO2 interaction.Both non-dissociative and dissociative adsorption of SO2 were observed, to different relative and absolute coverages, on all surfaces. The only identified non-dissociated species is SO4. For all surfaces, at least some amounts of atomic sulfur are observed while only for the submonolayer adsorbate structure, also tentative dimerization of sulfur into S2 or formation of S-Osurface is observed. For the two oxides terminated by a complete well-ordered oxygen layer, the absolute sulfur coverage is low. The complete oxygen layer terminated oxide film exhibiting a moiré-pattern had a saturation coverage of one SO4 species per surface super cell, which indicates a tentative preferred adsorption site. The surface showing the highest SO4 formation is the Fe3O4(100) thin film surface with a corrugated row structure. The SO4 formation is suggested between surface oxygen atoms within the same row.

Interaction of propionate and ethylamine on kagome phosphorene nanoribbons – A DFT study

• The geometric stability of kagome phosphorene nanoribbon (KPh-NR) is ensured. • The KPh-NR is used as base substrate to adsorb alanine, ethylamine and propionate molecules. • Alanine, ethylamine and propionate malodorous molecules are physisorbed on KPh-NR. • The findings recommend that KPh-NR can be used to probe alanine, ethylamine and propionate malodorous molecules. In the proposed work, the novel kagome phosphorene nanoribbon (KPh-NR) is built and studied the adsorption behaviour of alanine, ethylamine, and propionate malodorous molecules on KPh-NR surface using the ab-initio method. The chief KPh-NR shows semiconductor type with a band gap of 1.133 eV. Originally, the dynamical and structural stability was substantiated with the support of real frequency in the phonon band structure and exhibits negative cohesive energy (−4.02 eV per atom) correspondingly. The electronic characteristics of KPh-NR are studied using significant factors, namely the density of state maps and band structure. Moreover, two different preferential adsorption sites (hollow and triangle site) of target malodorous on KPh-NR were explored by the support of prominent parameters, namely binding energy & Bader charge transfer. The energy of binding for prominent adsorption sites are perceived in the scope of −0.115 to −0.616 eV. It is evident that the target malodorous physisorbed on KPh-NR. The findings suggested that KPh-NR can be successfully employed as a chemical nanosensor to detect the analine, ethylamine, and propionate molecules in the environment.

Photocatalytic production of H2O2 from water and dioxygen only under visible light using organic polymers: Systematic study of the effects of heteroatoms

The photocatalytic production of H2O2 that needs dioxygen, water, and light only has been proposed and investigated. However, most of the studies employed organic electron donors. In this work, organic photocatalysts that can produce H2O2 without organic electron donors are designed with a bottom-up approach. Although the heptazine-based g-C3N4 cannot induce water oxidation, a different kind of organic polymer (CN) obtained from the condensation of s-triazine and pyrimidine can produce H2O2 via dioxygen reduction coupled with water oxidation. The incorporation of O and P elements in CN structure (CNO, CNP, CNOP) increases the visible light absorption and hinders the photodecomposition of H2O2, respectively. The C-O and P-O bonds act as the charge trapping sites and also the preferred adsorption sites of a key intermediate, •OOH. As a result, the CNOP exhibits the highest production of H2O2 using dioxygen, water, and visible light only.

DFT Study of adsorption and diffusion of [formula omitted] and related species on [formula omitted] surfaces

An extensive study of adsorption and diffusion of O,O2,OH and H2O on Cu(100) surfaces was performed by means of DFT calculations. The adsorption distances and energies of the different species on top, hollow and bridge sites of the Cu(100) surface were calculated in order to elucidate preferential adsorption sites. All these calculations were done in conjunction with a study of charge distribution. The O,O2 and OH species, were found to adsorb preferentially on hollow, while H2O was found to adsorb on top, through the oxygen atom. Also, diffusion of each species from the most stable adsorption site to the nearest neighbouring site was studied in order to obtain diffusion barriers and diffusion velocity values. The diffusion of H2O and OH was found to be faster than the other species, whereas the O2 molecule was the lowest.

Removal of hydrogen sulfide from a binary mixture with methane gas, using IRMOF-1: a theoretical investigation.

