Grand Canonical Ensemble Monte Carlo Research Articles

Uncovering optimal carbon and boron nitride nanotube geometries for methane and hydrogen release

We screened 1651 carbon and boron nitride (BN) nanotubes to investigate methane release at 298 K and hydrogen release at 77 K through grand canonical ensemble Monte Carlo (GCMC) simulations. The effects of nanotube radius, density, and van der Waals spacing on the release quantities of these gases were explored. Our research shows that CH4 release in C(40,40) and BN(40,40) nanotubes reaches a high of 0.15 g/g, below the DOE's 0.5 g/g target. Similarly, the best nanotubes for volumetric release, C(21,9) and BN(18,18), peak at 175 cm³/cm³, below the DOE target of 330 cm³/cm³. This suggests that internal adsorption within isolated nanotubes is insufficient to meet DOE targets, highlighting the need for optimization of inter-tube van der Waals spacing. For H2, C(40,39) and BN(40,40) nanotubes are optimal for weight release, achieving up to 12.19% at a pressure of 8 MPa. This surpasses the 2025 DOE benchmark of 5.5 wt%. Meanwhile, C(28,7) and BN(24,24) nanotubes are most suitable for volumetric release. The C(28,7) nanotube, recommended for H2 storage, reaches a volumetric release quantity close to the DOE target of 0.04 kg/L at a van der Waals spacing of 1 nm. At pressures exceeding 2 MPa, the weight adsorption outside nanotubes accounts for 40–55% of the total, underscoring the pivotal role of extra-tube adsorption in gas storage capacity for both CH4 and H2. The results provide a foundation for the design of nanotube-based materials for efficient gas storage and release, with implications for clean energy applications.

Study on the Effect of H2S on the Adsorption of CH4, N2, and CO2 by Anthracite.

In order to study the effect of H2S on gas adsorption in a coal seam, the adsorption characteristics of single-component CO2, CH4, N2, and H2S and multicomponent H2S mixed with CO2, CH4, and N2 by anthracite were simulated by using the Grand Canonical Ensemble Monte Carlo (GCMC) method. The results show that the adsorption capacity of CO2, CH4, N2, and H2S in anthracite decreases with increasing temperature and increases with increasing pressure. The isothermal adsorption curves of CO2, CH4, N2, and H2S and different proportions of H2S/CH4, H2S/N2, and H2S/CO2 are highly consistent with the Langmuir equation, and the R 2 is above 0.99. Under different temperature and pressure conditions, the adsorption capacity of H2S and CO2 is stronger than that of coal for N2 and CH4, and the adsorption capacity difference is about 3 mmol/g. There is competitive adsorption among H2S, CO2, CH4, and N2, and H2S has a superior adsorption property. When H2S and other gases exist at the same time, the adsorption capacities of CH4, N2, and CO2 are reduced by 48-60%, 81-91%, and 51-66%, respectively.

Molecular simulation of adsorption and separation of N2 and CF4 on carbon and boron nitride nanostructures

Grand canonical ensemble Monte Carlo (GCMC) molecular simulations were performed to study CF4 adsorption on carbon nanotubes, boron nitride (BN) nanotubes, carbon nanoscrolls, and BN nanoscrolls. At 298 K and 2 MPa, (15,15) BN nanotubes exhibited 4.57 mmol/g and 98 v/v in excess weight and volume adsorption for CF4, respectively, which is a 50 % and 44 % increase over (15,15) carbon nanotubes at 3.04 mmol/g and 68 v/v. BN nanoscrolls with a 1.3 nm interlayer spacing showed even higher adsorption at 13.63 mmol/g and 145 v/v, a 33 % increase over carbon nanoscrolls with a 10.23 mmol/g and 108 v/v. Utilizing Ideal Adsorbed Solution Theory (IAST), we predicted that (14,14) BN nanotubes would have a CF4 adsorption capacity of 4.27 mmol/g and a selectivity of 6.4 at 298 K and 4 MPa for equimolar CF4/N2 mixtures, surpassing (14,14) carbon nanotubes at 3.01 mmol/g and 4.5. BN nanoscrolls with a 1.2 nm spacing showed a 13.35 mmol/g and 8.1 adsorption capacity and selectivity for CF4, respectively, which is superior to carbon nanoscrolls at 9.33 mmol/g and 5.1. These results outperform other porous materials, indicating that BN nanoscrolls are highly promising for CF4 capture.

