Study On Synthesis And Adsorption Properties Of New Core-shell Magnetic Adsorbent

With the acceleration of industrialization,the problem of water pollution has become more and more serious,especially the ubiquitous organic dyes and heavy metal ions on water pollution.The removal of organic dyes and heavy metal ions in water by adsorption is a commonly used technology.Porous silica has become a widely studied adsorbent material due to its advantages such as large specific surface area,environmental protection,low price,and good stability.However,porous silica adsorbents are difficult to separate and recycle from water.Magnetic nanoparticles Fe₃O₄ can help adsorbents to be quickly recovered from solution by magnetic separation technology because of their superparamagnetic properties.Therefore,adsorbents combining mesoporous silica and magnetic nanoparticles have great application potential.In this paper,the growth-induced corrosion method is used to prepare a smooth and rough surface magnetic adsorbent,and the adsorbent has an egg yolk core-shell structure.This study explored the adsorption effect of magnetic adsorbents on organic dyes and heavy metal ions in water from the aspects of adsorption equilibrium,adsorption kinetics and adsorbent regeneration.This research has important guiding significance for the control of the morphology and structure of magnetic nanoparticles and the application of magnetic adsorbents in sewage treatment.The main research contents are as follows:（1）The apparent morphology and hierarchical structure of magnetic adsorbents are affected by factors such as surfactants,temperature and growth time.When cetyltrimethylammonium bromide（CTAB）is used as the surfactant,the magnetic adsorbent synthesized by the growth-induced corrosion method has a smooth surface.When cetyltrimethylammonium bromide（CTAB）and sodium salicylate（Na Sal）are used as surfactants,and the mass ratio of CTAB to Na Sal is 10:3,the magnetic adsorbent synthesized by the growth-induced corrosion method has a rough surface.By adjusting the temperature and growth time,it was found that when the two surface types of adsorbents were grown at100℃for 24 h,the thickness of the mesoporous shell of the adsorbent and the thickness of the silica protective layer on the Fe₃O₄ surface were relatively moderate.The adsorbent was characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,and N₂ adsorption-desorption.The results show that the magnetic adsorbents with smooth surface and rough surface have egg yolk core-shell hierarchical structure,and the particle size of both types is about 500 nm.The magnetic adsorbent with a rough surface has a larger specific surface area than the magnetic adsorbent with a smooth surface.The pores of the outer shell of the adsorbent belong to a mixed pore structure of micropores and mesopores.（2）The smooth surface magnetic adsorbents（Fe₃O₄@Si O₂@SPMO-Ph and Fe₃O₄@Si O₂@SPMO-SH）containing benzene ring and sulfhydryl group were prepared,and they were successfully applied to the adsorption of organic dyes and heavy metal ions in water.The saturated adsorption capacity of Fe₃O₄@Si O₂@SPMO-Ph for Rhodamine B is 108.62mg·g^-1,and the adsorption equilibrium is reached in 35 minutes.The adsorption process of this adsorbent for organic dyes is more in line with the Langmuir model and the first-order kinetic model,indicating that the adsorption is mainly single-layer physical adsorption.The saturated adsorption capacity of Fe₃O₄@Si O₂@SPMO-SH for copper ions is 203.39 mg·g^-1,and the adsorption equilibrium is reached in 70 minutes.The adsorption process of this adsorbent for heavy metal ions is more in line with the Langmuir model and the second-level kinetic model,indicating that the adsorption is mainly single-layer chemical adsorption.The adsorption capacity of the two adsorbents is greatly affected by the p H value of the solution.The stronger the acidity,the smaller the adsorption capacity.Moreover,these adsorbents can be desorbed in an acidic environment,so as to achieve the purpose of reuse.This type of adsorbent adsorbs other organic dyes and heavy metal ions,and shows excellent adsorption performance,indicating that this type of adsorbent can be well applied to adsorb organic dyes and heavy metal ions.（3）The rough surface magnetic adsorbents（Fe₃O₄@Si O₂@RPMO-Ph,Fe₃O₄@Si O₂@RPMO-SH）containing benzene ring and sulfhydryl groups were synthesized,and their adsorption properties for organic dyes and heavy metal ions in water were studied.The adsorption process of Rhodamine B on Fe₃O₄@Si O₂@RPMO-Ph can be well described by the Langmuir model,and the saturated adsorption capacity of Rhodamine B by fitting is124.52 mg·g^-1.The adsorption kinetics is more in line with the first-order kinetic model,and the adsorption equilibrium can be reached in 15 minutes,indicating that the adsorption is mainly single-layer physical adsorption.The adsorption process of Fe₃O₄@Si O₂@RPMO-SH on copper ions can also be described by the Langmuir model,and the saturated adsorption capacity for copper ions is 218.86 mg·g^-1 by fitting.The adsorption kinetics is more in line with the second-level kinetic model,and the adsorption equilibrium is reached in 50 minutes,indicating that the adsorption is mainly a single-layer chemical adsorption.The adsorption capacity of the two adsorbents is greatly affected by the p H value of the solution.The adsorbent can be desorbed and regenerated in an acidic environment,and still has good adsorption performance after repeated cycles of use.This type of adsorbent has shown higher adsorption capacity in the test of adsorbing other kinds of organic dyes and heavy metal ions,indicating that this type of magnetic adsorbent can be applied to organic dyes and heavy metal ion water treatment.