The Superparamagnetic Porous Fe₃O₄ Microspheres: Synthesis,Modification And Their Adsorption Performance Of Heavy Metal Ions

With the rapid development of human society,the problem of heavy metal ions pollution has become increasingly serious.The heavy metal ions are not only toxic to the ecological environment,but also cause harmful effects to humans through food chain transfers due to their high toxicity,persistence,and hard to degrade.Therefore,the removal and treatment of heavy metals ions in water has received widespread attention.At present,the adsorption method is favored by many scientific researchers due to its advantages of low cost,simple operation,high efficiency and energy saving,and recyclability.Traditional adsorbents?such as activated carbon and zeolites?often exhibited low adsorption capacities and low removal rates,but nanomaterials used as absorbents demonstrated effectively contaminants removal capability owing to their large specific surface areas and richable surface-active groups,which attracted researchers'attention greatly.Among them,magnetic nano-adsorbents can realize rapid separation from water after adsorption,and thereby reduce energy consumption,which become the current research hotspot.At present,magnetic adsorption materials have the following problems.On the one hand,porous magnetic particle adsorbents are usually obtained by calcining iron-containing precursors,which have disadvantages that the products have ferromagnetic properties and are easily agglomerated;In addition,the products with a relatively low specific surface area and low adsorption capacity usually obtained by solvothermal method.On the other hand,the magnetic polymer composite adsorbent is usually functional modification on the surface of the magnetic core to form a core-shell structure,which have disadvantages that the products are not porous,limiting its adsorption properties.Therefore,the development of magnetic-based composite adsorbents with porous structure is the key to improve the adsorption performance.In this thesis,our research focused on the efficient removal of Pb²⁺and Cr?VI?ions from water by magnetic-based nano-adsorbents,and aim to develop efficient porous superparamagnetic nanosorbents.Through deep investigating the formation process and mechanism of mesopores in superparamagnetic Fe₃O₄ microspheres,the product structure was optimized to realize improved adsorption performance.At the same time,the as-synthesized porous superparamagnetic Fe₃O₄ microspheres were used as templates,polyrhodanine and polypyrrole were used as surface modifiers to further increase their stability and adsorption performance.The relationships between structural parameters like the specific surface area,pore size and modified shells and adsorption capacity were systematically explored for optimal structure,and two kinds of porous magnetic polymer composite nano-adsorbents?Fe₃O₄-polyrodanine and Fe₃O₄-polypyrrole?with efficient adsorption performance were synthesized primarily.The detailed research results are summarized as follows:?1?Using superparamagnetic Fe₃O₄ microspheres as a template,the self-template etching strategy was developed to synthesize porous Fe₃O₄ microspheres.The results show that the porous structure was realized in the interior of Fe₃O₄ microspheres after the smaller units were preferentially etched,and the specific surface area and pore size can be adjusted by controlling the reaction time,and the highest specific surface area(96 m² g^-1)can be achieved.Through systematically studying the formation process of pores,the size-selective and pore-expanding etching mechanisms were proposed,and the influence of specific surface area and pore size of the as-synthesized samples on the adsorption performance of heavy metal ions was explored.The maximum adsorption capacities towards Pb²⁺and Cr?VI?ions by Fe₃O₄ microspheres were112.8 mg g^-1 and 68.7 mg g^-1,respectively.?2?Using the above-synthesized porous Fe₃O₄ microspheres as a template,the in-situ polymerizations of rhodanine and pyrrole monomers on the surface of the porous Fe₃O₄ microspheres were achieved by adjusting the reaction parameters,and porous Fe₃O₄-polymer composite microspheres were finally synthesized.The experimental results show that the original structure of the porous Fe₃O₄ template can be preserved by regulating reaction parameters.The modified polymer layer not only increased the stability of porous Fe₃O₄ microspheres,but also improved the adsorption performance for their abundant functional groups.The test results show that the maximum adsorption capacity of Pb²⁺ions by porous Fe₃O₄-PRd composite microspheres reached 189 mg g^-1,meanwhile the maximum adsorption capacity of Cr?VI?ions by porous Fe₃O₄-PPy composite microspheres was 199.6 mg g^-1,which were much higher than that of the original porous Fe₃O₄ microspheres.And the adsorption performance of the as-synthesized two kinds of composite microspheres were still above 90%after five cycles of adsorption and desorption,exhibiting excellent recycling ability.