Comparison of different α-Fe2O3 sources in the enhancement of ZnO photocatalytic activity during the degradation of a mixture of endocrine-disruptors

Abstract

α-Fe₂O₃/ZnO composites were synthesized using MOF235(Fe), NH₂–MOF235(Fe), and FeOOH as α-Fe₂O₃ precursors via microwave-assisted precipitation and post-calcination at 450 °C. Thermogravimetric analyses (TGA), X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), N₂ physisorption analysis, scanning electron microscopy using a fully integrated EDS detector (SEM–EDS), X-ray photoelectron spectroscopy (XPS), and electrochemical experiments were employed to characterize the prepared materials. The coupling of MOF235(Fe)-, NH₂–MOF235(Fe)-, and FeOOH-derived α-Fe₂O₃ into ZnO increased the specific surface area values and light absorption in the visible region of ZnO. The NH₂–MOF235(Fe)-derived α-Fe₂O₃/ZnO allowed enhanced photogenerated charge separation with retarded e⁻/h⁺ recombination rate and reduced charge-transfer resistance, promoting superior photocatalytic activity. The photocatalytic activity of α-Fe₂O₃/ZnO composites was evaluated in the degradation of bisphenol A, 4-tert-butylphenol, and 4-tert-octylphenol mixture solution at pH 7.0 under simulated solar light using 0.5 g L⁻¹ catalyst loading. The mineralization percentages of endocrine-disrupting compounds (EDCs) of 36.76%, 42.25%, and 19.92% occurred in 330 min (600 kJ m⁻² of accumulated energy) for MOF235(Fe)-, NH₂–MOF235(Fe)-, and FeOOH-derived α-Fe₂O₃/ZnO, respectively. The QSAR approach using the ECOSAR program to evaluate the acute toxicity of the by-products generated with the NH₂–MOF235(Fe)_α-Fe₂O₃/ZnO photocatalyst showed that the effluent was nontoxic for the three target trophic models (fish, Daphnia, and green algae). This result was consistent with those of the Vibrio fischeri bioluminescence inhibition assay, where the effluents using NH₂–MOF235(Fe)_α-Fe₂O₃/ZnO were classified as nontoxic. Thus, NH₂–MOF235(Fe) can be successfully used as an α-Fe₂O₃ precursor to generate an α-Fe₂O₃/ZnO composite, which is a promising material for removing EDCs from aqueous solutions.