Fabrication and characterization of copper (II) oxide/iron (III) oxide thin film heterostructures for trace arsenic (III) removal in water

In this study, nano-heterostructures based on copper (II) oxide/iron (III) oxide (CuO/α-Fe₂O₃) thin films were fabricated by a dip-coating technique using aqueous solutions. The heterostructures were deposited on fluorine-doped tin oxide glass substrates varying the CuO film thickness. From a detailed characterization using Fourier transform-infrared and X-ray diffraction the formation of CuO (tenorite)/α-Fe₂O₃ (hematite) was demonstrated. Atomic force microscopy provided valuable information on the growth of α-Fe₂O₃ crystals in the heterostructure with a conical-shaped surface. Meanwhile, the field emission scanning electron microscopy cross-section images confirm the formation of well-defined CuO layers under the α-Fe₂O₃ layers. The optical band gap energies for the heterostructures obtained were estimated from the diffuse reflectance spectra and ranged from 1.41 to 1.51 eV. Photoluminescence analysis revealed an improved separation and faster transfer of photogenerated electrons and holes for the heterostructures. The removal arsenic from an aqueous solution was achieved through the direct adsorption for As(III) and visible light oxidation to As(V). An enhancement of removal efficiency of As(III) for the heterostructures fabricated compared to pristine oxides was obtained.