lenge for 2D-material membranes to separate mixtures of molecules with extremely close physical properties and kinetic diameters owing to the lack of size-sieving properties and specific affinity of the 2D nanochannels. For instance, towards ethylene/ethane separation, the current distillation technology is very energy-consuming and concurrently increases carbon dioxide emissions. [8] It is considered as one of the seven chemical separations that if improved can reap great global benefits. [9] The most widely investigated membrane material for ethylene/ethane separation is a carbon molecular sieve (CMS), which possesses ultramicropores with molecular sieving properties. [10] However, the relatively low mechanical strength and aging problem might restrict its development. An alternative is developing ethylene or ethane-selective adsorbent, [11] which is based on designing specific interactions towards targeted molecules. Until now, there is no reported membrane material having both molecular sieving and specific interaction properties for efficient ethylene/ethane separation. Molecular recognition is some of the most significant features of chemical and biological systems. [12] The recognition effect stems from specific noncovalent interactions, including hydrogen bonding, metal coordination, van der Waals forces, and π-π interactions. The most common recognition motif is between antibodies and aptamers, [13] where the key lies in a unique structure formed by a folded and constrained bioheteropolymer that creates a binding pocket/interface able to recognize a specific molecule. Such exquisite molecular complementarity between antibodies and aptamers inspires us to mimic their structure and feature to construct 2D channels with optimized geometry and chemistry configurations for gaining improved molecular discrimination properties.Herein, we design novel metal-confining 2D sub-nanometer channels with molecular recognition and precise size-sieving for discriminating ethylene over ethane (Scheme 1). Graphene oxide (GO) nanosheets are assembled into 2D channels with precisely controlled sub-nanometer interlayer height to discriminate planar ethylene (4.84 Å × 4.18 Å × 3.28 Å) over stereoscopic ethane (4.82 Å × 4.08 Å × 3.81 Å) by the size difference of 0.53 Å along the c axis (Figure S1 and Table S1, Supporting Membranes with nanochannels have exhibited great potential in molecular separations, while it remains a great challenge to separate molecules with very close physical properties and kinetic diameters (e.g., ethylene/ethane) owing to the lack of size-sieving property and specific affinity. Herein, a metal confined 2D sub-nanometer channel is reported to successfully discriminate ethylene over ethane via molecular recognition and sieving. Transition metal cations are paired with polyelectrolyte anions to achieve high dissociation activity, forming reversible complexation with ethylene. Aberration-corrected transmission electron microscopy observes that the metals with size of ≈2 nm are uniformly confined in graph...