Molecular Dynamics Simulations Of C0₂/N₂ Separation Through Two Dimensional Graphene Oxide Membranes

Carbon capture and storage?CCS?technology is one opinion for reducing anthropogenic CO₂ emissions.The captured CO₂ could also be reused in industry.The traditional methods of separation and capture are restricted by the cost and energy consumption,so the efficiency of separation is not satisfactory.The membrane separation has a promise in separating and capturing carbon dioxide due to its environmental friendly and ultra-thin.Graphene oxide has been attracted interests by scholars owe to low-cost and easily-prepared.There are two routes for gas separation.First,they pass through interedge gate to accomplish transmembrane transport.Then,the gas molecules traverse the interlayer space to realize interlayer transporting process.Understanding the migration behavior of gas molecule in these channels is crucial to comprehend the separation process,mechanism,and improving separation performance.The molecular dynamics simulation was adopted in our work to study the behavior of gas molecules.Our aim is to reveal gas separation mechanism from microcosmic perspective and the structure-function relationship between membrane structure and separation performance.First,in this study,MD simulations were conducted to investigate the permeability and selectivity of CO₂/N₂ passing through an interlayer channel of GO membrane(d=7.3?,R_O/C=30%).The GO exhibits excellent performance.CO₂ molecule could pass through the channel continuously,but N₂ could not.The preferential adsorption of CO₂ because of the modified groups was found to be responsible for the high selectivity and large permeability of CO₂ over N₂.The effects of oxidization degree and interlayer spacing were also investigated,and the high oxidization degree endows the channel with high selectivity and low permeability;meanwhile,the large interlayer spacing allows the channel to have large permeability and low selectivity.Furthermore,the channel length and temperature were found to be another factor influencing the gas transport performance.Next,the effects of membrane configurational parameters on the gas separation and mechanisms about CO₂/N₂ selective separation of bilayer GO sheets were studied and uncovered through molecular dynamics simulations.We can improve permeability and selectivity for different sizes of slit edge through regulating membrane configurational parameters.For selective smaller opening edge?6.0??,a membrane with the fully aligned slits is desirable.Furthermore,enlarging the interlayer space is another good choice.The small opening edge is the primary factor of selectivity,and permeations are due to both the width of slit edge and interlayer space.For the bigger opening edge?8.0??,which has lost selectivity itself,we can increase nanoslit offset to achieve well separation performance.The improved performances owe to the selectivity of long interlayer channel which gas molecules have to pass through.These results and findings are of great significance for the development of GO-based membrane.