Degradation of methylene blue dye under dark and visible light conditions in presence of hybrid composites of nanostructured MgFe2O4 ferrites and oxygenated organic compounds

Abstract

Nanostructured MgFe2O4 ferrites of crystallite sizes 7−16 nm synthesized by either autocombustion or polymerization methods were employed as catalysts in the degradation of methylene blue (MB) dye under dark and light irradiation conditions. The Mg-ferrites were characterized by XRD, atomic absorption, SEM, BET surface, thermogravimetric analysis, Mössbauer spectroscopy and magnetometry. All the catalysts can be described as hybrid composites of Mg-ferrites (with a 1:2 Mg:Fe ratio) and residual organic compounds coming from the precursors, whose band gap energy is in the visible region (Eg ∼ 2.3 eV). The magnetic responses at ambient temperature correspond to a soft material composed by the combination of superparamagnetic and blocked particle moments. The degradation of MB occurs under both dark and light conditions only when the catalyst is incorporated to the aqueous solution. The largest degradation efficiency percentages (PDE%) achieved after an interval of 35 min are around 60 and 75 % under dark and light conditions, respectively. In the presence of visible light, the efficiency of the catalysts is enhanced in a percentage that depends on the surface area of the ferrite particles. The role of organic residues as well as the exposed surface area in the catalytic process are analysed.