Molecular structure characterization of middle-high rank coal via 13C NMR, XPS and FTIR spectroscopy

Elemental analysis, 13C nuclear magnetic resonance (NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), combined with Grand Canonical ensemble Monte Carlo (GCMC) simulations and energy minimizations were used to establish the molecular structure model of middle-high coal rank accurately. The three-dimensional molecular structure models of middle-high coal rank (from the No. 6 Mine of Pingdingshan (PDS) Mining Area and the No. 4 Mine of Hebi (HB) Mining Area in Henan Province, Xiegou (XG) Mine, Changping (CP) Mine, and Sihe (SH) Mine in Shanxi Province, China) were optimized and constructed. The results showed that the structural arrangement is more orderly and compact with the increase of coal rank. The established molecular formulae for PDS, HB, XG, CP, and SH are respectively C69H43NO3, C166H93N3O8, C191H125N3O7, C169H105N3O7, and C221H123N3O7.

Lithium decoration of boron-doped hybrid fullerenes and nanotubes as a novel 3D architecture for enhanced hydrogen storage: A DFT study

A three dimensional (3D) dumbbell-like nanostructure composed by interconnected fullerenes and nanotubes with Lithium decoration and boron-doping (37Li@C139B31) has been proposed in virtue of density functional theory (DFT) and first-principles molecular dynamics (MD) simulations which shows excellent geometric and thermal stability. First-principles calculations are performed to investigate the hydrogen adsorption onto the 37Li@C139B31. The results indicate that B substitution can improve the metal binding and the average binding energy of 37 adsorbed Li atoms on the C139B31 (2.79 eV) is higher than the cohesive energy of bulk Li (1.63 eV) suppressing the clustering. Meanwhile, the H2 storage gravimetric density of 178H2@37Li@C139B31 reaches up to 15.9 wt% higher than the year 2020 target from the US department of energy (DOE). The average adsorption energy of H2 molecules falls in a desirable range of 0.18–0.27 eV. Moreover, grand canonical ensemble Monte Carlo (GCMC) simulations reveal that at room temperature the hydrogen gravimetric density (HGD) adsorbed on 37Li@C139B31 reaches up to 11.6 wt% at 100 bars higher than the DOE 2020 target. Our multiscale simulations indicate that our proposed nanostructure provides a promising medium for hydrogen storage.

Capture of CO2 in carbon nanotube bundles supported with room-temperature ionic liquids: A molecular simulation study

Novel gas adsorption properties by room-temperature ionic liquids (ILs) confined in carbon nanotube (CNT) bundles were ascertained using grand canonical ensemble Monte Carlo (GCMC) simulations in which the adsorption and separation of CO2 from CO2/N2 mixtures. The introduction of ILs into the CNT channels significantly enhances the adsorption of CO2, while it is not sensitive to N2 adsorption. This is due to the strong interaction between specific ILs in the CNTs and CO2 molecules. The presence of water showed a significant impact on the adsorption capacity of CO2 as well.

All-silica zeolites screening for capture of toxic gases from molecular simulation

Abstract The exhaust gases, including SO2, NH3, H2S, NO2, NO, and CO, are principal air pollutants due to their severe harms to the ecological environment. Zeolites have been considered as good absorbent candidates to capture the six exhaust gases. In this work, we performed grand canonical ensemble Monte Carlo (GCMC) simulations to examine the capability of 95 kinds of all-silica zeolites in the removal of the six toxic gases, and to predict the adsorption isotherms of the six gases on all the zeolites. The simulation results showed that, H2S, NO, NO2, CO and NH3 are well-captured by zeolite structures with accessible surface area of 1600–1800 m2·g− 1 and pore diameter of 0.6–0.7 nm, such as AFY and PAU, while SO2 is well-adsorbed by zeolites containing larger accessible surface area (1700–2700 m2·g− 1) and pore diameter (0.7–1.4 nm) at room temperature and an atmospheric pressure. However, at saturated adsorption, zeolites RWY, IRR, JSR, TSC, and ITT are found to exhibit better abilities to capture these gases. Our study provides useful computational insights in choosing and designing zeolite structures with high performance to remove toxic gases for air purification, thereby facilitating the development and application of exhaust gas-processing technology in green industry.

