Differential Energy Of Adsorption Research Articles

High-efficiency adsorption of HF and HCN gases by transition metal X (X=Pd, Mo, Ni) doped WS2 :a first-principles study

Abstract This article studies the adsorption effect of pristine WS2 and Pd, Mo, Ni-doped WS2 on HF and HCN gases based on density functional theory. The energy band structure, density of states (DOS), charge differential density (CDD), adsorption energy, charge transfer, and molecular orbitals of the materials are calculated. The results show that Pd, Mo, Ni-doped WS2 significantly improve the adsorption energy of HF and HCN gases. Moreover, the Mo_WS2/HF system exhibits a charge transfer of 0.48 e, significantly higher than other systems. Mo_WS2 and Ni_WS2 systems exhibit an increase in transferred charges compared to pristine WS2 as adsorbing HCN, which are easy to adsorb HCN. Using recovery time as an indicator, Mo_WS2 is the most suitable for adsorbing HF between 300 K and 400 K, while Ni_WS2 is the most suitable for adsorbing HCN. Analyzed the application of materials in adsorbing harmful gases HF and HCN.

Sparkling Synergy: Enhancing Hydrogen Evolution with a Mesoporous CoP/FeP Interface.

The reaction kinetics is predominantly determined by the surface and interface engineering of electrocatalysts. Herein, we demonstrate the growth of cobalt monophosphide and iron monophosphide (CoP/FeP) with an effective solid interface. The surface of CoP/FeP is mesoporous, which is obtained by phosphidizing mesoporous CoFe2O4. The CoP/FeP electrode exhibits substantially superior hydrogen evolution reaction (HER) performance compared to CoP and FeP. The overpotentials (η) required to generate 10 mA cm-2 are determined to be around 98 mVRHE (CoP/FeP), 220 mVRHE (FeP), and 265 mVRHE (CoP) in an acidic electrolyte. The exchange current density and Tafel slopes suggest that CoP/FeP has better redox properties and kinetic abilities compared to FeP and CoP. Furthermore, the CoP/FeP electrode exhibits reduced electrochemical impedance and superior surface charge transport characteristics in comparison to both the CoP and FeP electrodes. In addition to having a greater number of catalytically active sites, the turnover frequency of CoP/FeP is approximately 2 and 5 times higher than that of FeP and CoP, respectively. The CoP/FeP electrode maintains a consistent current density of around 25 mA cm-2 for a continuous period of 24 h during the HER, attesting to the excellent durability of the CoP/FeP electrode. In addition, a relationship between differential hydrogen adsorption energy (ΔEH), the corresponding Gibbs free energy change (ΔGH), and the hydrogen coverage on distinct surfaces, namely, CoP, FeP, and CoP/FeP, is established. The calculation findings show that the CoP/FeP surface, which is predominantly exposed with CoP, exhibits the highest catalytic potential for the HER. The estimation of the specific HER activity of the electrodes, normalized to the electrochemically active surface area, corroborates the calculation findings.

Theoretical insight into the rearrangement of sulfur atoms on the Ni- and Cu-doped MoS2 S-edge induced by hydrogen adsorption under HDS reaction conditions.

Density functional theory (DFT) calculations and an atomistic thermodynamic approach were used to study the geometric rearrangement of sulfur atoms on the Ni- and Cu-doped MoS2 S-edge upon hydrogen adsorption. Under HDS conditions, thermodynamically stable hydrogenated structures were identified as SH groups on the undoped S-edge with 100% sulfur coverage, on the Ni-doped S-edge with 50% sulfur coverage and on the Cu-doped S-edge with 25% sulfur coverage. It was found that the rearrangement of the S atoms is essential to reach the most stable state at the edge for the undoped and Ni-doped S-edge. Hydrogen adsorption on the Ni-doped S-edge leads to the greatest amount of S rearrangement (ΔERearrang = 0.93 eV/H2). Our results suggest that under the reaction conditions, the H2 dissociative adsorption process is strongly coupled to the rearrangement of the sulfur atoms. By examining the differential hydrogen adsorption energy on the most stable edge structures, we found a plausible explanation for the trend in the hydrogenation activity of the doped edges. Our results suggest that Ni enhances the hydrogenation activity of the S-edge by decreasing the S-H bond strength, while Cu poisons it by increasing the S-H bond strength.

