A series of isostructural UiO-66-X (X = H, NH, Br, (OH), (SH)) catalysts have been successfully synthesized by modifying different functional groups on the ligand. The effects of the ligand modification of UiO-66 were investigated for their photocatalytic activity of Rhodamine B degradation under visible light. Surprisingly, UiO-66-NH and UiO-66-(OH) which have narrow bandgaps and excellent visible light absorption do not show outstanding photocatalytic performances compared to UiO-66 and UiO-66-Br. Electrochemical test results indicated that the conduction band potential of UiO-66-X and the separation efficiency of electrons were quite important in these photocatalytic reactions, other than the electronic effect as reported. Similar photocatalytic degradation behaviors were found for Congo red and methyl orange. Herein, we firstly reported different mechanisms of selective degradation in the case of UiO-66, which subverted the previous understanding of photodegradation behavior.

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Photocatalytic hydrogen production is an effective strategy for meeting energy challenges. Here, a composite for photocatalytic hydrogen production via introduction of UiO-66 nanospheres into flower-shaped ZnIn2S4 microspheres (ZIS/U6) is described. The optimum composite with 20 mg UiO-66 loading displayed the high photocatalytic rate of 1860.9 µmol g−1 h−1 with an apparent quantum efficiency of 1.4% at 420 nm under visible-light irradiation, which is nearly 3 times higher than that of ZnIn2S4. The improved photocatalytic H2 rate mainly benefited from effective electron transfer between ZnIn2S4 and UiO-66. Additionally, we tried to introduce UiO-66-NH2 and UiO-66-(SH)2 with excellent visible light absorption into ZnIn2S4 to obtain composites. Surprisingly, they did not exhibit better photocatalytic hydrogen production rates. Combined with the electrochemical test results, it was found that they had completely different electron transfer paths from ZIS/U6. Therefore, a different photocatalytic mechanism was proposed and further verified by transient photocurrent.

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