La-doped MIL-88B(Fe)–NH2: a mixed-metal–organic framework photocatalyst for highly efficient reduction of Cr(vi) in an aqueous solution

Abstract

With the aim to resolve the problem of water pollution, we herein propose a new photocatalyst based on metal–organic frameworks (MOFs), called La-doped MIL-88B(Fe)–NH₂ (MIL-88B((1 − x)Fe/xLa)-NH₂), which was designed and employed for the photocatalytic reduction of Cr(VI) in aqueous solutions. MIL-88B((1−x)Fe/xLa)-NH₂ materials with different x values were synthesized via a one-pot solvothermal method. Their characteristics were investigated using various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Brunauer–Emmett–Teller (BET) analysis, Fourier-transform infrared (FT-IR) spectroscopy and ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS). We found that compared to pristine MIL-88B(Fe)–NH₂ with a photocatalytic efficiency of 67.08, MIL-88B((1 − x)Fe/xLa)-NH₂ materials with x = 0.010, 0.025 and 0.050 exhibit excellent photocatalytic efficiencies reaching 88.21, 81.19 and 80.26%, respectively, after only 30 minutes of irradiation at a small catalyst dosage of 0.2 g L⁻¹. These La-doped MIL-88B(Fe)–NH₂ photocatalysts can work well under mild conditions (pH = 6). Furthermore, they are robust—can be recycled for at least four consecutive runs without any activity loss. This novel material is promising for the photocatalytic degradation of pollutants.