Photocatalytic pathway on the degradation of methylene blue from aqueous solutions using magnetite nanoparticles

In this work, magnetite nanoparticles, synthesized by the sol-gel citrate-nitrate method, were applied as precursors for methylene blue degradation in a simulated aqueous solution. The degradation pathway analysis was performed through a 22 experimental design, which includes nanoparticles and H2O2 concentration as variables. Statistical analysis showed that the nanoparticle concentration is the parameter with the greatest significance. The experiment conducted with the highest concentrations of nanoparticles and H2O2 (2250 mg/L and 130 g/L, respectively) obtained the most effective color removal (93.4%) in 210 min. Time-depended photodegradation was monitored by liquid chromatography coupled to tandem mass spectrometry. In addition, it was possible to suggest that different reaction mechanisms, such as Fenton reaction, photocatalysis, and adsorption, may contribute to the decrease in the concentration of methylene blue in the solution. The dye degradation kinetic data were adjusted by the adapted models of pseudo-first-order and pseudo-second-order. The results showed that the presence of the optimized magnetic nanoparticles powder led to a decrease of 148 times in the degradation concentration of methylene blue after 210 min of irradiation. In addition, the analysis of decomposition products showed that mineralization had advanced extensively to simple organic acids, showing the excellent performance of this photocatalytic system.