Hierarchically Porous Metal–Organic Framework Assembled by MOF-74-Ni Nanoparticles for Enhanced Photocatalytic CO2 Reduction

Metal–organic frameworks (MOFs) have emerged as pivotal materials for the photocatalytic reduction of CO2 to CO due to their exceptionally high surface areas and abundant active sites. However, most of the currently reported MOFs are confined to micropores (<2 nm), which limits adsorption/desorption and substance transport during photocatalytic CO2 reduction reactions. Herein, hierarchically porous MOFs (HP-MOF-74) were synthesized based on the assembly of MOF-74-Ni nanoparticles with different particle sizes (21, 42, and 85 nm) using spray-drying technology. The simultaneous enhancement of CO2 adsorption performance and photoelectroactivity was achieved in HP-MOF-74 due to the additional mesoporous structure formed by the nanoparticle stacking. The HP-MOF-74 exhibits 1.14–1.38 times improvement in the CO2 adsorption capacity compared to the corresponding initial MOF-74 nanoparticles (N-MOF-74). Meanwhile, the hierarchical architecture enhances photon utilization through improved light reflections and accelerates electronic transmission via additional mesopore pathways. These synergistic advantages collectively contribute to a 1.2–2.1 times enhancement in the CO generation rates of HP-MOF-74 compared with N-MOF-74 counterparts. Particularly, HP-MOF-74–42 nm demonstrated the highest CO production rate of 6.65 μmol h–1, outperforming most reported MOF-based photocatalysts. The construction of hierarchically porous MOFs provides a new idea for the design of highly efficient CO2 reduction photocatalysts.