Degradation and mineralization of methylene blue using a heterogeneous photo-Fenton catalyst under visible and solar light irradiation

Abstract

A SiO₂-supported Fe and Ni bimetallic catalyst has been synthesized, characterized and, for the first time, tested as a heterogeneous photo-Fenton catalyst for the degradation and mineralization of methylene blue (MB) dye. The morphological, structural, and optical properties of this catalyst were analyzed using FESEM, XRD, FTIR and UV–vis spectroscopy. The photocatalytic degradation of MB has been investigated using Fe–Ni/SiO₂ catalysts under visible and solar light irradiation in aqueous solutions. The effects of solution pH, H₂O₂ concentration, initial MB concentration, catalyst dosage and light intensity on the degradation of MB have been systematically investigated. An almost complete degradation was achieved within 60 min with a solution pH of 3.00, a H₂O₂ concentration of 3.0 mM L⁻¹ and a catalyst dose of 0.85 g L⁻¹. The degradation and total organic carbon (TOC) removal efficiencies were 99.80% and 86.19%, respectively, for sunlight. However, the values were only 99.01% and 75.71% for visible light. These results suggested that Fe–Ni/SiO₂ possesses significant catalytic activity, and the solar-Fenton process is a feasible method for degrading and mineralizing the MB dye compared with artificial visible light. The catalytic action is attributed to H₂O₂ and the formation of hydroxyl radicals (˙OH) by Fe(III) in Fe–Ni/SiO₂via the photo-Fenton reactions. Furthermore, we determined that the catalyst activity can be replicated in successive experiments without a significant decline in the Fe–Ni/SiO₂ and H₂O₂ processing efficiency under light irradiation. Our results will be useful for future improvement of active heterogeneous photo-Fenton catalysts for developing organic dye-containing wastewater treatments.