Enhancing visible-light photocatalytic activity for overall water splitting in UiO-66 by controlling metal node composition

The photocatalytic activity of a series of five UiO-66 (M: Zr, Zr/Ti, Zr/Ce, Zr/Ce/Ti, Ce) materials for overall water splitting with generation of hydrogen and oxygen has been herein measured. The most efficient photocatalyst for the overall water splitting is the trimetallic MOF UiO-66(Zr/Ce/Ti) which achieves 230 mu mol.g(-1) of H-2 and 110 mu mol.g(-1) of O-2, upon UV light irradiation, and 210 mu mol.g(-1) of H-2 and 70 mu mol.g(-1) of O-2, under visible light irradiation. These productivity data indicate that a considerable percentage of its photocatalytic activity derives from the visible region of the spectrum (lambda > 450 nm). The photocatalytic activity of trimetallic UiO-66(Zr/Ce/Ti) was maintained upon reuse. Kinetics of the charge separated state monitored by transient absorption spectroscopy shows similar deactivation profiles for the five UiO-66 samples, suggesting that it is the charge separation efficiency the main factor responsible for the differences in the photocatalytic activity. The use of methanol as sacrificial agent during the photocatalytic experiments indicated that the high photocatalytic efficiency for overall water splitting in UiO-66(Zr/Ce/Ti) derives from the favorable kinetics of oxygen evolution. These results show the potential of multimetallic metal-organic frameworks as solar photocatalysts by tuning light absorption towards the visible region.