The natural gas is mainly composed by methane, ethane, propane, and contaminants. Among these contaminants, the H2S gas has some specific characteristics such as its toxicity and corrosion, besides reducing the combustion power efficiency of natural gas. In this context, metal-organic frameworks appear as promising materials for purification of natural gas by adsorption, due to their large surface area and pore volume. In this work, Grand Canonical Monte Carlo method was used to study the adsorption and separation of CH4:H2S mixture by IRMOF-1. The adsorption isotherms were computed for the pure components, and at different compositions of binary mixture (90:10, 75:25, 50:50, 25:75, and 10:90). Interaction energy obtained with the semiempirical method confirmed that the inorganic unit is the preferred site for CH4 and H2S adsorption. Moreover, in a gas mixture with 50:50 proportion of CH4:H2S mixture, methane adsorbs preferentially in the inorganic unit only at pressures close to 20bar. Non-covalent interaction (NCI) analyses indicated that the interactions involving H2S are more effective than that for CH4, due to an electrostatic character in the H2S interaction. The simulations also showed that the separation of gases occurs in all compositions and pressures studied, suggesting that IRMOF-1 has a promising potential for this application.

Sorption studies of sulfadimethoxine and tetracycline molecules on β-antimonene nanotube - A first-principles insight

We ascertained the structural firmness of β-antimonene nanotube and studied the adsorption behaviour of sulfadimethoxine (SM) and tetracycline (TC) molecules on the base substrate using density functional theory (DFT) with B86LYP-D3 level of theory. Significantly, β-antimonene nanotube displays a semiconducting character with an energy band-gap of 0.263 eV. The three dissimilar preferential adsorption sites namely, bride-, hollow-, tube-inner site of SM and TC molecules on β-antimonene nanotube were investigated using average band gap changes, Bader charge transfer along with adsorption energy. Further, the calculated adsorption energy for preferential adsorption sites is noticed to be in the scope of −0.813 eV to −3.752 eV signifying to physisorption and chemisorption form of interaction on β-antimonene nanotube. The inclusive outcome recommends that β-antimonene nanotube can be deployed as a chemi-resistive sensor to sense and remove SM and TC molecules from the contaminated aqueous medium.

Pore size analysis of carbons with heterogeneous kernels from reactive molecular dynamics model and quenched solid density functional theory

We presented a new kernel of heterogenous carbon surfaces constructed using the reactive molecular dynamics model (rMD). The rMD model explicitly incorporates edges and corrugations resulting from the oxidative etching of graphene walls. The rMD model eliminates the computational artifacts characteristic to the homogeneous pore wall models. In ultramicropores, early uptake is guided by the competition between central energetic adsorption sites and heterogeneities of the wall. In the larger pores, the central energy diminishes and the preferential adsorption sites are located in the pore wall. Comparisons between the rMD model, which mimics the surface roughness explicitly, and the quenched solid density functional theory (QSDFT) model are performed. The rMD model performs similarly to the QSDFT in the reproduction of the carbon experimental isotherms, indicating that it is a viable alternative to the implicit models for carbon characterization. In calculated PSDs, the rMD model attributes higher volumes to the ultramicropores than the QSDFT model due to enhanced adsorption on the surface defects. Finally, we tested the influence of the N2 molecular probe models on adsorption isotherms. It is found that the discrepancies between the nitrogen probe models on heterogeneous wall surfaces are smaller than those for the homogeneous models.

A comprehensive investigation of the intermolecular interactions between CH2N2and X12Y12(X = B, Al, Ga; Y = N, P, As) nanocages

In this paper, we have theoretically determined the possibility of adsorption of the gaseous CH2N2molecule on the surface of X12Y12nanocages, where X = B, Al, Ga and Y = N, P, As. The electronic structure calculations have been performed by density functional theory (DFT) using four functionals (i.e., B3LYP-D3, M06-2X, ωB97XD, and CAM-B3LYP), together with the 6-311G(d) basis function. We find that the adsorption of CH2N2on top of the X–Y bond of the nanocage is the most preferred site for adsorption. The adsorption process is accompanied by a charge-transfer phenomenon, which results in a strong bond between the terminal N atom of diazomethane and the X atom of the nanocage. This gives rise to significant changes in the highest and lowest occupied molecular orbital (HOMO and LUMO, respectively) energies and thus attribute properties to the nanocages that enable them to act as building blocks of CH2N2sensing materials.

Efficient hydrogenation catalyst designing via preferential adsorption sites construction towards active copper

Based on the experimental and DFT calculation results, here for the first time we built preferential adsorption sites for nitroarenes by modification of the supported Cu catalysts surface with 1,10-phenathroline (1,10-phen), by which the yield of aniline via reduction of nitroarene is enhanced three times. Moreover, a macromolecular layer was in-situ generated on supported Cu catalysts to form a stable macromolecule modified supported Cu catalyst, i.e., CuAlOx-M. By applying the CuAlOx-M, a wide variety of nitroarene substrates react smoothly to afford the desired products in up to > 99% yield with > 99% selectivity. The method tolerates a variety of functional groups, including halides, ketone, amide, and C = C bond moieties. The excellent catalytic performance of the CuAlOx-M can be attributed to that the 1,10-phen modification benefits the preferential adsorption of nitrobenzene and slightly weakens adsorption of aniline on the supported nano-Cu surface.

