Defect-Tailoring and Titanium Substitution in Metal–Organic Framework UiO-66-NH2 for the Photocatalytic Degradation of Cr(VI) to Cr(III)

Defect engineering and surface chemistry are closely related to the performance of materials. In this work, the effects of Zr precursors and Ti substitution on the photocatalytic performance of UiO-66-NH2 are studied and analyzed from the perspective of defect engineering and surface chemistry. The findings show that when using ZrOCl2·8H2O as the Zr precursor combined with the postsynthetic treatment of Ti substitution, sample U-OCl-Ti shows significant improvement in Cr(VI) adsorption (20.9 mg/g) and photocatalytic reduction of Cr(VI) under visible light. The improvement can be attributed to the highly defective framework and more -NH2 groups exposed on the surface; therefore the highest light absorption and lowest recombination rate of photogenerated electron–hole pairs are observed in U-OCl-Ti. The findings in this study contribute to a better understanding of how defects and surface chemistry affect the photocatalytic performance, thus providing some designing knowledge for the synthesis of UiO-66 or UiO-66-NH2 with high photocatalytic performance.