Robust photocatalytic reduction of Cr(VI) on UiO-66-NH2(Zr/Hf) metal-organic framework membrane under sunlight irradiation

The removal of toxic hexavalent chromium (Cr(VI)) ions from surface and ground water is highly demanded. While photocatalytic reduction of Cr(VI) to Cr(III) by traditional powder photocatalysts is a promising method, the difficult in the separation of the photocatalysts from the water hinders their wide practical applications. Herein we present the use of metal-organic framework (MOF) UiO-66-NH2(Zr/Hf) membrane as photocatalysts to reduce Cr(VI) ions with high efficiency and easy separation from the treated waste water. The UiO-66-NH2(Zr/Hf) MOF membrane photocatalysts were fabricated via a reactive seeding method on a alpha-Al2O3 substrate. It was found that the UiO-66-NH2(Zr/Hf) membranes exhibited excellent photocatalytic Cr(VI) reduction performance under both simulated and real sunlight irradiation. The UiO-66-NH2(Zr) membrane can maintain more than 94% Cr(VI) reduction efficiency after 20 cycles because of its exceptional chemical and water stability. The influences of foreign ions on Cr(VI) reduction were investigated to mimic real lake water, which revealed that no obvious adverse effects can be found with the presence of common foreign ions in surface water. The MOF membrane photocatalysts provide a new approach to carry out efficiently photocatalytic removal of pollutants in wastewater.