Heidi C. Thiele

Metal-organic frameworks (MOFs) are regarded as promising materials for energy applications, particularly in photocatalytic hydrogen (H₂) production. This is due to their structural architectures that facilitate charge transfer, and tunable porous and light absorption properties. However, the many characteristics of MOFs including crystal morphology and sizes, surface facets, porosity, light absorption properties, and optical band gaps, can significantly influence their photocatalytic activity, presenting challenges in achieving reproducibility. In this study, we describe the synthesis of five distinct batches of the photoactive MOF, MIL-125-NH₂, utilizing different synthetic conditions. Solid-state characterization confirmed the purity, porosity, and light absorption properties of each MOF batch. Each material was then combined with nano sized Ni₂P as a cocatalyst, and their photocatalytic activity for H₂ evolution was evaluated. We observed variations in their photocatalytic H₂ evolution rates, which depended on the batch of MIL-125-NH₂ utilized, ranging from the lowest rate of 2980 μmol·h^-1·g^-1 to the highest of 4327 μmol·h^-1·g^-1. Notably, different H₂ evolution rates were also observed even when MIL-125-NH₂ was synthesized under identical synthetic conditions but by different students. Our research highlights the critical relationship between MOF synthesis parameters─such as reaction time, temperature, and precursor concentration─and resulting properties, including particle size, morphology, surface facets, and light absorption characteristics. These factors significantly influence their photocatalytic activity, as evidenced by varying H₂ evolution rates. This underscores the importance of optimizing materials synthesis conditions to improve reproducibility and efficiency in photocatalytic applications.