Preparation And Adsorption Properties Of Magnetic Moringa Oleifera Seed Shell Biochar

With the continuous development and application of the functional components of Moringa oleifera seeds,the waste of Moringa oleifera seed shell（M.oleifera seed shell）is becoming more and more serious.Studying the application potential of M.oleifera seed shells and using discarded resources scientificly and rationally can not only save resources,improve the environment,and realize the reuse value of the waste,but also conform to the current waste-to-rich and recycling model.The model has certain practical significance for building an environment-friendly and resource-saving society.The surface of M.oleifera seed shell is rough and porous.These characteristics make M.oleifera seed shell a promising source of green and efficient biochar materials.Based on this,the goals of research as following:firstly,establish a method for preparing magnetic moringa seed shells biochar（Fe₃O₄-MOS）by using Moringa oleifera seeds shell as raw material,K₂CO₃as impregnation-pyrolysis activator and Fe₃O₄as support under ultrasound assisted conditions.Secondly,the characterization of the composition,structure and physicochemical properties of Fe₃O₄-MOS wre described by N₂adsorption and desorption,SEM-EDS,XPS,XRD,and FTIR.Thirdly,the adsorption and removal performance and mechanism of magnetic seed shell biochar on methylene blue in aqueous solution and free fatty acids（FFA）in vegetable oil were mainly studied.It provides a theoretical basis for the practical application of magnetic Moringa oleifera seed shell biochar and a new idea for the comprehensive utilization of Moringa oleifera seed shell.The main research contents and results are as follows:1.Under ultrasonic assisted conditions,magnetic moringa seed shells biochar（Fe₃O₄-MOS）as prepared from M.oleifera seed shell and using co-impregnation-pyrolysis of K₂CO₃and Fe₃O₄.The physicochemical properties of Fe₃O₄-MOS were characterized through N₂-adsorption and desorption,XRD,SEM-EDS,FTIR,XPS and other characterization techniques.The results of N₂-adsorption and desorption showed that the surface area,pore volume and pore diameter of the Fe₃O₄-MOS were17.90 cm²/g,0.075 cm³/g and 4.443 nm,respectively.The XRD,XPS and FTIR results showed that there were diffraction peaks of Fe crystals on the surface of the prepared Fe₃O₄-MOS,which proved that Fe₃O₄was successfully loaded on the surface of the biochar,and its connection mode with the biochar may be Fe-O-C and Fe-O-C;The SEM-EDS results showed that the Fe₃O₄-MOS had a large number of fine pore structures.Compared with that of unmagnetized biochar,the appearance of the magnetic seed shell biochar has changed significantly And crystals of different agglomeration degrees were attached to the surface of the material and filled in the formed pores.The crystals on the surface contain 48.71%of carbon,9.24%of ions,11.71%of oxygen and other substances.It indicated that Fe₃O₄was successfully loaded on the magnetic Moringa seed shell biochar.2.Using the obtained biochars as adsorbent and methylene blue（MB）as the adsorption object,to investigate the influence of different reaction temperature,time,initial p H of the solution,dosage,and initial mass concentration on adsorption of MB.In addition,kinetics,thermodynamics and isotherm adsorption models were appled to study the adsorption mechanism of MB.The study found that under the conditions of the adsorption temperature was 40℃,the dosage was 0.02mg/g,the initial mass concentration was less than 60 mg/L,and the p H was 7,the adsorption efficiency of MB was close to 100%.The fitting results of kinetics,thermodynamics,and isotherm adsorption model showed that the adsorption of MB by Fe₃O₄-MOS is a spontaneous and endothermic process,and chemical adsorption is the main rate-limiting process accompanied with physical adsorption and internal diffusion.Moreover,the distribution of MB on the surface of activated carbon is not uniform in a single layer but multilayer adsorption occurs on a heterogeneous solid surface.After five adsorpton-desorption cycles,the prepared material still maintains strong adsorption performance for MB.3.Fe₃O₄-MOS was used as a deacidification agent to remove FFA from rapeseed oil.The effect of deacidification temperature,time,stirring rate,initial acid value and addition amount on the deacidification process were studied.Thermodynamics,kinetics and isothermal adsorption models were used to reveal the mechanism of Fe₃O₄-MOS of removing FFA,and further verify the feasibility of the prepared materials to adsorb free fatty acids（FFA）.The results showed that the deacidification rate of rapeseed oil could reach 80%when the stirring rate was 200 r/min,the initial acid value was 9.46 mg/g,and the deacidification temperature was 70℃for130 min.The fitting results of kinetics,thermodynamics,and isotherm adsorption model showed that the adsorption of FFA by Fe₃O₄-MOS is a spontaneous and endothermic process,and chemical adsorption is the main rate-limiting process accompanied with physical adsorption.The kinetic fitting results showed that the chemical adsorption was the main rate-limiting process in the adsorption and removal of FFA,accompanied by physical adsorption.The thermodynamic fitting results showed that the adsorption and removal of FFA by magnetic seed-shell biochar was spontaneous,endothermic and entropy increased.The fitting results of the isothermal adsorption model showed that the Fredunlich isothermal adsorption model could well fit the adsorption process of FFA removal by magnetic seed shell biochar.