Co3O4@NH2-MIL-125(Ti) nanocomposites with crystal facet engineering for enhanced photocatalytic CO2 reduction

Engineering photocatalyst crystal facets and constructing heterojunctions are effective strategies to improve photocatalytic activity. The amino-modified titanium-based metal–organic framework (MOF) NH 2 -MIL-125(Ti) (NM) has drawn extensive attention as a photocatalyst by virtue of its high specific surface area, abundant pore structure, and narrow bandgap. However, its catalytic activity is hindered by fast electron-hole recombination and limited light absorption. This study synthesizes NM with engineered crystal facets and Co 3 O 4 @NH 2 -MIL-125(Ti) (C-NM) composites with varying Co 3 O 4 loadings using a facile hydrothermal method. The impact of heterojunctions and facet design on photocatalytic CO 2 reduction under visible light is also studied. Results show that the C-NM, with exposed {111} facets and optimal Co 3 O 4 loading, demonstrates superior photocatalytic CO and CH 4 production rates of 21.64 μmol h −1 g −1 and 3.99 μmol h −1 g −1 , 2.1 and 1.6 times higher than those of NM {001} , respectively. Experimental characterization and density functional theory (DFT) analyses attribute the improved photocatalytic activity to several mechanisms. First, crystal facet modulation can optimize the active sites and specific surface area of the photocatalysts. Second, by loading the narrow-bandgap Co 3 O 4 nanoparticles, bandgap of the C-NM photocatalyst is further reduced, thereby enhancing the absorption and utilization of visible light. Finally, the NM/Co 3 O 4 heterostructure minimizes electron-hole recombination, significantly boosting CO 2 reduction efficiency.