Dual-Ligand Ti-MOFs with Push-Pull Effect for Photocatalytic H 2 Production.

Enhancing the photogenerated electrons transfer efficiency is crucial for photocatalytic reactions. Herein, a dual-ligand-induced push-pull effect was manipulated to intensify the transfer of photogenerated electrons between organic ligands and metal clusters using NH 2 -MIL-125(Ti), a kind of Ti-based metal-organic framework (MOF), as the model system. The dual-ligand MOF, NH 2 /Cl-MIL-125, was designed and synthesized based on the Hammett constant (σ m ), in which -NH 2 (σ m = -0.16) and -Cl (σ m = 0.37) were selected as the electron-pushing group and the electron-pulling group, respectively. Meanwhile, -CH 3 (σ m = -0.07, electron-pushing) and -H (σ m = 0, neither electron-pushing nor electron-pulling) were selected as the reference groups to prepare NH 2 /CH 3 -MIL-125 and NH 2 /H-MIL-125, respectively, to validate the electron push-pull effect. NH 2 /Cl-MIL-125 (5.32 mmol g -1 h -1 ) exhibits a higher photocatalytic H 2 evolution activity than single-ligand NH 2 -MIL-125 (1.93 mmol g -1 h -1 ), NH 2 /CH 3 -MIL-125 (4.45 mmol g -1 h -1 ), and NH 2 /H-MIL-125 (4.73 mmol g -1 h -1 ) under full-spectrum irradiation. The result can be attributed to the electron push-pull effect between -NH 2 and -Cl, which boosts the electron transfer along the ligand-metal-ligand direction. Our dual-ligand-induced push-pull strategy for enhancing the electron transfer may offer some novel insights into the rational design and synthesis of photocatalysts for many other reactions.