Thiophene Separation with Silver-Doped Cu-BTC Metal–Organic Framework for Deep Desulfurization

Molecular simulations using grand-canonical ensemble Monte Carlo (GCMC) and first-principles calculations were performed to study the silver doped copper(II) benzene-1,3,5-tricarboxylate (Cu-BTC) metal organic framework (MOF) for deep desulfurization. The density function theory (DFT) calculations were conducted to quantify the binding energies of silver dopant with Cu-BTC as well as adsorbates. The computed DFT potentials were taken to parametrize the classical host–guest force fields for GCMC simulations with high accuracy. Adsorption isotherms of thiophene and toluene in isooctane solutions were experimentally measured using pure Cu-BTC samples for the validation of molecular modeling. The simulation results show that the doping of silver leads to significant increase of adsorption uptakes for all components (thiophene, toluene, and isooctane), agreeing with the results of calculated adsorption enthalpies in Ag-Cu-BTC. Simulation snapshots reveal that thiophene is preferentially accommodated in the sma...

Adsorption and Separation Mechanism of Thiophene/Benzene in MFI Zeolite: A GCMC Study

Selective removal of thiophene from aromatic components is one of the key challenges facing the petrochemical industry. The adsorption and separation mechanism from the molecular viewpoint can guide and upgrade the relative adsorption based technology. Therefore, we performed the grand canonical ensemble Monte Carlo (GCMC) simulation to investigate the adsorption performance and mechanism of competitive adsorption. Density distribution and radial distribution functions (RDF) analysis give a more detailed description of the adsorption sites. For pure component adsorption, donut-shaped adsorption sites were obtained for both benzene and thiophene from the straight channel point. From the viewpoint of the zigzag channel, the sorbates follow the straight line shape distribution at low loading and the S shape distribution at high loading. As for the binary component adsorption, more benzene adsorbs in the zeolite than thiophene at low pressure; however, thiophene competes successfully at high pressure. This ca...

Boron-substituted graphyne as a versatile material with high storage capacities of Li and H2: a multiscale theoretical study

Based on density functional theory (DFT), first-principles molecular dynamics (MD), and the grand canonical ensemble Monte Carlo (GCMC) method, we investigated the boron substitution in aromatic rings of graphyne in terms of geometric and electronic structures as well as its bifunctional application including Li and H2 storage. The calculated binding energies of B-doped graphyne (BG) are significantly enhanced at two adsorptive sites compared to pristine graphyne, leading to high lithiation potentials of 2.7 V in 6Li@1BG, and even higher with 3.0 V in 6Li@3BG. Thus, 6Li@1BG with a capacity of 1125 mA h g(-1), which is much larger than other carbon materials, is proposed to be a good anode material in lithium-ion batteries. For further hydrogen storage in 6Li@nBG, the results show that it can steadily adsorb at least 8H2 in DFT, MD and GCMC computations, and the excess gravimetric H2 uptake is 7.4 wt% at ambient conditions, exceeding the 2017 DOE target. Our multiscale simulations demonstrate that chemical modifications in two-dimensional carbon structures are very promising for high lithium storage and hydrogen uptake.

