Incorporation anthracene and Cu to NH2-Zr-UiO-67 metal-organic framework: Introducing the simultaneous selectivity and efficiency in photocatalytic CO2 reduction to ethanol

Abstract

Metal-organic frameworks (MOFs) are considered promising candidates for photocatalytic CO2 reduction (PCR) into valuable organic fuels. However, compared to numerous reports regarding CO, CH4, and CHOOH generation, the explored MOFs have shown limited success in producing alcohols, particularly EtOH, through the PCR strategy. Existing MOFs also suffer from insufficient selectivity and efficiency. This study addresses these limitations by implementing a dual modification strategy on NH2-Zr-UiO-67 MOFs. This strategy involves synthesizing four MOF derivatives with different ratios of redox-active metal sites (Cu) to light absorption antenna (anthracene): 1:1, 2:1, 1:2, and 1:3. The as-synthesized MOFs (denoted as Cu/An (X:X)@NZU67 exhibited a remarkable capability for PCR-to-EtOH, without requiring a photosensitizer. The optimal amount of anthracene plays a crucial role in several aspects: improving light absorption, enhancing CO2 adsorption capacity, and promoting charge transfer/separation. Efficient charge transfer is critical for facilitating the multi-step electron transfer pathway required for ethanol synthesis. Notably, Cu/An (1:2)@NZU67 achieved an ethanol productivity of 624.17 µmolh−1g−1 for EtOH, which is, to the best of our knowledge, the highest efficiency reported for MOFs in PCR-to-EtOH conversion so far. Besides significant performance, the MOF showed 100% selectivity for EtOH production. This work represents a significant milestone in the field of PCR-to-EtOH transformation by providing a new perspective for designing MOF photocatalysts that can simultaneously improve both selectivity and efficiency.