Copper metallurgical slag as a sustainable precursor of iron oxide photocatalysts to remove indigo carmine dye from water using the photo-Fenton process

Abstract

The synthesis of an efficient composite photo-Fenton nanocatalyst was investigated using acid leaching processes of copper slag (CS) with two types of citric acid (EC = edible and AR = analytical-grade reagent). For this purpose, citric acid at room temperature or at 40 °C was used to lixiviate the elements from CS, and then, the leachates were subjected to a thermal treatment (350 °C). The formation of maghemite (γ-Fe₂O₃) accompanied with calcite as the main mineralogical phase was observed by X-ray diffraction (XRD) studies. The development of nanospheres dispersed in the calcite matrix and the proportion of γ-Fe₂O₃ in the catalyst or composite material were revealed by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively. The catalyst performance in the Fenton and photo-Fenton processes was investigated in the degradation of the indigo carmine dye (IC, 10 ppm), achieving an efficiency of 96.1 ± 2.1% in 60 min, using 5 mM of H₂O₂ (30% weight) and UV-light (λ = 365 nm). The activity of these materials was analyzed and compared as a function of the specific surface area and the % γ-Fe₂O₃ in the composites. The preparation of maghemite-rich nanocomposite using the CS leachate, generated with edible citric acid, is an excellent alternative to substitute materials produced with analytical grade reagents because in the removal of IC dye, it showed similar efficiency, kinetics, and stability, but with lesser requirements of lamp energy radiation and doses of photocatalyst and oxidant, with respect to data reported in the literature.