Preparation Of Core-shell Nano Zero Valent Iron And Manganese And Its Treatment Of Methylene Blue Wastewater By Electro-Fenton Process

As an industrial power in textile printing and dyeing,a large amount of dye wastewater is discharged in China.At present,the treatment of dye wastewater has attracted widespread attention.In this study,the core-shell nano zero valent Iron and Manganese（nZVIM）was developed,and applied in the treatment of MB-containing wastewater by heterogeneous electro-Fenton process.Firstly,the suitable preparation conditions of nZVIM was determinded.Some properties of nZVIM prepared with the suitable preparation conditions were characterized.Subsequently,the removal efficiencies of heterogeneous electro-Fenton process with nZVIM（nZVIM/EF）were measured at different operation parameters,and the influence of operation parameters on the MB removal in nZVIM/EF process was explored.Meanwhile,the kinetics of MB removal at different operation parameters were analyzed,and the influence degrees of operation parameters were confirmed.Furthurmore,the MB mineralization and current efficiency in nZVIM/EF process were determinded through analyzing the change of TOC in nZVIM/EF process.Moreover,the catalytic performance of nZVIM and the kinds of free radicals in nZVIM/EF process were determinded through the process comparison experiment and quench experiment,respectively.Finally,the generation mechanism of·OH and the degradation pathways of MB in nZVIM/EF process were proposed.The main conclusions of the study are as follows:（1）The preparation temperature and aging time had no significant influence on the MB removal efficiencies of nZVIM in nZVIM/EF process（P>0.05）.For the preparation of nZVIM,the suitable preparation concentrations of Mn²⁺and Fe²⁺was 1.44 g/L and 0.48 g/L,respectively,and the suitable ratio of Mn mass was 75%.The results of scanning electron microscope（SEM）,transmission electron microscopy（TEM）and energy dispersive X-ray spectroscopy（EDX）indicated that nZVIM was a core-shell structure with Fe/Mn core surrounded by Fe/Mn oxide shell.The results of X-ray diffractometer（XRD）and X-ray photoelectron spectroscopy（XPS）showed that the oxide layer of nZVIM was mainly composed of Fe₂O₃,Fe₃O₄,Mn₂O₃ and Mn Fe₂O₄.The saturation magnetization（Ms）value of nZVIM was 16.14 emu/g,which proved that nZVIM has magnetic recovery potential.（2）The removal efficiencies of MB increased firstly and then decreased with the increase of nZVIM dosage.The excessive nZVIM dosage（>50 mg/L）negatively affected MB removal efficiency.The nZVIM/EF process can adapt to a wide range of the initial pH（from 2.5 to 8）with high MB removal efficiencies（from 96.75%to 81.97%）.The higher the applied current in nZVIM/EF process,the better the removal effect of pollutants.However,the excessive applied current（>45 m A）can cause a loss of current efficiency.nZVIM/EF process has a strong adaptability to MB wastewater with a concentration in the range of 0-200 mg/L.Overall,25 mg/L of nZVIM dosage,2.5 of initial pH,45 m A of applied current can be used as the suitable operating parameters in nZVIM/EF process for MB wastewater treatment with a concentration in the range of 0-200 mg/L.（3）The MB removal processes at 300 mg/L of MB initial concentration,and 6 or 8 of initial pH in nZVIM/EF prcess followed the pseudo-second order kinetic model.At other operating parameters,the MB removal processes followed the pseudo-first order kinetic model.The initial pH had the maximum influence degree on the MB removal in nZVIM/EF process,followed by applied current,MB initial concentration,and nZVIM dosage.For the MB mineralization,the considerable MB mineralization（62.3%within 150min and 71.2%within 300min）were gained,indicating that nZVIM was an excellent electro-Fenton catalyst for degradation of MB wastewater.（4）nZVIM had a desirable catalytic property.The electrochemical oxidation（EF oxidation and anodic oxidation）was the main mechanism for the MB removal in nZVIM/EF process.The quench experiment proved that·OH was the main free radical in the nZVIM/EF process for the MB removal.The ways of·OH formation in nZVIM/EF process included Fe heterogeneous catalysis,Mn heterogeneous catalysis and anodic oxidation.Eleven intermediate products were detected in the degradation process of MB by GC-MS.With the oxidation of·OH,these intermediate products eventually decomposed into CO₂,H₂O,NO₃^-,and SO₄^2-.