A fine 3d transition metal regulation strategy toward high-entropy alloy mesoporous nanotubes as efficient electrocatalysts

High-entropy alloys (HEAs) are attracting considerable attention because of their interesting catalytic features, intrinsic thermodynamic stability and diversity of components. Nevertheless, the precise shaping low-dimensional architectures and fine-regulated catalytic performance are still challenging for HEAs. Herein, we propose a cost-effective general template-triggered method to prepare a class of quinary to septenary HEA mesoporous nanotubes (HEA mNTs). In particular, we explore the electron structure–activity relationship toward HEA mNTs with different 3d transition metal regulation by experiments and DFT calculations. As a proof of demonstration, Fe-regulated senary HEA mNTs (PtPdRuIrFeCu mNTs) with ∼1.5 nm wall experimentally unveil the excellent mass activity of 1.94 A/mgPt (1.22 A/mgnoble metals) @ 0.9 VRHE for ORR, which is 7.46- (5.30-) fold higher than commercial Pt/C in 0.1 M KOH. Density functional theory results further reveal that the differential oxygen adsorption energy (EO) of PtPdRuIrFeCu is closest to the theoretical optimal EO, corresponding to excellent ORR activity. Additionally, the linear relationship between the differential EO of HEA and the d band center of pure metals can provide a rapid screening method for HEA catalysts. HEA mNTs reported in this work are a class of prospective catalysts for the fuel cells and water splitting devices, and the would-be applications in sensors and energy storages look bright because of their charming characteristics.

Computational Screening of Ti3C2TX MXene by Controlling the Functionalized Catalyst for NH3 Gas Sensor

First‐principles calculations are used to research the adsorption behavior of ammonia on Ti3C2O2, Ti3C2F2, Ti3C2H2, Ti3C2S2, and Ti3C2Cl2. Herein, a total of four special adsorption sites α, β, γ, and δ are considered. The adsorption energy, charge transfer, and electronic properties of the gas‐adsorption system are calculated, and the better adsorption sites and adsorption functional groups of ammonia on Ti3C2T X with different functional groups are studied. The results show that the best adsorption positions of ammonia on Ti3C2O2, Ti3C2F2, Ti3C2H2, Ti3C2S2, and Ti3C2Cl2 are all α position. According to the analysis of differential charge density, adsorption energy, and charge transfer of ammonia molecules, the adsorption strength of ammonia molecules on Ti3C2 surfaces modified with different functional groups is Ti3C2H2 > Ti3C2O2 > Ti3C2F2 > Ti3C2S2 > Ti3C2Cl2. The ammonia molecule adsorbs on the surface of Ti3C2H2 exhibits the strongest adsorption energy (−0.787 eV), but the −H group is more likely to break and form other groups. Therefore, the Ti3C2 surface modified by −O group is more suitable for ammonia detection.

Development of a novel sensor based on Bi2O3 and carbonized UIO-66-NH2 nanocomposite for efficient detection of Pb(Ⅱ) ion in water environment

Development of an efficient monitoring technology for rapid detection of toxic Pb(Ⅱ) ion in water environments is extremely important. Here, a novel and highly sensitive sensor was prepared using one-step calcination technique, based on Bi2O3 nanoparticles and carbonized metal–organic framework (MOF) nanocomposite. Scanning electron microscopy, transmission electron microscopy, contact angle and X-ray photoelectron spectroscopy characterization methods were used to analyze the morphology and structure of the prepared materials. Based on the electrical double-layer capacitance theory and Raman spectroscopy, changes to the active sites of different modified materials were investigated. Besides, differential charge densities and adsorption energies of the different modified materials in Zr-O clusters were calculated using density functional theory (DFT). A Bi2O3 and carbonized UIO-66-NH2 (Bi2O3/C-UIO-66-NH2) -modified glassy carbon electrode was used to detect Pb(Ⅱ) by differential pulse anodic stripping voltammetry. Under optimal experimental parameters, the developed electrochemical sensor has a wide linear range (2–130 μg/L) and a low detection limit (0.05 μg/L). Meanwhile, the sensor has excellent stability, repeatability, and anti-interference properties and has been successfully applied to detect Pb(Ⅱ) in actual water samples. The results of this paper show that our developed sensor an efficient and rapid sensor technology for monitoring lead in water environment.

