A green synthesized recyclable ZnO/MIL-101(Fe) for Rhodamine B dye removal via adsorption and photo-degradation under UV and visible light irradiation

Metal-organic frameworks (MOFs) have recently debuted as participants and solid supports in catalysts for environmental application in water treatment. Visible light active nanocomposites; ZnO/MIL-101(Fe); were synthesized via a hydrothermal method by loading ZnO; prepared by a green method; on a porous MIL-101(Fe) to be used as a heterogeneous catalyst for Rhodamine B dye (RhB) degradation as a model pollutant. The effect of adding acetic acid during the preparation of MIL-101(Fe) was studied; [A] used for the samples prepared by acetic acid. The prepared catalysts were characterized by XPS, XRD, zeta potential, TGA, FTIR, N₂ adsorption-desorption measurements, SEM, EDX, elemental mapping, TEM, and UV-VIS diffuse reflectance spectroscopy. The loading of ZnO on MIL-101(Fe) decreased the band gap from 3.2 eV for ZnO to be 2.85 eV for ZnO/MIL-101(Fe)[A], this low band gap explaining the obtained high activity under visible light irradiation. The mechanism of the photocatalytic degradation of RhB was investigated by introducing different scavengers to compete for the possible reactive species involved in the degradation process. The trapping experiments indicated that h⁺ and ^•OH have a vital role in the RhB degradation. The reusability of MIL-101(Fe) was also investigated after three runs. Thus, the synthesized ZnO/MIL-101(Fe)[A] could be used as an alternative catalyst for the photocatalytic degradation of coloured wastewater as it can successfully degrade 97.1% of Rhodamine B (10 mg/L) with high reaction rate (k = 0.0339 min^-1) under visible light irradiation for 300 min using 0.5 g/L of the catalyst. The as-prepared ZnO/MIL-101(Fe) and ZnO/MIL-101(Fe)[A] have competitive photocatalytic dye degradation activity.