Preparation Of Novel Magnetic Adsorbents And Their Adsorption Behavior For Heavy Metal Ions

Heavy metal pollution not only causes damage to the ecological environment,but also threatens human health through the bioaccumulation of the food chain.Therefore,how to effectively treat heavy metal wastewater pollution has attracted widespread attention from society.The adsorption is considered to be one of the ideal heavy metal wastewater treatment technologies because of simple operation,stable removal effect and reusability of adsorbents.In this article,new core-shell structure magnetic adsorbents were prepared by supramolecular self-assembly of lysozyme for the adsorption of heavy metal ions from aqueous solution.The main research works are as follows:Fe₃O₄ nanoparticles were synthesized by co-precipitation method,and magnetic silica Fe₃O₄@SiO₂ was prepared by modified sol-gel method.A novel amyloid phase-transited lysozyme film-coated magnetic silica nano-adsorbent Fe₃O₄@SiO₂@PTL was prepared by supramolecular self-assembly of lysozyme.Thiol functional group was introduced on the surface of Fe₃O₄@SiO₂@PTL through esterification reaction to obtain thiol-modified amyloid phase-transited lysozyme nano-adsorbent Fe₃O₄@SiO₂@PTL-SH.Meanwhile,SEM,TEM,AFM,FT-IR,XPS,XRD,VSM,TG and BET techniques were used to to characterize the physical and chemical structure of Fe₃O₄@SiO₂@PTL and Fe₃O₄@SiO₂@PTL-SH,and the results showed that both adsorbents were core-shell structure with a double-layer film.In addition,the surface of Fe₃O₄@SiO₂@PTL contained active groups such as hydroxyl,carboxyl,amino,amide and thiol,which could provide multiple adsorption sites for heavy metal ions.After modification,the content of thiol groups on the surface of Fe₃O₄@SiO₂@PTL-SH increased,which improved adsorption capacity of Hg²⁺significantly.Fe₃O₄@SiO₂@PTL was used to remove Hg²⁺,Cd²⁺,Pb²⁺,Cu²⁺,Ni²⁺,Co²⁺and Mn²⁺in wastewaters,and single-component and mixed-component experiments showed that the adsorbent exhibited a good adsorption capacity and selectivity for Hg²⁺,and modified Fe₃O₄@SiO₂@PTL-SH also had a superior uptake performance toward Hg²⁺.Therefore,in this study,the adsorption behavior of Fe₃O₄@SiO₂@PTL and Fe₃O₄@SiO₂@PTL-SH were investigated in depth with Hg²⁺as the target pollutant.The results showed that the adsorption equilibrium of both two adsorbents was reached expeditiously within 5 minutes,and the process of adsorption followed pseudo-second-order kinetic model.Langmuir model could fit the adsorption isotherm data of the two materials well,and adsorption were spontaneous endothermic reaction.Coexisting cations include Na⁺、K⁺、Ca²⁺and Mg²⁺had a slight adverse effect on adsorption of Hg²⁺.Moreover,the high concentration of Cl^-had a significant inhibitory effect on the adsorption performance of Fe₃O₄@SiO₂@PTL among all coexisting anions,and Fe₃O₄@SiO₂@PTL-SH had better adsorption selectivity for Hg²⁺than Fe₃O₄@SiO₂@PTL.In addition,thiourea and hydrochloric acid mixture could achieve good desorption of the adsorbents,and the adsorption capacity of Hg²⁺would not decrease significantly after 5 adsorption-desorption cycles.The Guassian simulation calculation,FT-IR and XPS implied that the main adsorption mechanisms of the two adsorbents were electrostatic attraction and coordination complexation,and coordination contributed more in the adsorption process of Fe₃O₄@SiO₂@PTL-SH.