Solar-assisted photocatalytic water splitting using defective UiO-66 solids from modulated synthesis

Metal-organic frameworks (MOFs) are attracting increasing interests as photocatalysts for solar-driven hydrogen production from water. This paper reports on a comparative study of using either acetic acid (AA) or trifluoroacetic acid (TFA) as the representative UiO-66 organic modulators for synthesizing visible light responsive UiO-66(Zr)-X (X: NH2 or NO2) photocatalysts for water splitting. The results show that photocatalytic hydrogen generation from a water/methanol mixture can be improved by varying the nature and amount of the modulator employed to prepare the different UiO-66(Zr)-X (X: NH2 or NO2) solid derivatives. UiO-66(Zr)-NH2 was the most active photocatalyst, followed by UiO-66(Zr)-NO2, both prepared with 12 equivalents of AA with respect to the organic ligand. This UiO-66(Zr)-NH2 solid was more active than the parent MOF in photocatalytic overall water splitting (OWS) (H2 and O2 production of 450 and 160 µmol·g−1, respectively, in 5 h; apparent quantum yield (AQY) at 400 nm of 0.06