Morphology Engineering of Zr–N MOFs for High-Efficiency Photocatalytic Hydrogen Evolution

Metal-organic frameworks (MOFs) show promise in photocatalytic hydrogen evolution due to their intrinsic porosity and structural tunability, but their performance is often limited by poor reactant diffusion and slow charge transfer. In this paper, we obtained the UiO-68-NH₂ (Zr-N) MOF with flake, octahedron, block, and flower morphologies in different sizes by adjusting the concentrations of acetic acid and water modulators. It is disclosed that the introduced acetic acid can compete with organic ligands for coordination with zirconium nodes, whereas water can affect the hydrolysis rate of zirconium precursors, thereby regulating the nucleation and crystal growth of the Zr-N crystals. Therefore, their synergistic effect led to the successful synthesis of Zr-N ions with different morphologies and sizes. Notably, the flower-like Zr-N with a size of about 100 nm and maximum specific surface area exposure of abundant active sites, which facilitates the diffusion of reactants as well as enhances the separation and transfer rate of photogenerated carriers, endowing it with excellent hydrogen evolution performance (989 μmol g^-1 h^-1) and being about 75 times higher than that of the bulk Zr-N counterpart (13 μmol g^-1 h^-1). This work validates the critical role of morphology engineering in advancing MOF-based photocatalysts for sustainable energy applications.