Statistical Mechanical Model of Gas Adsorption in a Metal-Organic Framework Harboring a Rotaxane Molecular Shuttle.

Metal-organic frameworks (MOFs) are modular and tunable nanoporous materials with applications in gas storage, separations, and sensing. Integrating flexible/dynamic, gas-responsive components into MOFs can give them unique or enhanced adsorption properties. Here, we explore the adsorption properties that could be imparted to a MOF by a rotaxane molecular shuttle (RMS) in its pores. In the unit cell of an RMS-MOF, a macrocyclic wheel is mechanically interlocked with a strut of the MOF scaffold. The wheel shuttles between stations on the strut that are also gas adsorption sites. At a level of abstraction similar to the seminal Langmuir adsorption model, we pose and analyze a simple statistical mechanical model of gas adsorption in an RMS-MOF that accounts for (i) wheel/gas competition for sites on the strut and (ii) gas-induced changes in the configurational entropy of the shuttling wheel. We determine how the amount of gas adsorbed, the position of the wheel, and the differential energy of adsorption depend on temperature, pressure, and the interactions of the gas and wheel with the stations on the strut. Our model reveals that, compared to a rigid, Langmuir material, the chemistry of the RMS-MOF can be tuned to render gas adsorption more or less temperature sensitive and to release more or less heat upon adsorption. The model also uncovers that, if gas-wheel competition for a station is fierce, temperature influences the position of the wheel differently depending on the amount of gas adsorbed.

Framework for Scalable Adsorbate–Adsorbate Interaction Models

We present a framework for physically motivated models of adsorbate–adsorbate interaction between small molecules on transition and coinage metals based on modifications to the substrate electronic structure due to adsorption. We use this framework to develop one model for transition and one for coinage metal surfaces. The models for transition metals are based on the d-band center position, and the models for coinage metals are based on partial charges. The models require no empirical parameters, only two first-principles calculations per adsorbate as input, and therefore scale linearly with the number of reaction intermediates. By theory to theory comparison with explicit density functional theory calculations over a wide range of adsorbates and surfaces, we show that the root-mean-squared error for differential adsorption energies is less than 0.2 eV for up to 1 ML coverage.

Chirally-modified metal surfaces: energetics of interaction with chiral molecules.

Imparting chirality to non-chiral metal surfaces by adsorption of chiral modifiers is a highly promising route to create effective heterogeneously catalyzed processes for the production of enantiopure pharmaceuticals. One of the major current challenges in heterogeneous chiral catalysis is the fundamental-level understanding of how such chirally-modified surfaces interact with chiral and prochiral molecules to induce their enantioselective transformations. Herein we report the first direct calorimetric measurement of the adsorption energy of chiral molecules onto well-defined chirally-modified surfaces. Two model modifiers 1-(1-naphthyl)ethylamine and 2-methylbutanoic acid were used to impart chirality to Pt(111) and their interaction with propylene oxide was investigated by means of single-crystal adsorption calorimetry. Differential adsorption energies and absolute surface uptakes were obtained for the R- and S-enantiomers of propylene oxide under clean ultrahigh vacuum conditions. Two types of adsorption behavior were observed for different chiral modifiers, pointing to different mechanisms of imparting chirality to metal surfaces. The results are analyzed and discussed in view of previously reported stereoselectivity of adsorption processes.

