Degradation and mineralization of methylene blue dye by peroxymonosulfate/Mn3O4 nanoparticles using central composite design: Kinetic study

In this study, the Mn 3 O 4 nanoparticles ( Mn 3 O 4 NPs) were synthesized by chemical precipitation for peroxymonosulfate (PMS) activation. The physicochemical properties of the synthesized Mn 3 O 4 catalysts were measured by X-ray diffraction (XRD), Fourier transform infrared (FTIR), and scanning electron microscopy (SEM). To investigate the parameters affecting the methylene blue (MB) decolorization process (pH, dye concentration, Mn 3 O 4 dosage, and PMS concentration), and optimization of them, response surface methodology (RSM) with central composite design (CCD) was used. In order to evaluate the efficiency of the studied process in removing organic matter and intermediate products, chemical oxygen demand (COD) and total organic carbon (TOC) analyzes were performed in optimal conditions, respectively. Maximum MB decolorization (86.71%) was achieved at optimal condition, pH = 4, Mn 3 O 4 = 0.12 g, PMS = 0.94 g, initial MB dye concentration = 62 mg/L at a fixed time 20 min. Experiment results showed that PMS generates sulfate radicals ( S O 4 ∙ - ) in the presence of Mn 3 O 4 NPs, which has a high ability to decompose refractor organic contaminants. According to the results, the highest catalytic performance of the MB decolorization mechanism is typically related to the synergistic effects of Mn 3 O 4 and PMS.