Robust Cr(VI) reduction over hydroxyl modified UiO-66 photocatalyst constructed from mixed ligands: Performances and mechanism insight with or without tartaric acid

Hydroxyl modified UiO-66 ((OH)(2)-UiO-66-X%, X represents the mass content ratio of introduced 2,5-dihydroxyterephthalic acid) was prepared via a solvothermal reaction between zirconium tetrachloride, benzene-1,4dicarboxylic acid (H2BDC), as well as 2,5-dihydroxyterephthalic acid (H2BDC-(OH)(2)). It was found that hydroxyl groups can act as the intramolecular hole scavenger to boost the photo-induced charge carrier separation to enhance Cr(VI) reduction. The photocatalytic Cr(VI) reduction activities of (OH)(2)-UiO-66-X% were investigated upon the irradiation of low-power ultraviolet LED light. The findings demonstrated that (OH)(2)-UiO-6620% with good cyclicity and stability exhibited superior photocatalytic performances to both UiO-66 and (OH)(2)UiO-66. The introduction of hydroxyl groups can also extend the light absorption region to longer wavelength in visible range, which provides possibility for displaying photocatalytic activities under sunlight. The effect of small molecule organic acid (SOAs), pH value, and co-existing inorganic ions on photocatalytic performances of (OH)2-UiO-66-20% were investigated. Tartaric acid (TA) as typical SOAs was introduced to the reaction system to further boost the photocatalytic Cr(VI) reduction via acting as hole scavenger, constructing charge-transfercomplex for quick electron transportation, and producing COO center dot(-) radicals. This work opened a new opportunity for modified MOFs for boosted elimination activities for environmental pollutants.

Automated summary

The study demonstrated that hydroxyl modified UiO-66 showed enhanced photo-induced charge carrier separation efficiency and improved Cr(VI) reduction activity. UiO-66 with 20% hydroxyl modification exhibited superior cyclic stability and photocatalytic performance compared to unmodified UiO-66 and UiO-66 with (OH)(2) modification. The introduction of hydroxyl groups extended the light absorption region to longer wavelengths in the visible range, potentially enabling photocatalytic activities under sunlight.