Preparation And Characterization Of Magnetic Manganese Cobalt Ferrite Nanomaterials And Their Applications In Pollutant Removal

As society continues to progress,the treatment of environmental pollutants is being handled more.Among these,the heavy metal mercury and dye pollutions are particularly problematic.Mercury is persistent,bioaccumulative,highly toxic,and highly volatile in the environment.Dye wastewater is toxic,mutagenic,carcinogenic,and biodegradable.Both pollutants can pose serious risks to human health and cause serious environmental problems.Existing adsorbents are complicated to prepare and cannot be recycled after adsorption.Therefore,there is an urgent need to develop an adsorbent to remove mercury and dye,and enabling the efficient reuse of environmental resources and preserving human health and safety.As a non-metallic material with a large specific surface area and many active sites,magnetic ferrite nanomaterials can quickly achieve solid-liquid or gas-solid separation under the action of an applied magnetic field and can effectively avoid secondary contamination.It is important to explore low cost,high performance and high utilization adsorbents for elemental mercury and dye removal studies.In this paper,Mn_0.5Co_0.5Fe₂O₄ nanomaterials were prepared by a rapid combustion method based on metal nitrate as raw material and absolute ethanol as solvent,and the nanomaterials were applied to elemental mercury（Hg⁰）and Congo red（CR）removal,respectively.Main outcomes of the research are as follows:（1）Magnetic Mn_0.5Co_0.5Fe₂O₄ nanomaterials for controlled preparationThe magnetic Mn_0.5Co_0.5Fe₂O₄ nanomaterials were prepared by a rapid combustion method in which absolute ethanol as solvent and manganese nitrate,cobalt nitrate,and iron nitrate were employed as solutes.Magnetic Mn_0.5Co_0.5Fe₂O₄ nanomaterials were successfully prepared and presented in particle form according to XRD,VSM,FTIR,XPS,and other characterization methods.The average grain size of the Mn_0.5Co_0.5Fe₂O₄ nanomaterials grew from 19.5 nm to23.3 nm and the saturation magnetization went up from 25.4 emu·g^-1 to 63.6 emu·g^-1 as the volume of ethanol increased from 20 m L to 100 m L during the preparation process.When calcination temperature was increased from 400°C to 700°C,the average grain size grew from19.5 nm to 47.0 nm,while the saturation magnetization went up from 25.4 emu·g^-1 to 76.1emu·g^-1.In order to benefit the application of magnetic nanomaterials,the following conditions were chosen:calcination temperature of 400°C,absolute ethanol volume of 20 m L.The obtained Mn_0.5Co_0.5Fe₂O₄ nanoparticles had a specific surface area of 103.0 m²·g^-1,an average particle size of 26.8 nm,and a saturation magnetization of 25.4 emu·g^-1.（2）Magnetic Mn_0.5Co_0.5Fe₂O₄ nanoparticles for the removal of Hg⁰ from simulated flue gasThe mercury adsorption and regeneration properties of the nanoparticles were investigated using a fixed-bed experimental system.The results showed that the Mn_0.5Co_0.5Fe₂O₄nanoparticles prepared at the calcination temperature of 400°C with absolute ethanol volume of20 m L had the best adsorption performance of Hg⁰.Mn_0.5Co_0.5Fe₂O₄ nanoparticles had the best adsorption capacity of 9.4μg·g^-1 for Hg⁰ at an adsorption temperature of 30°C under a space velocity of 2.4×10⁴ h^-1.When the permeation temperature was increased to 70°C,the adsorption capacity for Hg⁰ reached 560.6μg·g^-1.The Hg-TPD and XPS characterization results indicated that the chemisorbed oxygen(O_ads),Mn³⁺,and Fe³⁺in the adsorbent were involved in the oxidation of Hg⁰ to generate Hg O on the adsorbent surface.After six times of adsorption and desorption,the adsorption capacity of Mn_0.5Co_0.5Fe₂O₄ nanoparticles for Hg⁰ still kept 39.4μg·g^-1,which was 71%of the first adsorption capacity,which indicated that magnetic Mn_0.5Co_0.5Fe₂O₄ nanoparticles were the promising adsorbent for mercury removal.The magnetic reuse assembly was designed based on effective distance tests,magnetic field strength at different locations and magnetic absorption rate of magnetic nanomaterials by magnetic field length to reveal the relationship between magnetic field size,magnetic field spatial distance,magnetic field length and magnetic nanomaterials.A new green treatment technology route for coal-fired power plants that can be recovered and recycled.（3）Magnetic Mn_0.5Co_0.5Fe₂O₄ nanoparticles for the adsorption of CRRemoval of CR from solution was performed with magnetic Mn_0.5Co_0.5Fe₂O₄ nanoparticles.Adsorption kinetic models and isotherm models were applied to analyze the adsorption process of CR onto magnetic Mn_0.5Co_0.5Fe₂O₄ nanoparticles.The experimental data was consistent with Pseudo-second-order kinetic model and Freundlich isotherm model,which demonstrate that the adsorption process was chemisorbed and that it was easy to adsorb.At 303 K,313 K,and 323 K,thermodynamic investigation was applied for analyzing the effect of temperatures on the adsorption capacity of CR onto magnetic Mn_0.5Co_0.5Fe₂O₄ nanoparticles,and the results showed that the adsorption process was a spontaneous exothermic process.At 303 K and the initial CR concentration of 100 mg·L^-1,the ionic strength of Clˉin CR solution had no obvious effect on adsorption efficiency of magnetic Mn_0.5Co_0.5Fe₂O₄ nanoparticles.The maximum adsorption capacity of CR onto magnetic Mn_0.5Co_0.5Fe₂O₄ nanoparticles was 58.3 mg·g^-1 at p H 2.The ion leaching experiment and XRD demonstrated that magnetic Mn_0.5Co_0.5Fe₂O₄ nanoparticles had good stability,and the relative removal rate was 93.85%of the initial value after 7 cycles.Cyclic voltammetry（CV）and electrochemical impedance spectroscopy（EIS）demonstrated that CR was adsorbed onto magnetic Mn_0.5Co_0.5Fe₂O₄ nanoparticles,and the electrical conductivity of magnetic Mn_0.5Co_0.5Fe₂O₄ nanoparticles decreased after the adsorption of CR.Finally,magnetic Mn_0.5Co_0.5Fe₂O₄ nanoparticles had an excellent application prospect in CR adsorption.Magnetic Mn_0.5Co_0.5Fe₂O₄ nanoparticles presents good prospects for dye adsorption applications.