Dual-Ligand Ti-MOFs with Push–Pull Effect for Photocatalytic H<sub>2</sub> Production
Xin Xin, Zhanfeng Zhao, Yao Chen, Jiangdan Tan, Yonghui Shi, Hanjie Ren, Dong Yang, Zhongyi Jiang
Abstract
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 NH2-MIL-125(Ti), a kind of Ti-based metal–organic framework (MOF), as the model system. The dual-ligand MOF, NH2/Cl-MIL-125, was designed and synthesized based on the Hammett constant (σm), in which −NH2 (σm = −0.16) and −Cl (σm = 0.37) were selected as the electron-pushing group and the electron-pulling group, respectively. Meanwhile, −CH3 (σm = −0.07, electron-pushing) and −H (σm = 0, neither electron-pushing nor electron-pulling) were selected as the reference groups to prepare NH2/CH3-MIL-125 and NH2/H-MIL-125, respectively, to validate the electron push–pull effect. NH2/Cl-MIL-125 (5.32 mmol g–1 h–1) exhibits a higher photocatalytic H2 evolution activity than single-ligand NH2-MIL-125 (1.93 mmol g–1 h–1), NH2/CH3-MIL-125 (4.45 mmol g–1 h–1), and NH2/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 −NH2 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.