Adsorption behaviour of trichloropropane and tetrachloroethylene on δ-phosphorene sheets: A first-principles insight

We determined the structural firmness of delta phosphorene nanosheet (del-PNS) and investigated the adsorption behaviour of hazardous halogenated compounds such as trichloropropane (TCP) and tetrachloroethylene (TCE) on del-PNS based on the framework of density functional theory. The stability of del-PNS is ensured with a formation energy of −3.81 eV/atom. Also, the energy gap of isolated del-PNS is observed as 0.22 eV indicating semiconductor behaviour. Particularly, three different preferential adsorption sites including bridge, hollow and top site of TCP and TCE molecules on del-PNS were studied with the influence of adsorption energy, Bader charge transfer, and average band gap changes. Further, the calculated adsorption energy of preferential adsorption sites is noticed to be in the range of −0.09 eV to −0.60 eV supporting the physisorption type of adsorption of chief halogenated compounds on del-PNS. The variation of electronic properties such as band gap variation, electron difference density, and charge transfer are noticed owing to adsorption of TCP and TCE on del-PNS. The overall outcomes suggest that the del-PNS can be practically used to detect TCP and TCE halogenated compounds.

Molecular Dynamics Simulation of Ion Adsorption and Ligand Exchange on an Orthoclase Surface.

Orthoclase (K-feldspar) is one of the natural inorganic materials, which shows remarkable potential toward removing heavy metal ions from aqueous solutions. Understanding the interactions of the orthoclase and metal ions is important in the treatment of saline wastewater. In this paper, molecular dynamics simulations were used to prove the adsorption of different ions onto orthoclase. The adsorption isotherms show that orthoclase has remarkable efficiency in the removal of cations at low ion concentrations. Aluminol groups are the preferential adsorption sites of cations due to higher negative charges. The adsorption types and adsorption sites are influenced by the valence, radius, and hydration stability of ions. Monovalent cations can be adsorbed in the cavities, whereas divalent cations cannot. The hydrated cation may form an outer-sphere complex or an inner-sphere complex in association with the loss of hydration water. Na+, K+, and Ca2+ ions mainly undergo inner-sphere adsorption and Mg2+ ions prefer outer-sphere adsorption. On the basis of simulation results, the mechanism of ion removal in the presence of orthoclase is demonstrated at a molecular level.

Partial Order–Disorder Transformation of Interpenetrated Porous Coordination Polymers

Controlling interpenetration and flexibility behaviors is intriguing and fundamental for porous coordination polymers. We report exceptional interpenetration behaviors involving controllable partia...

Stability Changes in Iridium Nanoclusters via Monoxide Adsorption: A DFT Study within the van der Waals Corrections.

Small iridium nanoclusters are prominent subnanometric systems for catalysis-related applications, mainly because of a large surface-to-volume ratio, noncoalescence feature, and tunable properties, which are completely influenced by the number of atoms, geometry, and molecular interaction with the chemical environment. Herein, we investigate the interaction between Irn nanoclusters (n = 2-7) and polluting molecules, CO, NO, and SO, using van der Waals D3 corrected density functional theory calculations. Starting from a representative structural set, we determine the growth pattern of the lowest energy unprotected Irn nanoclusters, which is based on open structural motifs, and from the adsorption of a XO (X = C, N, and S) molecule, the preferred high-symmetric adsorption sites were determined, dominated by the onefold top site. For protected systems, 4XO/Ir4 and 6XO/Ir6, we found a reduction in the total magnetic moment, while the equilibrium bonds of the nanoclusters expanded (contracted) due to mCO and mNO (mSO) adsorption, with exceptions for systems with large structural distortions (4SO/Ir4 and 6NO/Ir6). Meanwhile, the C-O and N-O (S-O) bond strength decreases (increases) following an increase (decrease) in the C-O and N-O (S-O) distances upon adsorption. We show, through energetic analysis, that for the different chemical environments, relative stability changes occur from the most stable unprotected nanoclusters, planar square (Ir4), and prism (Ir6) to higher energy isomers. The change in the stability order between the two competing protected systems is feasible if the balance between the interaction energy (additive term) and distortion energies (nonadditive terms) compensates for the relative total energies of the unprotected configurations. For all systems, the interaction energy is the main reason responsible for stability alterations, except for 4SO/Ir4, where the main contribution is from a small penalty due to Ir4 distortions upon adsorption, and for 4NO/Ir4, where the energetic effects from the adsorption do not overcome the difference between the binding energies of the unprotected nanoclusters. Finally, from energy decomposition and Hirshfeld charge analysis, we find a predominant covalent nature of the physical contributions in mOX···Irn interactions with a cationic core (Irn) and an anionic shell (XO coverage).

