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.
We use molecular dynamics (MD) simulations to show that a DNA-like double helix of two poly(acetylene) (PA) chains can form inside single-walled carbon nanotubes (SWNTs). The computational results indicate that SWNTs can activate and guide the self-assembly of polymer chains, allowing them to adopt a helical configuration in a SWNT through the combined action of the van der Waals potential well and the π-π stacking interaction between the polymer and the inner surface of SWNTs. Meanwhile both the SWNT size and polymer chain stiffness determine the outcome of the nanostructure. Furthermore, we also found that water clusters encourage the self-assembly of PA helical structures in the tube. This molecular model may lead to a better understanding of the formation of a double helix biological molecule inside SWNTs. Alternatively, it could form the basis of a novel nanoscale material by utilizing the 'empty' spaces of SWNTs.
The effect of functional groups on the radial collapse and elasticity of a single-walled carbon nanotube (SWNT) under hydrostatic pressure was investigated using molecular dynamics and molecular mechanics simulations. It is found that the radial collapse and elasticity of the chemically modified SWNTs strongly depend on the polarity of the functional groups and the degree of functionalization. The results show that the fluorine modified SWNT (F-SWNT), on which 2.5-5.0% of the atoms are attached to -F groups, can sustain the original elasticity of the intrinsic SWNT, and the pressure needed to collapse the F-SWNT increases by 11.3-21.8%. Functional groups such as hydroxyl groups, amino groups and carboxylic groups can increase the pressure needed to collapse the modified SWNTs, but decrease their radial elasticity. Therefore, the F-SWNTs, due to the higher collapse pressure, are ideal fillers for nanocomposites for high load mechanical support.
The collapse and stability of carbon nanotubes (CNTs) functionalized by corrosion inhibitor molecules on the Fe (1 0 0) surface were studied using molecular mechanics and molecular dynamics simulations. The results show that the pristine CNTs can approach and even collapse spontaneously onto the Fe surface due to the van der Waals force between them when the CNT diameter exceeds a certain threshold. To avoid collapse of the CNTs, they are randomly sidefunctionalized by three corrosion inhibitors. When the modification coverage exceeds 4.33%, these modified CNTs can basically maintain their cylindrical structures on the Fe surface. The CNTs, randomly modified by appropriate inhibitor groups, can maintain their cylindrical structure stably, giving them the potential to be used as nanocontainers for maintaining or transporting molecules, etc. Moreover, our findings have great practical significance, and CNTs modified by the organic inhibitor groups can be considered to be environmentally-friendly corrosion inhibitors, which can provide some guidance towards understanding corrosion resistance of CNT-inhibitor composites.
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