In Situ Growth of Ti3C2/UiO-66-NH2 Composites for Photoreduction of Cr(VI)

Cr(VI) is one of the most toxic heavy metals, posing multiple threats to humans and ecosystems. Photoreduction of toxic Cr(VI) to para-toxic Cr(III) is one of the most effective ways to remove heavy metal chromium but is still challenging. Herein, Ti3C2/UiO-66-NH2 composites with different ratio of Ti3C2 were synthesized via an in situ solvothermal process and used for the enhanced photocatalytic removal of Cr(VI) for the first time. The UiO-66-NH2 nanoparticles were dispersed on the surface and slits of accordion-like Ti3C2 homogeneously. A strong interfacial interaction between Ti3C2 and UiO-66-NH2 was formed, which was indicated by the XPS. The Fermi level of the MXene cocatalyst is lower than UiO-66-NH2; thus, Ti3C2 can serve as the electron sink and accumulate photogenerated electrons from UiO-66-NH2 on its surface. A depletion layer was also formed due to the different Fermi levels of UiO-66-NH2 and Ti3C2, which prevents electrons from flowing back to UiO-66-NH. The strong interfacial interaction and formed depletion layer are beneficial for the following charge transfer from UiO-66-NH2 to Ti3C2 after light irradiation and for suppressing the photogenerated charge recombination. With suitable band positions and enhanced charge separation ability, Ti3C2/UiO-66-NH2 composites exhibited better photoreduction efficiency of Cr2O72− than pure Ti3C2 and UiO-66-NH2, with optimized samples reaching 100% in 40 min. The photoreduction kinetics of Cr2O72− by 2-T/U was also studied, with a photoreduction rate of 0.0871 min−1, which is about 2.6 times higher than that of the pure UiO-66-NH. This research provides a new type of efficient and environmentally friendly photocatalysts for the photoreduction of Cr2O72−.