Application of Iron Oxides in the Photocatalytic Degradation of Real Effluent from Aluminum Anodizing Industries

This study reports the synthesis and evaluation of iron molybdate (Fe2(MoO4)3) and iron tungstate (FeWO4) as photocatalysts for the degradation of a real industrial effluent from aluminum anodizing processes under visible light irradiation. The oxides were synthesized via a co-precipitation method in an aqueous medium, followed by microwave-assisted hydrothermal treatment. Structural and morphological characterizations were performed using X-ray diffraction, field-emission scanning electron microscopy, Raman spectroscopy, ultraviolet–visible (UV–vis), and photoluminescence (PL) spectroscopies. The effluent was characterized by means of ionic chromatography, total organic carbon (TOC) analysis, physicochemical parameters (pH and conductivity), and UV–vis spectroscopy. Both materials exhibited well-crystallized structures with distinct morphologies: Fe2(MoO4)3 presented well-defined exposed (001) and (110) surfaces, while FeWO4 showed a highly porous, fluffy texture with irregularly shaped particles. In addition to morphology, both materials exhibited narrow bandgaps—2.11 eV for Fe2(MoO4)3 and 2.03 eV for FeWO4. PL analysis revealed deep defects in Fe2(MoO4)3 and shallow defects in FeWO4, which can influence the generation and lifetime of reactive oxygen species. These combined structural, electronic, and morphological features significantly affected their photocatalytic performance. TOC measurements revealed degradation efficiencies of 32.2% for Fe2(MoO4)3 and 45.3% for FeWO4 after 120 min of irradiation. The results highlight the critical role of morphology, optical properties, and defect structures in governing photocatalytic activity and reinforce the potential of these simple iron-based oxides for real wastewater treatment applications.