Using Electrolytic Manganese Residue to prepare novel nanocomposite catalysts for efficient degradation of Azo Dyes in Fenton-like processes

In this study, Electrolytic Manganese Residue (EMR) was treated by EDTA-2Na/NaOH, ultrasonic etching, and hydrothermal reaction to obtain a novel nanocomposite catalyst (called N-EMR), which then was used, together with H₂O₂, to treat synthetic textile wastewater containing Reactive Red X–3B, Methyl Orange, Methylene blue and Acid Orange 7. Results indicated that the N-EMR had a nano-sheet structure in sizes of 100–200 nm; new iron and manganese oxides with high activity were produced. The mixture of a small amount of N-EMR (40 mg/L) and H₂O₂ (0.4 × 10⁻³ M) could removal about 99% of azo dyes (at 100 mg/L in 100 mL) within 6–15 min, much faster than many advanced oxidation processes (AOPs) reported in the literature. The elucidation of the associated mechanism for azo dyes degradation indicates that azo dyes were attacked by superoxide radicals, hydroxyl radicals, and electron holes generated within system. N-EMR was found to be reusable and showed limited inhibition by co-existing anions and cations. Moreover, high removal efficiency of azo dyes could happen in the system with a wide range of pH (1–8.5) and temperatures (25–45 °C), indicating that the process developed in this study may have broad application potential in treatment of azo dyes contaminated wastewater.