Boosted Activity of g-C 3 N 4 /UiO-66-NH 2 Heterostructures for the Photocatalytic Degradation of Contaminants in Water.

The combination of graphitic carbon nitride and the metal-organic framework UiO-66-NH 2 has been developed with the aim to enhance the photocatalytic activity of pure semiconductors. Different proportions of g-C 3 N 4 and UiO-66-NH 2 were combined. Complete characterization analysis of the resulting photocatalytic materials was conducted, including N 2 adsorption isotherms, XRD, FTIR, STEM-EDX microscopy, DRS-UV-visible, and photoluminescence. The photocatalytic activity was tested in an aqueous solution for the removal of acetaminophen as the target pollutant. From the obtained results, less than 50% of UiO-66-NH 2 incorporated in the g-C 3 N 4 structure enhanced the photocatalytic degradation rate of both bare semiconductors. Concretely, 75% of g-C 3 N 4 in the final g-C 3 N 4 /UiO-66-NH 2 heterostructure led to the best results, i.e., complete acetaminophen elimination initially at 5 mg·L -1 in 2 h with a pseudo-first order rate constant of ca. 2 h -1 . The presence of UiO-66-NH 2 in the g-C 3 N 4 enhanced the optoelectronic properties, concretely, the separation of the photo-generated charges was improved according to photoluminescence characterization. The better photo-absorption uptake was also confirmed by the determination of the quantum efficiency values of the heterostructure if compared to either pure g-C 3 N 4 or UiO-66-NH 2 . This photocatalyst with the best activity was further tested at different pH values, with the best degradation rate at a pH close to the pH pzc ~4.15 of the solid. Sequential recycling tests demonstrated that the heterostructure was stable after five cycles of use, i.e., 15 h. A high contribution of photo-generated holes in the process of the degradation of acetaminophen, followed marginally by superoxide radicals, was suggested by scavenger tests.