Stability and reaction thermodynamics of boron-doped nitrogenated holey graphene (NHG) monolayers and their energy storage properties for Li, Na and K-ion batteries: A first principles investigation

A comprehensive first principles investigation is performed to address the stability, reaction thermodynamics and the electrochemical properties C2N1−xBx and C2B monolayers for the use as the anodes in alkali metal ion batteries (Li, Na and K). The formation of C2N1−xBx structures in terms of the substituting of N in C2N monolayer by B atom is found to the thermodynamically spontaneous above the room temperature. The reaction thermodynamics in the combination with the first principles molecular dynamics simulations confirm the optimal experimental conditions for the preparation of C2N1−xBx or C2B should be a reaction directly between C2N and B element at the moderately high temperature in the range from 500 K to 900 K in the vacuum. For the electrochemical properties, the B-doped C2N show a systematic improvement on theoretical capacities, open circuit voltages and ion diffusion dynamics over those of C2N especially for B-rich C2N1−xBx structures. Nevertheless, owing to its small molar mass and less prominent adsorption site preferences, the overall electrochemical performances of C2B are much superior to those of C2N and ternary C2N1−xBx. Specifically, the theoretical capacities of C2B are predicted to be Li (1546 mAh/g), Na (663 mAh/g) and K (411 mAh/g), respectively. The migration energy barrier heights of C2N1−xBx and C2B are found to be much lower than those of C2N monolayer for the favorable diffusion pathways. Overall, the C2B monolayer is considered as a new 2-D structural platform to provide the high theoretical capacities and small migration energies as the anodes for the alkali metal ion batteries.

PdZn bimetallic nanoparticles for CO2 hydrogenation to methanol: Performance and mechanism

By means of density functional theory calculation, an exploration is conducted into the catalytic performance and reaction mechanism of CO2 hydrogenation to methanol on Pd32Zn6 (alloy), Pd32Zn6 (shell/core), and Pd38 nanoparticles. The potential preferred adsorption sites and adsorption energies of all the reaction species are determined. In particular, the electronic structure analysis of CO2 adsorption reveals the significant orbital hybridization occurring between the adsorbed CO2 molecule and Pd atoms, indicating that CO2 molecule is desirably activated and fully prepared for further hydrogenation. Furthermore, the reaction energies and activation barriers to the elementary reactions involved in the HCOO pathway are calculated precisely for the three nanoparticles. Compared with Pd38, the kinetically preferred pathway of methanol synthesis has shown changes after the introduction of Zn, and the activation barrier to the rate-determining step of the reaction route is also reduced on Pd32Zn6 (alloy) and Pd32Zn6 (shell/core) nanoparticles. It is suspected that the PdZn nanoparticle with an alloy structure exhibits higher activity of CO2 hydrogenation to methanol than that with a shell/core structure, which is attributed to the former having a lower activation barrier to the rate-determining step.

Ab initio Study of Hydrogen Adsorption on Metal-Decorated Borophene-Graphene Bilayer

We studied the hydrogen adsorption on the surface of a covalently bonded bilayer borophene-graphene heterostructure decorated with Pt, Ni, Ag, and Cu atoms. Due to its structure, the borophene-graphene bilayer combines borophene activity with the mechanical stability of graphene. Based on the density functional theory calculations, we determined the energies and preferred adsorption sites of these metal atoms on the heterostructure’s borophene surface. Since boron atoms in different positions can have different reactivities with respect to metal atoms, we considered seven possible adsorption positions. According to our calculations, all three metals adsorb in the top position above the boron atom and demonstrate catalytic activity. Among the metals considered, copper had the best characteristics. Copper-decorated heterostructure possesses a feasible near-zero overpotential for hydrogen evolution reaction. However, the borophene-graphene bilayer decorated with copper is unstable with respect to compression. Small deformations lead to irreversible structural changes in the system. Thus, compression cannot be used as an effective mechanism for additional potential reduction.

