Synthesis of Magnetic Modified Clays for the Removal of Methylene Blue from Aqueous Solutions by Catalytic Wet Peroxide Oxidation

The purpose of this work was to develop and study catalytically active magnetic composites based on natural clays of Kazakhstan for their use in the process of catalytic wet peroxide oxidation (CWPO) of organic dyes. The synthesized materials, MnFe2O4/Shymkent and MnFe2O4/Ural, were obtained by intercalation of Fe2+, Fe3+, and Mn2+ ions into the interlayer spaces of natural aluminosilicates followed by heat treatment at 500 °C. The phase composition, morphology, and functional groups of the studied samples were characterized by the methods of elemental composition, X-Ray phase analysis, scanning electron microscopy, IR Fourier spectroscopy, and thermogravimetric analysis. The catalytic activity of the modified clays was evaluated in the decomposition reaction of methylene blue (MB) using hydrogen peroxide. To identify the influencing factors, adsorption experiments were conducted, including studying the effect of the adsorbent dose, the effect of pH on the degree of MB removal, and evaluating the activity of modified clays during the CWPO process under mild reaction conditions. The experiments were carried out at an initial dye concentration of C0 = 50 mg/L, a catalyst dose of 0.25, 0.5, and 2.5 g/L, pH = 3 and 6, and a temperature of 50 °C. It was found that the degree of MB removal in adsorption experiments reaches 70% at a dose of 0.25 g/L and increases to 97.8–99% at 2.5 g/L. In terms of CWPO, with the addition of H2O2 complete degradation of MB was achieved within 120 min for MnFe2O4/Shymkent and 150 min for MnFe2O4/Ural. The high efficiency of the modified clays is explained by the formation of the MnFe2O4 ferritic spinel structure, an increase in porosity, specific surface area and hydrophilicity, as well as an improvement in the acid-base properties of the surface. The TGA results showed an increase in the thermal stability and uniformity of the composites. Thus, the developed magnetic composites can be considered as promising materials for the effective removal of organic pollutants from wastewater under mild CWPO conditions.