Leveraging Framework Dynamics: Solvent-Triggered Breathing in MOFs for Enhanced CO₂ Photoreduction

Integrating MOFs with dynamic responsiveness and molecular catalytic centers offers unprecedented opportunities for the development of intelligent photocatalytic systems. Nevertheless, precisely regulating the dynamic behavior of the frameworks to optimize catalytic performance remains a major challenge. In this work, we report a novel strategy for fine-tuning the photocatalytic CO₂RR performance of a pyridine-nickel-functionalized NH₂-MIL-53(Al), denoted as PyNi-MIL-53, through a solvent-induced "breathing effect". Our investigations reveal that the framework undergoes reversible "breathing" in different solvents, which significantly alters both its pore dimensions and internal microenvironment. This solvent-driven structural transformation directly modulates CO₂ adsorption capacity and the transport efficiency of photogenerated electrons to the Ni active sites. As a result, the photocatalytic CO₂RR activity and selectivity of PyNi-MIL-53 can be intelligently tuned simply by changing the solvent. When cyclohexanone is used as the solvent, the catalyst exhibits the highest activity, reaching 403.3 μmol g^-1 h^-1 of CO₂ to CO without the use of any photosensitizer. This study not only provides a fresh "dynamic regulation" perspective for applying flexible MOFs in photocatalysis but also opens up new avenues for the design of next-generation smart responsive catalytic materials.