Amine Functionalized Metal-Organic Framework Coordinated with Transition Metal Ions: d-d Transition Enhanced Optical Absorption and Role of Transition Metal Sites on Solar Light Driven H2 Production.

Design and development of efficient photocatalysts for H2 production from water and sunlight have gained significant attention as the solar assisted approach is considered to be a promising approach for the generation of clean fuel. However, the poor charge carrier separation and light harvesting ability of existing photocatalysts limits the efficiency of photoconversion of water. In this work, the synthesis of transition metal ions (M2+ = Co2+ , Cu2+ , and Ni2+ ) coordinated with Ti-metal organic frameworks (Ti-MOFs) through a simple post-synthetic coordination method for efficient solar light-driven H2 production is reported. Notably, coordination of M2+ ions with Ti-MOF significantly improves the optical absorption by d-d transitions and the multimetal sites facilitate the fast charge carrier separation, thereby enhancing the solar light-driven H2 production activity. Very interestingly, the rate of solar light-driven H2 production is varied with respect to different metal ions coordination due to the position of d-d bands absorption in the solar spectrum, and the complexing tendency of M2+ ions with sacrificial electron donors. A maximum solar H2 production rate of 1583.55 µmol h-1 g-1 is achieved with a Cu2+ coordinated Ti-MOF, which is ≈13 fold higher than that of the pristine Ti-MOF.