Theoretical Investigation Of Coverage Effects Of CO Adsorption On Cu(100) Surface

This work investigates the CO adsorption on the metallic Cu(100) surface using periodic DFT computations. CO adsorption was studied at varying coverages from 1/16 ML to 1/1 ML for a combination of adsorption positions (4-fold, bridge and top). The results showed that adsorption energies are coverage dependent, however, not enough to identify the adsorption site and coverage. However, C-O stretching frequencies are almost unique for studied coverage and adsorption positions. CO adsorption energy changes between -250 kJ/mol to +21 kJ/mol; similarly, the vibrations’ range in the 1702 cm-1 to 2110 cm-1 interval, within the studied coverage and adsorption positions. Nevertheless, under the saturation coverage (θCO ≈ 0.55ML) the preferable adsorption site is the on-top position identified with a C-O stretching frequency around ~2100 cm-1 and with ~117 kJ/mol adsorption energy.

Oxygen adsorption on (100) surfaces in Fe\u2013Cr alloys

The adsorption of oxygen on bcc Fe–Cr(100) surfaces with two different alloy concentrations is studied using ab initio density functional calculations. Atomic-scale analysis of oxygen–surface interactions is indispensable for obtaining a comprehensive understanding of macroscopic surface oxidation processes. Up to two chromium atoms are inserted into the first two surface layers. Atomic geometries, energies and electronic properties are investigated. A hollow site is found to be the preferred adsorption site over bridge and on-top sites. Chromium atoms in the surface and subsurface layers are found to significantly affect the adsorption properties of neighbouring iron atoms. Seventy-one different adsorption geometries are studied, and the corresponding adsorption energies are calculated. Estimates for the main diffusion barriers from the hollow adsorption site are given. Whether the change in the oxygen affinity of iron atoms can be related to the chromium-induced charge transfer between the surface atoms is discussed. The possibility to utilize the presented theoretical results in related experimental research and in developing semiclassical potentials for simulating the oxidation of Fe–Cr alloys is addressed.

Insights into the interfacial interaction mechanisms of p-arsanilic acid adsorption on ionic liquid modified porous cellulose

Organoarsenic compounds are considered as emerging pollutants since they may decompose into highly toxic arsenate in the environment. The adsorption of organoarsenic compounds by natural polymers has drawn research attention, but the adsorption mechanisms remain largely unexplored. In this study, the sorption interfacial interaction mechanisms of p-arsanilic acid on ionic liquid modified celluloses were investigated systematically by sorption models, spectroscopy analysis techniques, and density functional theory calculations. Adsorption experiments showed that the modified cellulose exhibited high adsorption capacity (216.9 mg/g) and fast adsorption rate (3.21 × 10−3 g mg−1·min−1) toward p-ASA. Adsorption model studies revealed that the adsorption process was multilayer adsorption and dominated by the adsorption onto active site. The effect of environmental factors on p-arsanilic acid removal and spectroscopy analysis manifested that p-arsanilic acid interacted with the adsorbent through hydrogen bonding and π-π interaction to form outer-sphere complexes. Density functional theory calculation and independent gradient model analysis were used to analyze the interfacial interaction mechanisms, results of which showed that hydrogen bonding played the dominant role in the adsorption process and the imidazole group was preferential adsorption site. This work provides a valuable reference for understanding the role of weak force in the adsorption process between organoarsenic and adsorbents.

Advances in Post-Combustion CO2 Capture by Physical Adsorption: From Materials Innovation to Separation Practice.

The atmospheric CO2 concentration continues a rapid increase to its current record high value of 416 ppm for the time being. It calls for advanced CO2 capture technologies. One of the attractive technologies is physical adsorption-based separation, which shows easy regeneration and high cycle stability, and thus reduced energy penalties and cost. The extensive research on this topic is evidenced by the growing body of scientific and technical literature. The progress spans from the innovation of novel porous adsorbents to practical separation practices. Major CO2 capture materials include the most widely used industrially relevant porous carbons, zeolites, activated alumina, mesoporous silica, and the newly emerging metal-organic frameworks (MOFs) and covalent-organic framework (COFs). The key intrinsic properties such as pore structure, surface chemistry, preferable adsorption sites, and other structural features that would affect CO2 capture capacity, selectivity, and recyclability are first discussed. The industrial relevant variables such as particle size of adsorbents, the mechanical strength, adsorption heat management, and other technological advances are equally important, even more crucial when scaling up from bench and pilot-scale to demonstration and commercial scale. Therefore, we aim to bring a full picture of the adsorption-based CO2 separation technologies, from adsorbent design, intrinsic property evaluation to performance assessment not only under ideal equilibrium conditions but also in realistic pressure swing adsorption processes.