Adsorption of CO2 in FAU zeolites: Effect of zeolite composition

Many technological processes, mainly in the energy sector, require separation of carbon dioxide from gas mixtures. For that purpose medium and large pore zeolites can be used, provided that the differential CO2 adsorption energy allows thermodynamic separation under equilibrium conditions. Hence the convenience to have a precise knowledge (at the molecular level) about the factors that control CO2 interaction with zeolites, and faujasite-type zeolites in particular, are most relevant in this context on account of their relatively high adsorption capacity. We report on a detailed spectroscopic, calorimetric and theoretical study on the effect of composition on equilibrium CO2 adsorption in alkali-metal exchanged faujasite-type zeolites, which, by combining experimental results with calculations performed at the DFT/CC level on a periodic model of the zeolite yields fine details on the CO2 adsorption complexes and corresponding gas–solid interaction energy. The results obtained are discussed in the broader context of other literature reports; showing, in particular, how the DFT/CC computational approach gives interaction energy values that are in better agreement with experimental data than those obtained using some other computational methods, which show larger limitations to account properly for dispersion interactions. We found out that: (i) dispersion interactions account for about 50% of the overall adsorption enthalpy of CO2 molecules in FAU zeolites, (ii) a very low (experimentally non-detectable) population of sites III and III′ was found for FAU zeolite with Si/Al ratio 2.55:1 and all CO2 molecules are adsorbed on sites II and are tilted toward the zeolite wall due to the stabilizing effect of dispersion interactions between CO2 and zeolite, and (iii) minor heterogeneity of adsorption sites present in the FAU samples originating from differences in the number and geometry of Al atoms in the 6R of sites II.

Origin of site preference of CO and NO adsorption on Pd(1 1 1) at different coverages: A density functional theory study

First-principles calculations based on density functional theory have been performed to investigate the adsorption of CO and NO on Pd(111) surface. The average and differential adsorption energies of CO and NO at the high-symmetry adsorption sites on Pd(111) at different coverages, namely 0.11, 0.25, 0.50, and 0.75ML are calculated. The results show that at low coverages of 0.11 and 0.25ML, both CO and NO are preferentially adsorbed at the threefold hollow sites. At the medium coverage of 0.50ML, CO molecules occupy both hollow and bridge sites with almost degenerate adsorption energies, while NO molecules prefer the hollow sites to the bridge sites, which can be attributed to the more corrugated potential energy surface of NO on Pd(111) surface. At high coverage of 0.75ML, both CO and NO form the p(3×3)- 3CO structures with the adsorbates at the hollow and atop sites. The calculated stretching vibrational frequencies are in good agreement with the experimental values. The electronic structure analysis shows that the adsorption of CO and NO on Pd(111) surface follows a donation and back-donation mechanism, and the high-coordinated sites promote the donation and back-donation process. The energy decomposition scheme indicates that the site preference at higher coverage is a compromise between the adsorbate–substrate interaction and adsorbate–adsorbate interaction. The relationship between the adsorption energies and the surface coverage has been well established, and linear relations are identified for both CO and NO. We suggest that the coverage-dependent adsorption energies of CO and NO on Pd(111) are useful parameters for the kinetic studies on the relevant catalytic reaction systems.

Searching for active binary rutile oxide catalyst for water splitting from first principles

Water electrolysis is an important route to large-scale hydrogen production using renewable energy, in which the oxygen evolution reaction (OER: 2H(2)O → O(2) + 4H(+) + 4e(-)) causes the largest energy loss in traditional electrocatalysts involving Ru-Ir mixed oxides. Following our previous mechanistic studies on the OER on RuO(2)(110) (J. Am. Chem. Soc. 2010, 132, 18214), this work aims to provide further insight into the key parameters relevant to the activity of OER catalysts by investigating a group of rutile-type binary metal oxides, including RuNiO(2), RuCoO(2), RuRhO(2), RuIrO(2) and OsIrO(2). Two key aspects are focused on, namely the surface O coverage at the relevant potential conditions and the kinetics of H(2)O activation on the O-covered surfaces. The O coverage for all the oxides investigated here is found to be 1 ML at the concerned potential (1.23 V) with all the exposed metal cations being covered by terminal O atoms. The calculated free energy barrier for the H(2)O dissociation on the O covered surfaces varies significantly on different surfaces. The highest OER activity occurs at RuCoO(2) and RuNiO(2) oxides with a predicted activity about 500 times higher than pure RuO(2). On these oxides, the surface bridging O near the terminal O atom has a high activity for accepting the H during H(2)O splitting. It is concluded that while the differential adsorption energy of the terminal O atom influences the OER activity to the largest extent, the OER activity can still be tuned by modifying the electronic structure of surface bridging O.

