Novel Ag@NH₂-UiO-66(Zr) photocatalyst with controllable charge transfer pathways for efficient Cr(VI) remediation

Rational fabrication of core-shell photocatalysts to hamper the charge recombination is extraordinarily essential to enhance photocatalytic activity. In this work, core-shell Ag@NH₂-UiO-66 (Ag@NU) Schottky heterojunctions with low Ag content (1 wt%) were constructed by a two-step solvothermal method and adopted for Cr(VI) reduction under LED light. Typically, the one with the Ag: NH₂-UiO-66 mass ratio (1 : 100) led to 100% Cr(VI) removal within 1 h, superior to bare NH₂-UiO-66 and Ag/NH₂-UiO-66 (Ag was directly decorated on NH₂-UiO-66 surface). The enhanced photocatalytic activity was related to the migration of the electrons on the CB of NH₂-UiO-66 to Ag NPs through a Schottky barrier, and thus the undesired charge carriers recombination was avoided. This result was also evidenced by Density functional theory (DFT) calculations. The computational simulations indicate that the introduction of Ag effectively narrowed the band gap of NH₂-UiO-66, facilitating the transfer of photo-generated electrons, expanding the light absorption area, and significantly enhancing photocatalytic efficiency. Most importantly, such a core-shell structure can inhibit the formation of •O₂^-, letting the direct Cr(VI) reduction by photo-excited e^-. In addition, this structure can also protect Ag from being oxidized by O₂. Ten cyclic tests evidenced the Ag@NU had excellent chemical and structural stability. This research offers a novel strategy for regulating the Cr(VI) reduction by establishing core-shell photocatalytic materials.