Meixia Shan

Influence of chemical functionalization on the CO2/N2 separation performance of porous graphene membranes

The separation of CO₂ from a mixture of CO₂ and N₂ using a porous graphene membrane was investigated using molecular dynamics (MD) simulations. The effects of chemical functionalization of the graphene sheet and pore rim on the gas separation performance of porous graphene membranes were examined. It was found that chemical functionalization of the graphene sheet can increase the absorption ability of CO₂, while chemical functionalization of the pore rim can significantly improve the selectivity of CO₂ over N₂. The results show that the porous graphene membrane with all-N modified pore-16 exhibits a higher CO₂ selectivity over N₂ (∼11) due to the enhanced electrostatic interactions compared to the unmodified graphene membrane. This demonstrates the potential use of functionalized porous graphene as single-atom-thick membrane for CO₂ and N₂ separation. We provide an effective way to improve the gas separation performance of porous graphene membranes, which may be useful for designing new concept membranes for other gases.

Tunable Hydrogen Separation in Porous Graphene Membrane: First-Principle and Molecular Dynamic Simulation

First-principle density functional theory (DFT) calculation and molecular dynamic (MD) simulation are employed to investigate the hydrogen purification performance of two-dimensional porous graphene material (PG-ESX). First, the pore size of PG-ES1 (3.2775 Å) is expected to show high selectivity of H2 by DFT calculation. Then MD simulations demonstrate the hydrogen purification process of the PG-ESX membrane. The results indicate that the selectivity of H2 over several other gas molecules that often accompany H2 in industrial steam methane reforming or dehydrogenation of alkanes (such as N2, CO, and CH4) is sensitive to the pore size of the membrane. PG-ES and PG-ES1 membranes both exhibit high selectivity for H2 over other gases, but the permeability of the PG-ES membrane is much lower than the PG-ES1 membrane because of the smaller pore size. The PG-ES2 membrane with bigger pores demonstrates low selectivity for H2 over other gases. Energy barrier and electron density have been used to explain the difference of selectivity and permeability of PG-ESX membranes by DFT calculations. The energy barrier for gas molecules passing through the membrane generally increase with the decreasing of pore sizes or increasing of molecule kinetic diameter, due to the different electron overlap between gas and a membrane. The PG-ES1 membrane is far superior to other carbon membranes and has great potential applications in hydrogen purification, energy clean combustion, and making new concept membrane for gas separation.

Effect of defects on Young's modulus of graphene sheets: a molecular dynamics simulation

The effect of defects including vacancy and Stone–Wales (SW) defects on the Youngs modulus of graphene sheets is investigated using molecular dynamic (MD) simulations. The simulations show that the presence of defects reduces the Youngs modulus of graphene sheets and Youngs modulus decreases with increasing degree of defects. In addition, the vacancy defects bring about a decrease in the Youngs modulus, but their reconstruction is an important factor in stabilizing the modulus. Furthermore, we explore the Youngs modulus of graphene with defects functionalized by hydrogen atoms and find that the hydrogenation of vacancy defects can increase the Youngs modulus of the defective graphene but the hydrogenation of SW defects has the opposite effect.

Fullerene filling modulates carbon nanotube radial elasticity and resistance to high pressure

The high pressure behavior of carbon nanotubes (CNTs) filled with fullerenes (C60@CNTs) is investigated systematically using molecular mechanics and molecular dynamics simulations. It is shown that the C60 filling can increase the transition pressure (Pc) of intrinsic CNTs and optimize the radial elasticity of CNTs. The C60 filling increases the Pc of CNT(17, 0) by a factor of ∼25, and the Pc of CNT(10, 10) by a factor of ∼5. An inelastic CNT(17, 0) can be transformed into a superelastic CNT(17, 0) by filling C60 into CNTs. Moreover, C60@CNTs with larger diameters (21.76 A > d > 13.56 A) show the better radial elasticity compared with intrinsic CNTs. These characteristics can make C60@CNTs possess potential applications in pressure sensors, electromechanical oscillators, nanotube memory etc. In addition, C60@CNTs with larger diameters (21.76 A > d > 13.56 A) undergo two structure transitions under high pressure, which is well in agreement with the experimental results. The Lennard–Jones potential can describe the interaction between C60 and CNT well and explain radial collapse and recovery properties of C60@CNT completely, which can provide theoretical guidance for experimental results.