Si-doping effect on the enhanced hydrogen storage of single walled carbon nanotubes and graphene

We identified several parameters that correlate with the hydrogen physisorption energy and physicochemical properties of heteronuclear bonding in single-walled carbon nanotubes (SWCNT) and graphene. These parameters were used to find the most promising heteronuclear doping agents for SWCNTs and graphene for enhanced hydrogen storage capacity. Si-doping was showed to increase the amount of physisorbed hydrogen on such surfaces. Grand Canonical Ensemble Monte Carlo (GCMC) simulations showed that the hydrogen storage capacity of 10 at% Si-doped SWCNT (Si-CNT10) could reach a maximum of 2.5 wt%, almost twice the storage capacity of undoped SWCNTs, which were showed to reach a maximum capacity of 1.4 wt% at room temperature. To achieve this capacity, debundling effects of the uneven surfaces of Si-doped SWCNTs were found to be necessary. Similarly, 10 at% Si-doping on graphene (Si-GR10) was showed to increase the hydrogen storage capacity from 0.8 to 2.4 wt%.

Optimaization of Single-Walled Carbon Nanotube for Adsorption of Methane

In this paper, methane adsorption in single-walled carbon nanotube (SWNT) has been simulated by using the grand canonical ensemble Monte Carlo (GCMC) method. Lennard-Jones (LJ) potential is used to represent the fluid-fluid interaction, Lennard-Jones potential and integral method are used to calculation of the potential between fluid molecules and carbon atoms, respectively. In the simulation, two methods of calculation of potential between fluid molecules and SWNT are compared. The potential calculated by the two methods are almost the same. Then the influence of diameter of SWNT on the usable capacity ratio (UCR) is analyzed, and the parameters of the SWNT which has the best adsorption performance at 300K is recommended under certain pressure.

Computer Simulation in Actived Carbon Pores for Methane Storage

In this paper, adsorption of methane in actived carbon pores has been simulated by using the grand canonical ensemble Monte Carlo (GCMC) method. In the simulation, Lennard-Jones (LJ) potential is used for represent the fluid-fluid interaction, and the 10-4-3 potential is used for represent the interaction between fluid molecules and a slit carbon wall. Firstly, the adsorption isotherms of methane in actived carbon pores and local density profiles of methane in slit pore are obtained. Then, the interaction energy of methane in slit carbon pores with nine different pore sizes is obtained. Finally, the temperature, pressures, pore sizes affect the adsorption amount was studied, respectively.

Computational Simulation of Methane Adsorption in Single-Walled Carbon Nanotube

In this paper, methane adsorption in single-walled carbon nanotube (SWNT) has been simulated by using the grand canonical ensemble Monte Carlo (GCMC) method. Lennard-Jones (LJ) potential is used to represent the fluid-fluid interaction, and integral method is used to calculation of the potential between fluid molecules and carbon atoms. In the simulation, adsorption isotherms of methane in the (15, 15), (20, 20), (25, 25) and (30, 30) SWNT are simulated.

Simulation of adsorption, diffusion, and permeability of water and ethanol in NaA zeolite membranes

Grand canonical ensemble Monte Carlo (GCMC) and equilibrium molecular dynamics (EMD) methods were employed to simulate the adsorption and diffusion of water and ethanol in NaA zeolite from 298 K to 423 K. Competitive adsorption was found for the water/ethanol mixture adsorbed in NaA zeolite. The molecular diffusion in zeolite channels is affected more strongly by operating temperature than adsorption. Permeation fluxes of pure water and ethanol through a NaA zeolite membrane were predicted based on the simulated data of adsorption and diffusion. The contributions of adsorption and diffusion to the permeation flux were evaluated. The increased diffusivity at the elevated temperature is the main contributor to the improvement of the water permeation flux.

Structural properties of effective potential model by liquid state theories

This paper investigates the structural properties of a model fluid dictated by an effective inter-particle oscillatory potential by grand canonical ensemble Monte Carlo (GCEMC) simulation and classical liquid state theories. The chosen oscillatory potential incorporates basic interaction terms used in modeling of various complex fluids which is composed of mesoscopic particles dispersed in a solvent bath, the studied structural properties include radial distribution function in bulk and inhomogeneous density distribution profile due to influence of several external fields. The GCEMC results are employed to test the validity of two recently proposed theoretical approaches in the field of atomic fluids. One is an Ornstein-Zernike integral equation theory approach; the other is a third order + second order perturbation density functional theory. Satisfactory agreement between the GCEMC simulation and the pure theories fully indicates the ready adaptability of the atomic fluid theories to effective model potentials in complex fluids, and classifies the proposed theoretical approaches as convenient tools for the investigation of complex fluids under the single component macro-fluid approximation.

