Water Stable Zr-Benzenedicarboxylate Metal-Organic Frameworks as Photocatalysts for Hydrogen Generation

The Zr-containing metal-organic frameworks (MOFs) formed by terephthalate (UiO-66) and 2-amino-terephthalate ligands [UiO-66(NH2)] are two notably water-resistant MOFs that exhibit photocatalytic activity for hydrogen generation in methanol or water/methanol upon irradiation at wavelength longer than 300 nm. The apparent quantum yield for H-2 generation using monochromatic light at 370 nm in water/methanol 3:1 was of 3.5% for UiO-66(NH2). Laser-flash photolysis has allowed detecting for UiO-66 and UiO-66(NH2) the photochemical generation of a long lived charge separated state whose decay is not complete 300 mu s after the laser flash. Our finding and particularly the influence of the amino group producing a bathochromic shift in the optical spectrum without altering the photochemistry shows promises for the development of more efficient MOFs for water splitting.