The Emergence of 2D Building Units in Metal-Organic Frameworks for Photocatalytic Hydrogen Evolution: A Case Study with COK-47

摘要

Metal-organic frameworks (MOFs) are promising materials for photocatalyticwater splitting reactions, but examples of visible light-responsive, catalyticallyactive, and stable MOFs are still rare. A detailed investigation is conducted forCOK-47 – a recently described MOF comprising 2D Ti-O_6 secondary buildingunits (SBUs) – toward a photocatalytic hydrogen evolution reaction (HER),showing how overall particle morphology, surface area, and missing liganddefects are central parameters governing the material’s ultimate performance.The newly synthesized COK-47_(ISO) is among the most active MOFs to date,yielding HER-rates of 8.6 μmol h~(?1), and an apparent quantum yield (AQY) of0.5 under visible light illumination. Optoelectronic and photoluminescenceinvestigations, supported by theoretical calculations, enable the unraveling ofits electronic structure along with charge transfer and recombination kinetics.A wavelength-dependent reaction mechanism is proposed involving ligand tometal charge transfer (LMCT) and the main challenges for visible or UVphotoexcitation are identified, demonstrating that the unique 2D layeredstructure aids charge separation and is key to the high performance. Thiswork introduces COK-47 as a promising alternative to the well-knownMIL-125 family and offers directions for future studies