(380l) Tailoring Interlayer Spacing in Mxene/GO Composite Membranes for Enhanced Gas Separation Efficiency

Two-dimensional (2D) nanomaterial-based membranes have shown great potential for molecular separation owing to their attractive properties, including remarkable molecular sieving capabilities that offer an opportunity to overcome the inherent trade-off between permeability and selectivity¹. However, there are challenges in the use of 2D nanomaterials in membrane gas separation. These challenges include structural collapse, complex pore engineering, difficult exfoliation, and improper layer assembly.

MXenes, a novel family of 2D nanomaterials comprising transition metal carbides and nitrides, have found application across numerous domains due to their high aspect ratios, adjustable surface chemistry, and unique 2D lamellar structure². MXene membranes feature regular and aligned nanochannels, a result of surface terminations on the MXene surface, which hold promise for achieving significant improvements in gas separation performance³. Previous studies of pristine Ti₃C₂T_x MXene membranes have shown excellent gas permeance but limited selectivity of the membranes, caused by large interlayer spacing⁴ and the small size of Ti₃C₂T_x MXene flakes⁵ which negatively impact the flakes-alignment. Hence, developing the fabrication of 2D lamellar membranes with highly ordered nanolaminates for fast transportation and precise size-sieving ability remains challenging.

In this work, we introduce a novel highly permeable Ti₃C₂T_x MXene/graphene oxide (GO) composite membrane tailored for selective H₂ separation. Our preliminary results indicated that gas molecules with smaller kinetic diameters pass through the membranes more rapidly than those with larger kinetic diameters, indicating that molecular sieving dominates gas transport. Our hypothesis is that such a membrane possesses synergistic properties of both nanomaterials. More specifically, integrating larger GO flakes will not only effectively mask defects formed by Ti₃C₂T_x nanosheets but also enhance the molecular sieving capabilities of the membrane pathways, thereby improving selectivity. Given existing experimental evidence suggesting that combining GO with MXene leads to lower interlayer spacing⁶, the enhancement of separation properties observed in MXene/GO composite membranes supports our hypothesis. We perform gas permeation tests to investigate the transport behavior of gases, including H₂, CO₂, and CH₄. Additionally, we use various characterization techniques to evaluate the physicochemical properties of composite membranes that influence gas transport behavior. We conduct molecular dynamics (MD) simulations to study the gas transport through the membranes. Through this simulation, we determine potential mechanisms underlying the reduction of interlayer spacing, which may improve gas selectivity, thereby achieving a more favorable balance between permeability and selectivity. These combined experimental and theoretical studies are expected to shed light on the feasibility of finely adjusting interlayer spacing in the nanocomposite membranes to enhance molecular sieving for efficient gas separation.

References

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