Secondary growth enables post-healing of stress-induced cracks in 2D Zr-MOF membrane for enhanced water purification

A controllable secondary growth repairs stress cracks in MOF membranes. • Capillary-driven precursors enable in situ nucleation and epitaxial crack healing. • Post-healing generates dense, crack-free, hydrophilic and charged layers. • Repaired membranes achieve high rejection and ultrahigh water flux simultaneously. • XDLVO analysis shows that repulsive interactions improve membrane antifouling. Metal–organic framework nanosheet membranes are promising for next-generation separations but remain limited by stress-induced cracking during fabrication and operation, which compromises structural integrity and separation reliability. Here we report a secondary growth strategy to heal cracks in membranes assembled from two-dimensional Zr-MOF nanosheets while enhancing structural robustness and separation performance. Capillary forces draw precursor solutions containing metal ions and organic linkers into preexisting stress-induced cracks. The subsequent secondary growth infills these defects, healing the cracked regions and restoring a dense, continuous selective layer. This post-fabrication repair strengthens intercrystalline connectivity without introducing thick sealing layers that impede water transport, thereby recovering both high solute rejection and permeability. Crack healing and membrane densification are achieved at an optimal nanosheet loading, whereas excessive loading leads to stress accumulation and renewed structural instability. The optimized membranes exhibit a continuous crack-free selective layer with increased thickness, enhanced hydrophilicity, and a higher negative surface charge. Compared with the primary Zr-MOF membrane (P-Zr-MOF), the repaired membrane (SG-Zr-MOF) achieves a tannic acid rejection of 96.8% with a water flux of 481.9 L m −2  h −1  bar −1 , together with improved mechanical flexibility and antifouling performance. This strategy couples defect repair with performance enhancement and provides a practical route for developing stable and efficient MOF membranes for sustainable water treatment. Download: Download high-res image (190KB) Download: Download full-size image