Fabrication of Z-Scheme MIL-125/Ag/BiOBr Heterojunctions with Enhanced Photocatalytic Reduction of Cr⁶⁺

Herein, first, MIL-125 samples were synthesized via a hydrothermal method. Then, Ag species were doping on the surface of MIL-125 samples via the photolysis of silver nitrate. Finally, the Z-scheme MIL-125/Ag/BiOBr composite was synthesized via a directed liquid assembly method. The structure, morphology, and optical properties of the prepared samples were investigated via X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopic mapping, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, N₂ adsorption-desorption analysis, ultraviolet-visible spectroscopy, photoluminescence spectroscopy, surface photovoltage analysis, transient photocurrent response analysis, electrochemical impedance spectroscopy, and electron spin resonance analysis. Photocatalytic experiments indicated that the photocatalytic Cr⁶⁺ reduction efficiency of MIL-125/Ag/BiOBr heterojunctions was 85.7% at pH = 6, which was approximately 5.5 and 2.2 times higher than that using BiOBr and MIL-125 alone, respectively. This performance was attributed to the intimate interfacial contact between MIL-125 and BiOBr and the doping of Ag species, which increased the transfer and separation of photogenerated carriers and inhibited the recombination of electrons and holes. Furthermore, the possible photocatalytic Cr⁶⁺ reduction mechanism of the Z-scheme MIL-125/Ag/BiOBr photocatalyst was proposed.