Adsorption of thiophene and benzene in sodium-exchanged MFI- and MOR-type zeolites: A molecular simulation study

The Grand Canonical ensemble Monte Carlo (GCMC) simulations were performed for studying the adsorption of thiophene and benzene in MFI- and MOR-type zeolites with various non-framework sodium atoms and framework aluminum densities. The computed adsorption isotherms are in good agreement with those obtained experimentally. The densities of the sodium and aluminum atoms in zeolite have a large influence on adsorption of thiophene and benzene. The GCMC simulations provide a better understanding of the effect of non-framework sodium atoms on the selective adsorption of binary mixtures of thiophene and benzene by these zeolite structures. The results show that increase of the non-framework sodium density in MFI-type zeolites increasingly blocks the intersections and thereby decreases the selectivity of MFI-type zeolites for adsorption of thiophene. By contrast, increasing the non-framework sodium density in MOR-type zeolites increases the number of sites favorable for adsorption of thiophene.

Prediction of adsorption of small molecules in porous materials based on ab initio force field method

Computational prediction of adsorption of small molecules in porous materials has great impact on the basic and applied research in chemical engineering and material sciences. In this work, we report an approach based on grand canonical ensemble Monte Carlo (GCMC) simulations and ab initio force fields. We calculated the adsorption curves of ammonia in ZSM-5 zeolite and hydrogen in MOF-5 (a metal-organic-framework material). The predictions agree well with experimental data. Because the predictions are based on the first principle force fields, this approach can be used for the adsorption prediction of new molecules or materials without experimental data as guidance.

Modeling of methane permeation through a defective region in MFI-type zeolite membranes

Abstract Molecular modeling of methane permeation though silicalite membranes, including the intercrystalline region, was carried out. We focused on the effect of the intercrystalline region on sorption and diffusion properties. Molecular dynamics (MD) and grand canonical ensemble Monte Carlo (GCMC) simulations were performed to estimate the diffusion coefficient and adsorption parameters. The result of the MD calculation indicates that the intrinsic diffusivity of methane decreases by an order of magnitude due to the presence of the intercrystalline region, although the adsorption properties do not change except at higher pressure (> 2000 kPa) where the adsorption increased slightly. The estimated permeability using these parameters based on the combined method of molecular simulation and permeation theory agree well with experiments. These results indicate the importance of considering the effect of an intercrystalline region on the permeability in zeolite membranes.

Structure and Adsorption of A Hard-Core Multi-Yukawa Fluid Confined in A Slitlike Pore: Grand Canonical Monte Carlo Simulation and Density Functional Study

Because of the increasing interest in studying the phenomenon exhibited by charge-stabilized colloidal suspensions in confining geometry, we present a density functional theory (DFT) for a hard-core multi-Yukawa fluid. The excess Helmholtz free-energy functional is constructed by using the modified fundamental measure theory and Rosenfeld's perturbative method, in which the bulk direct correlation function is obtained from the first-order mean spherical approximation. To validate the established theory, grand canonical ensemble Monte Carlo (GCMC) simulations are carried out to determine the density profiles and surface excesses of multi-Yukawa fluid in a slitlike pore. Comparisons of the theoretical results with the GCMC data suggest that the present DFT gives very accurate density profiles and surface excesses of multi-Yukawa fluid in the slitlike pore as well as the radial distribution functions of the bulk fluid. Both the DFT and the GCMC simulations predict the depletion of the multi-Yukawa fluid near a nonattractive wall, while the mean-field theory fails to describe this depletion in some cases. Because the simple form of the direct correlation function is used, the present DFT is computationally as efficient as the mean-field theory, but reproduces the simulation data much better than the mean-field theory.