Modulation of the charge transfer behavior of Ni(II)-doped NH2-MIL-125(Ti): Regulation of Ni ions content and enhanced photocatalytic CO2 reduction performance

Regulation of the electronic structure of metal oxo clusters in metal organic frameworks (MOFs) is a promising way to modulate charge transfer efficiency and photocatalytic performance. Herein, a series of Ni2+ doped NH2-MIL-125-Ti (NH2-MIL-125-Nix/Ti) with different Ni2+/Ti4+ molar ratio (x = 0.5%–1.5%) are prepared via an in-situ doping method. Correlations between the electronic structure of (Ti/Ni)8O8(OH)4 nodes and charge transfer efficiency, bandgap and energy position of band edges of the NH2-MIL-125-Nix/Ti are systematically investigated based on experimental and computational method. The doped Ni2+ was confirmed to be an efficient mediator to promote the electron transfer from photoexcited terephthalate ligand to the (Ti/Ni)8O8(OH)4 nodes in NH2-MIL-125-Nix/Ti. The NH2-MIL-125-Ni1%/Ti exhibited the highest CO2 conversion rate with 98.6% CO selectivity and the factors affecting the photocatalytic CO2 reduction performance are also studied. It provides some guidance for developing MOFs photocatalyst with targeted performance via modification of the electronic structure of metal oxo clusters.