Water‐Cluster–Mediated Amorphous‐to‐Crystalline Transition Enables Scalable Fabrication of Stable Surfactant‐Free MOF Nanocatalyst

Metal-organic framework (MOF) nanocatalysts are promising for solar-to-chemical conversion but often suffer hydrolytic degradation, especially in surfactant-free, highly surface-active forms. Here, we report a dual-functional design that integrates amorphous nanostructuring with water-triggered self-coordinated crystallization to produce scalable, stable surfactant-free MOF nanocatalysts. An amorphous pyridyl-porphyrinic precursor is first prepared as hexagonal nanosheets via an ultrasonic-assisted process. Upon exposure to water, cyclic hexameric water clusters bind pyridyl sites and drive reorganization into a corner-sharing porphyrinic-hexagon 3D honeycomb lattice, yielding robust hexagonal nanorods. Confined water clusters stabilize the lattice for >2 months and generate a pronounced potential gradient that promotes charge separation. The resulting nanocatalysts achieve a hydrogen evolution rate of 223.81 mmol g^-1 h^-1, representing one of the better values reported for molecular photocatalysts. This work introduces water-cluster-induced amorphous-to-crystalline self-assembly as a versatile strategy for stabilizing surfactant-free MOF nanophotocatalysts.