Low-cost nanoparticulate oxidation catalysts for the removal of azo and anthraquinic dyes

Abstract

Purpose This study aimed to test the activity of Mn ferrite, hematin-Mn ferrite and colloidal maghemite in decomposition ofOrange II (O-II) and Alizarin Red S (ARS) in model aqueous solutions.Methods Color removal was explored at room temperature using magnetic stirring with and without a magnetic bar, takingadvantage of the solids? magnetism. Decomposition of H2O2 was also studied separately and as radicals provider in dyedecomposition. Catalyst/dye solution was fixed at 10 mg/4 mL. pH and dye concentration were variable. Absorbance wasmeasured during 120 min by UV-Vis. Reuse of catalysts was also performed.Results Azo dyes such as O-II are more resistant to oxidative removal using hydrogen peroxide than anthraquinone-like ARS.CITMD5 reduced ARS absorbance up to 71.9% when dye was less than 250 mg/L. HEM-Mn-MAG completely decolorized a62.5 mg/L O-II solution at pH 11 while CITMD5 reached half of that conversion under the same conditions. The highest colorremoval in O-II/ARS mixtures was obtained with HEM-Mn-MAG, 40% absorbance reduction in 2 h. Mn-MAG is not active toremove O-II in presence of hydrogen peroxide in the 3?9 pH range at rt.Conclusions The high activity of Mn-MAG in hydrogen peroxide decomposition may be assigned to the combination of Mn+2/Mn+3 and Fe+2/Fe+3, because theMnOx is active in the decomposition of hydrogen peroxide.Mn-MAGcan be reused, preservinghigh activity in this reaction. Mn-based magnetic nanoparticles should be considered as inexpensive materials to treat textilewastewaters.