The separation of gases molecules with similar diameter and shape is an important area of research. For example, the major challenge to set up sweeping carbon dioxide capture and storage (CCS) in power plants is the energy requisite to separate the CO2 from flue gas. Porous graphene has been proposed as superior material for highly selective membranes for gas separation. Here we design some models of porous graphene with different sizes and shape as well as employ double layers porous graphene for efficient CO2/H2 separation. The selectivity and permeability of gas molecules through various nanopores were investigated by using the reactive molecular dynamics simulation which considers the bond forming/breaking mechanism for all atoms. Furthermore, it uses a geometry-dependent charge calculation scheme that accounts appropriately for polarization effect which can play an important role in interacting systems. It was found that H-modified porous graphene membrane with pore diameter (short side) of about 3.75 Å has excellent selectivity for CO2/H2 separation. The mechanism of gas penetration through the sub-nanometer pore was presented for the first time. The accuracy of MD simulation results validated by valuable DFT method. The present findings show that reactive MD simulation can propose an economical means of separating gases mixture.

Here, the adsorption behavior of the CO2 molecules on electronic properties of zigzag and armchair ZnO nanotubes (ZnONTs) has been studied at M06-2X/6-31G(d) level of theory. It is found that CO2 molecules can be physically adsorbed on the nanotubes. Two minima structures A (monodentate) and B (bidentate) were found on the potential energy surface. Inspection of the results shows that in zigzag and armchair nanotubes, the monodentate complex is more stable than bidentate complex. Also, the stability of complexes increases by increasing the number of CO2 molecules. Comparison of adsorption energies shows that adsorption of CO2 molecules over zigzag (6, 0) model is stronger than armchair (4,4) model. In this work, the various parameters such as electronic chemical potential (m), hardness (ƞ), softness (S), the maximum amount of electronic charge (DNmax), electrophilicity index (ω), dipole moment and work function were investigated to evaluate the reactivity of structures. It is predicted that the conductivity and reactivity of nanotubes increase upon complexation. Based on the natural bond orbital (NBO) analysis, in all complexes charge transfer occurs from CO2 molecules to the nanotube. Theory of atoms in molecules (AIM) was also applied to characterize OCO2… Zn interaction in nanotubes. In addition, the interaction strength is studied through the reduced density gradient (RDG) function. It is predicted that the ZnONTs can be introduced as a favorable candidate in the design and construction of sensors for detecting CO2 molecules.