Preparation And Properties Of Magnetic Nano Fe₃O₄/MWSC Catalyst

In recent years,about 15%of dyes have been discharged into the aquatic environment from textile and printing industries.Due to the ineffective treatment of these dyes,serious water pollution has been caused,which poses a great threat to the ecosystem and human health.The release of dye wastewater is It is an important source of aesthetic pollution and eutrophication in the water ecological environment.Dye wastewater has the characteristics of large amount of organic matter,complex composition,deep chroma,strong biological toxicity,refractory degradation,and high concentration of COD and BOD₅.Therefore,it is necessary to seek a new technology with high efficiency,low cost and environmental protection for advanced treatment of industrial dye wastewater.In this research paper,a novel high-adsorption walnut shell biochar material rich in phenolic hydroxyl and other oxygen-containing functional groups was obtained by changing the conditions of pyrolysis;on this basis,the walnut shell biochar was activated by KOH high temperature activation method,to obtain activated walnut shell biochar;then the activated walnut shell biochar was modified by impregnation method with cerium nitrate solution and roasted to obtain cerium modified walnut shell carbon;finally,magnetic nano-Fe₃O₄/MWSC composite catalyst was obtained by one-step co-precipitation method As a Fenton-like composite material.The pore structure,composition,microscopic morphology and oxidation catalytic activity of the magnetic nano-Fe₃O₄/MWSC composite catalyst were analyzed by various characterization methods,and the construction of an efficient Fenton-like reaction catalytic system was realized.The adsorption and degradation process of the typical cationic dye methylene blue in this Fenton catalytic system was further explored,and the main factors in the catalytic degradation process and the stability of the catalyst were discussed.The main conclusions are as follows:The optimum preparation conditions for the preparation of walnut shell biochar by high temperature pyrolysis were as follows:the heating rate was 10℃/min,the final temperature of pyrolysis was 800℃,and the holding time was 2 h.The specific surface area of the best biochar was 353.4 m²/g,and its maximum adsorption capacity for methylene blue was 128 mg/g.By BET,SEM,XRD,FTIR and XPS,it was found that the surface of walnut shell carbon was smooth and the carbon skeleton was complete.And it is not easy to collapse,the overall structure is flaky or layered,the pore structure is developed,mainly coarse micropores,the pore system is continuous and complete,rich in oxygen-containing functional groups,producing a small amount of graphite crystallites,and has good adsorption performance and load.Function.Cerium-modified walnut shell carbon was prepared by impregnation method,and characterized by BET,SEM,XRD,FTIR and XPS:Ce O₂ particles were successfully loaded and uniformly loaded on the surface of walnut shell carbon,which made the surface area and total surface area of walnut shell carbon.The pore volume is significantly increased;the adsorption performance of the modified walnut shell carbon material impregnated in 0.01mol/L cerium nitrate solution is better than that of the modified walnut shell carbon material impregnated with 0.02 mol/L cerium nitrate,and has a relatively good adsorption performance.regeneration ability.The adsorption study showed that in the adsorption system of 298.15 K,p H=7,c=500 mgL^-1,6 h,the adsorption capacity of cerium modified walnut shell carbon on methylene blue reached339.84 mgg^-1;the cerium walnut shell carbon sample The adsorption of methylene blue conforms to the pseudo-second-order kinetic model,and its adsorption is the rate-controlling step of the adsorption process by chemical adsorption interacting with various mechanisms.The Langmuir and Freundlich models are used to fit the isotherm adsorption curve,and it is found that it is more in line with Langmuir model,and its constant k _L is much larger than that of walnut shell carbon,indicating that the cerium modification can significantly improve the adsorption effect of cerium modified walnut shell carbon.Nano-Fe₃O₄/MWSC catalysts were successfully prepared by one-step co-precipitation method,and the magnetic nano-Fe₃O₄ particles with face-centered cubic crystal structure were successfully supported on the nano-Fe₃O₄/MWSC imitation enzyme catalysts by BET,SEM,FTIR,XRD,XPS and other characterizations.The Fe element exists in the form of Fe³⁺and Fe²⁺,and is uniformly loaded on the surface of the MWSC in the form of chemical bonding,which significantly reduces the surface area and the total pore volume of the MWSC;the optimal loading condition of the magnetic nano Fe₃O₄ particles is:the total iron salt concentration is 0.0325 mol/L,Fe³⁺:Fe²⁺=1.75:1,the reaction p H is 10,and the reaction temperature is 70℃.At this time,the nano-Fe₃O₄/MWSC imitation enzyme catalyst has the best degradation and removal rate of methylene blue.The saturation magnetization of the nano-Fe₃O₄/MWSC imitated enzyme catalyst is 32.33 emu/g.This material has good magnetic responsiveness and can be easily and efficiently separated and recovered.Taking methylene blue as the research object,the adsorption performance and mechanism of the nano-Fe₃O₄/MWSC catalyst were studied.The results showed that the adsorption of methylene blue by the magnetic nano-Fe₃O₄/MWSC composite catalyst conformed to the pseudo-second-order kinetic model,indicating that the chemical interaction with multiple mechanisms Adsorption is the rate-controlling step of the adsorption process,which is more in line with the Langmuir model,and the adsorption process is affected by many factors.When the initial concentration of methylene blue was 120 mg/L,the p H was 7,and the temperature was 25°C,the saturated adsorption capacity was 108.20 mg/g.It shows that the catalyst has good affinity for methylene blue.Finally,taking methylene blue simulated printing and dyeing wastewater as the degradation object,the catalytic performance of the nano-Fe₃O₄/MWSC composite catalyst was studied,and the main factors affecting the degradation process and its reusability were tested.The optimal conditions were:initial p H was 3.0,initial H₂O₂concentration was 30 mmol/L,the dosage of nano-Fe₃O₄/MWSC catalyst was 1.0g/L,and the temperature was 25℃.Under these conditions,the removal rate of methylene blue was 93.25%within 120 min.The nano-Fe₃O₄/MWSC composite catalyst was reused 4 times,and the methylene blue removal rate was between 87.1%and 91.5%,which could be reused well.Among them,the dissolution amount of Fe is between1.815 mg/L and 3.69 mg/L,and the dissolution amount is relatively low.It is a magnetic water treatment catalyst with stable catalytic degradation performance and long-term repeated use.