Study On The Preparation Of Ferric Manganese Composites And Its Adsorption As Well As Catalytic Properties

With the rapid development of industry and agriculture,a large amount of heavy metals and pharmaceutical wastewater have been produced.These wastewater once discharge into the environment without treatment,they would result in critical health problem to the life of animal and plant,even human beings.Owing to the excellent physical and chemical properties of spinel manganese ferrate（MnFe₂O₄）,it can be used as catalytic,magnetic and gas sensitive material.In this study,two magnetic adsorbent which was well-targeted to heavy metals have been synthesized via dipping method and hydrothermal co-precipitation method by loading the spinel manganese ferrate onto the surface of materials with larger specific surface area.Furthermore,their adsorption behavior and mechanism have been investigated.One of the magnetic adsorbent referred to that the silica was decorated with spinel manganese ferrate and chitosan（MnFe₂O₄@CS-SiO₂）,was applied to deal with the pharmaceutical wastewater which characterized with high content of organic matter and complex composition by catalyzing sodium persulfate for producing sulfate radical（SO₄^-·）.The primary research contents of this paper are as following:（1）With the mole ratio 2:1 of M(Fe³⁺):M(Mn²⁺),the magnetic MnFe₂O₄ was synthesized via hydrothermal co-precipitation method.The morphology and structure of MnFe₂O₄ have been characterized with the methods of Scanning electron microscope（SEM）,Fourier transform infrared spectroscopy（FTIR）,Brunauer-Emmett Teller（BET）,X-ray diffraction（XRD）.The results indicated that the nano-magnetic adsorbents MnFe₂O₄ have been successfully synthesized,and they are approximately spherical-like in shape,with a specific surface area of 75.70 m²/g and a particle size of 20-30 nm.It was found that the effect was not satisfactory on the removal of Cu²⁺and Zn²⁺from simulated wastewater through batch experiments.Under the optimal operating conditions,neither the removal efficiency nor the adsorption capacity reached their desired value.（2）According to the mass ratio 1:6 of M（MnFe₂O₄）:M（Al₂O₃）,the MnFe₂O₄ were loaded on the surface of Al₂O₃ to synthesize magnetic adsorbent MnFe₂O₄@Al₂O₃ via the dipping method.The removal efficiency and adsorption capacity of Cu²⁺onto the MnFe₂O₄@Al₂O₃ achieved its maximum at the conditions of 20 mg/L Cu²⁺initial concentration,0.20 g adsorbent dosage,pH 4,and 4 h reaction time,98.3%and 9.78mg/g,respectively.The adsorption mechanism has been characterized with adsorption isotherm,adsorption kinetic,Vibrating sample magnetometer（VSM）,X-ray photoelectron spectroscopy（XPS）,SEM,FTIR,XRD,and BET.The results implied that the adsorption of Cu²⁺onto the MnFe₂O₄@Al₂O₃ may be a multilayer chemisorption process,in which the electrostatic gravitational action provided by the M-OH group may predominate in this adsorption.However,due to the formation of MnFe₂O₄@Al₂O₃ by the dipping method as well as alumina with amphoteric characteristics,they resulted in the low crystallinity of MnFe₂O₄@Al₂O₃ and limited its application in a wide range of pH value.（3）In order to prepare a magnetic adsorbent with wide range of pH value based on the cores of magnetic MnFe₂O₄,a novel magnetic adsorbent coating the chitosan and MnFe₂O₄ onto the silica（MnFe₂O₄@CS-SiO₂）has been successfully synthesized via hydrothermal co-precipitation method,and it was used to treat the simulated wastewater containing Zn²⁺and methylene blue（MB）.The experimental results indicated that the removal efficiencies and adsorption capacities of Zn²⁺and MB reached 63.3%and 98.12%,31.65 mg/g and 49.06 mg/g respectively under 100 mg/L initial adsorbate concentration,0.20 g adsorbent dosage,pH 7,and 4 h reaction time.The adsorption mechanism has been characterized with adsorption isotherm,adsorption kinetic,Scanning electron microscope and energy spectrum（SEM-EDS）,VSM,FTIR,XRD,XPS,and BET.The removal of Zn²⁺may contribute to the diverse functional groups provided by CS,while the MB removal may ascribe to the large specific surface area of MnFe₂O₄@CS-SiO₂.The magnetic adsorbent of MnFe₂O₄@CS-SiO₂ was confirmed to be an environmental friendly adsorbent due to its good reusability after five consecutive cycles.（4）To verify that the metal oxide composite adsorbents may also be excellent catalysts,MnFe₂O₄@CS-SiO₂ was applied to deal with the pharmaceutical wastewater by catalyzing sodium peroxydisulfate for producing SO₄^-·.The parameters,such as chemical oxygen demand（COD）,ammonia nitrogen,and color have been investigated.Combining the results concluded from the samples before and after treatment of three-dimensional fluorescence excitation-emission spectrum（3DEEMs）and FTIR,the advanced oxidation processes（AOPs）which used MnFe₂O₄@CS-SiO₂as catalyst has great efficiency on the degradation of pesticide wastewater.The characteristics of raw wastewater are as following:COD 12,000-14,000 mg/L,ammonia nitrogen 5,000 mg/L,and color 1,000 times.After approximately 9 h treatment,the removal efficiencies of COD,ammonia nitrogen,and color reached53.62%,81.77%,and 90%,respectively.The removal of these parameters can be ascribed to the macromolecular organic matters in the samples were oxidized into micro-molecular organics matters even mineralized into CO₂ and H₂O directly according to characterizations of samples before and after treatment.