Sub-nm Pore Size Engineering in Metal–Phenolic Membranes

Metal-organic membranes with tunable nanopores provide a versatile platform for energy-efficient, high-precision separations. However, dynamic pore size engineering in the subnanometer (sub-nm) domain is challenging due to restricted control over bonding chemistry and coordination structures. Herein, we report a kinetic assembly strategy based on the oxidation-mediated coordination (OMC) of metal-phenolic networks (MPNs) that regulates ligand-metal bonding chemistry and directs mesoscale organization to afford precise and dynamic sub-nm control over pore size. The engineered MPN membranes undergo reversible, pH-induced coordination transitions, achieving a pore size engineering range of 0.73-1.43 nm (anodic aluminum oxide substrates), approximately two times wider than that reported for other dynamic nanofiltration membranes (typical range < 0.3 nm). Experimental results reveal that the OMC assembly strategy suppresses μ-hydroxo-bridged iron species and chelated water, thereby promoting uniform coordination environments and the formation of short- and medium-range domains that enhance the fidelity of coordination-state switching. Using a single membrane, multistage fractionation of organic dyes, lignin-derived monomers and trimers, and ultrasmall nanoparticles (0.2-3.0 nm) are achieved. This work demonstrates that kinetic assembly is a powerful approach to control dynamic coordination networks, advancing the structural control and functional adaptability of MPNs in controlled separation and stimuli-responsive applications.