Performance of Cluster Expansions of Coverage-Dependent Adsorption of Atomic Oxygen on Pt(111).

A density functional theory (DFT) database of 66 Pt(111)/O formation energies is presented. We fit this database of formation energies to a range of cluster expansions (CEs) of systematically increasing size and flexibility. We find that the performance of the CE depends upon the property or properties of interest. Pair-wise CEs with up to third nearest neighbor interactions poorly predict all metrics. CEs with five to eight pairwise interactions and one to two triplet interactions predicted formation energies and most ground states accurately but predicted average and differential adsorption energies with modest errors. A larger CE captures average and differential adsorption energies as well as formation energies and ground states. The choice of figures in the CEs is also examined. Pair-wise figures and the linear, 1-1-3, triplet are necessary to obtain CEs that qualitatively reproduce the examined properties; however, other figures are more interchangeable. The electronic and strain components of the adsorbate-adsorbate interactions is studied by comparing a CE of DFT formation energies in which atoms were not allowed to relax to the CEs of the relaxed surface. On an unrelaxed Pt surface, interactions are shorter-ranged interactions and more repulsive at first nearest neighbor separation.

Relation between adsorption and catalysis in the case of NiO and Co 3O 4

Reversed flow-inverse gas chromatography is a quick, precise and effective methodology to characterize physicochemical properties of adsorbents. This is extended to the experimental measurement of the adsorption energy distribution function as well as of the differential energy of adsorption due to lateral interactions of molecules adsorbed on two catalysts, namely Co 3O 4 and NiO. Thus, the nature and the strength of the adsorbate–adsorbent and adsorbate–adsorbate interactions are extracted in order to give detailed answers to the questions: (a) where are the molecules on the heterogeneous surface and (b) which is the nature of the surface chemical bonds? Thus, adsorption of 1-butene was found to take place immediately and irreversibly. It holds a deep relation between adsorption and catalysis of 1-butene over these catalysts. As a consequence, the adsorption of 1-butene in the presence of hydrogen leads to isobutane and/or n-butane, depending on the temperature. It can be seen from the adsorption/desorption kinetic constants that the adsorption of 1-butene on Co 3O 4 is one order higher than over NiO. This fact in connection with the bigger activation energy and the lower kinetic coefficients concerning hydrogenation reaction over NiO shows that Co 3O 4 is a better catalyst for this kind of catalysis.

The role of surface heterogeneity and lateral interactions in the adsorption of volatile organic compounds on rutile surface

Volatile organic compounds (VOCs) are pollutants of great interest because they are very harmful for both human health and the environment, even at very low concentrations. In this work we present and discuss the results of the experimental chromatographic study of the role of surface heterogeneity and lateral interactions in the adsorption of volatile organic compounds – ethanol, acetaldehyde and acetone – on the surface of rutile (TiO 2), a typical oxide widely used as a white pigment and a photocatalyst, as well. The ethanol, acetaldehyde and acetone were chosen because they contain the same heteroatom (O) and they have small carbon-chains. The novel method of Reversed Flow-Inverse Gas Chromatography is used, which has a powerful mathematical background and comprises a simple experimental arrangement for the determination of energetic physicochemical quantities directly from the experimental data, by means of a time-resolved analysis. In particular, several important physicochemical quantities are determined, as local adsorption energy, local adsorption isotherm, local monolayer capacity, non-adsorbed gaseous concentration of adsorbate, density probability function for the adsorption energy values, as well as the differential energy of adsorption due to lateral interactions among molecules adsorbed on the heterogeneous solid surface of TiO 2. By means of these quantities, appropriate answers are achieved to critical questions of: (a) What is the type of the adsorption isotherm of a system? (b) Where are the adsorbed molecules located on the heterogeneous surface? (c) What is the nature of the surface bonds? (d) What is the type of non-ideality of the system and (e) How does the adsorbate affect the adsorbent properties?

