Sub‐1 Å Precision Tuning Interlayer Spacing of Robust Graphene Oxide Membranes for High‐Selectivity Molecular Sieving

Abstract Graphene oxide (GO) membranes, featuring uniform interlayer nanochannels, hold substantial potential for molecular sieving in aqueous solutions. Effectively tuning the interlayer spacing of GO membranes without relying on specific external environments is crucial to achieving practical sieving of molecules with varying sizes, but it remains a challenge. Here, the utilization of the spontaneous chain‐stretching characteristic of hydrated calcium alginate (CaAlg) intercalated within GO membranes is reported to adjust the interlayer spacing precisely. CaAlg‐intercalated‐GO membranes exhibit linearly tunable interlayer spacing with sub‐1Å precision when the CaAlg content is controlled. These membranes both achieve high rejection of 99% for organic molecules and enable molecular sieving with exceptional selectivity (463 for molecules with a size difference of 1.9 nm and 70 for molecules with a size difference of only 0.5 nm). Even after dehydration and long‐term storage, CaAlg‐intercalated‐GO membranes can rapidly regulate the interlayer spacing in aqueous solutions and maintain consistent molecular separation performance. The membranes also show ultrahigh tensile strengths of up to 410 MPa due to the formation of coordination bonds, thereby exhibiting robustness against external damage and under cross‐flow filtration. This work opens a new avenue for developing robust GO membranes tailored for practical molecular sieving and other separation applications.