Facile synthesis of sulfo-functionalized mesoporous silica with strong acidity by temperature-controlled calcination

The facile synthesis of sulfo-functionalized mesoporous silica (MCM-41) by a one-step process of surfactant removal and thiol oxidation technique through a temperature-controlled calcination of a precursor is presented. Thiol containing mesoporous silica is synthesized as a precursor by hydrolysis and co-condensation of tetramethoxysilane (TMOS) and mercaptopropyl trimethoxysilane (MPTMS). The samples thus prepared are shown to preserve the ordered two-dimensional hexagonal structure and pore characteristics of MCM-41, while functionalizing the material with sulfo groups which was oxidized from thiol groups providing strong acidity. The acidity of the material is demonstrated by high ammonia uptakes and low differential adsorption energy of ammonia.

High resolution adsorption isotherms of N2 and Ar for nonporous silicas and MFI zeolites

The high resolution adsorption isotherms of N2 (77.4 K) and Ar (87.3 K) have been measured for two nonporous silicas with different silanol contents (3.3 and 0.35 OH/nm2) and for two MFI zeolite with different Al contents (Si/Al=12.5 and 500). Silanol groups and Al sites (acid sites) gives the significant effect on the N2 isotherms at submonolayer, but the Ar isotherms are independent of silanols and Al sites. The Ar isotherms, therefore, are preferable in calculation of microporosity of zeolites. The N2 and Ar isotherms for MFI zeolite (Si/Al=500) have been measured at temperatures of 77–94 K, from which the differential adsorption energies of N2 and Ar are calculated. The interaction of N2 with channel surface of MFI zeolite is greater than that of Ar in the range of αs=0.1–0.7. The hystereses are detected for the N2 isotherm in p/po=0.1–0.3 at 77.4 K and for the Ar isotherm in p/po=3×10−4–2×10−3 at 87.3 K. However, it is difficult to explain the hysteresis phenomenon using differential adsorption energy.

Simulating temperature programmed desorption directly from density functional calculations: How adsorbate configurations relate to desorption features

DFT calculations are used to explain states in TPD spectra by relating the differential adsorption energies for different configurations to the desorption features. A plot of the number of molecules versus these temperatures strongly resembles the TPD spectrum. The calculations were also used to obtain pairwise additive potentials. These potentials were used in a dynamic Monte Carlo model to simulate the TPD spectrum. The spectra obtained from both approaches are in good agreement, validating the approximation that lateral interactions can be added on a pairwise basis.

Adsorption of Nitrogen on Granular Activated Carbon: Experiment and Modeling

A carbon adsorbent was produced and used to volumetrically measure nitrogen adsorption isotherms from 93 to 298 K and up to 7 MPa. The isosteric heat of adsorption was determined to range between -9.5 and -16 kJ/mol. The excess adsorption isotherms were modeled using an approach based on a modified Dubinin-Astakhov adsorption model, adapted for excess adsorption, which provided an accurate fit for all supercritical isotherms. An expression for the differential energy of adsorption as a function of pressure was developed using the Dubinin-Astakhov isotherm. The energy of adsorption for the isotherms measured was found to range from -8 to -15 kJ/mol as a function of pressure.

Monte carlo simulation of the polymolecular adsorption on an inhomogeneous surface with allowance for lateral interactions

A model of the polymoleculer adsorption on an inhomogeneous surface is presented. A procedure for calculating isotherms based on statistical data on the surface distribution of the material is suggested. The calculated isotherms and the dependences of the differential adsorption energy on the degree of filling are compared with the available experimental data for a benzene-graphitized soot system.