The Synthesis And Cr(?) Removal Of Magnetic Fe-based Core/Shell Microspheres

Recently,pollution of Cr???has been one aspect of the broader topic of environmental issues,particularly for water environment,because of effluent toxicity.Up to now,adsorption based on organics as adsorbents is used as a common method to remove Cr???.However,the adsorpted Cr???may easily transported to a surface of adsorbents where there is a repollution on the corresponding surface.Another useful method is defined into chemical reduction,in which the Cr???can be reduced to nontoxicity Cr?III?and deposited whithout such repollution mentioned above.As for a ferromagnetic nanomaterial,single elemental Fe possesses many advantages of removing toxicity Cr???over other nanomaterials,such as strong magnetism,high reduction,and environmental friendliness.However,an effect of remove productivity will be largely decreased owing to the low magnetism and reduction which is resulted from the high surface free energy of Fe⁰.Lower reactivity caused by the gather of Fe⁰ with each other can be attributed to gravity,magnetic force and Van der Waals'force,which results in a limited application of Fe⁰.There are two methods employed to solve the problem mentioned above.Firstly,because of the low cost and good resistance to corrosion of Ni,core/shell Fe@Ni microspheres are synthesized by coating Fe⁰with Ni as the catalytic metal.During the reaction process,the generated H·can rapidly reduce Cr???for removal purposes.Secondly,because of the strong adsorption ability of Fe₂O₃ to Cr???,the Fe@Fe₂O₃microspheres are synthesized using Fe₂O₃ as modifier and then remove the Cr???by the dual function of adsorption and reduction.To sum up,in this article,we report the synthesis,saturation magnetization,Cr???remove ability and related mechanism of core/shell Fe@Ni microspheres and Fe@Fe₂O₃microspheres.Specific research contents are as follow:?1?Synthesis of core/shell Fe@Ni microspheres and their magnetic and Cr???removalThe core/shell Fe@Ni microparticles are synthesized by chemical vapor deposition method.The samples are confirmed to a core/shell structure with the diameter of 400 nm and shell thickness of 70 nm The as-fabricated core/shell Fe@Ni microparticles are shown that the saturation magnetization is up to132.8 emu/g by magnetic hysteresis loops.And the high saturation magnetization is beneficial to fast magnetic separation.The removal rate of the Fe@Ni microspheres and Fe⁰ is 81%and 70%,respectively,which illustrates the removal rate is improved by using Ni as catalytic metal.The removal amount of Fe@Ni microspheres is calculated to be about 81 mg/g.?2?Synthesis of core/shell Fe@Fe₂O₃ microspheres and their magnetic and Cr???removalThe core/shell Fe@Fe₂O₃ microspheres are synthesized by using NaBH₄ to reduce FeCl₃·6H₂O under ultrasonic aid.The samples have well monodispersity,large specific surface area,the diameter of 100 nm and shell thickness of 5 nm.The core/shell Fe@Fe₂O₃ microspheres are shown that the saturation magnetization is up to 83.6 emu/g by magnetic hysteresis loops.And the high saturation magnetization is beneficial to fast magnetic separation.We subsequently studied the effects of molecular oxygen on the removal of Cr???with core/shell Fe@Fe₂O₃ microspheres by measuring the production of ferrous ion,total dissolved iron,Cr???and Cr?III?in aqueous solution.It is found that Cr???is removed by core/shell Fe@Fe₂O₃ microspheres via adsorption and reduction under anoxic and oxic conditions.The reduction of Cr???by Fe²⁺mainly is accounted for the removal of Cr???and the removal rate is up to 98%under Ar conditions.The inhibitory effect of molecular oxygen on the Cr???removal is attributed to the adverse roles of reactive oxygen species generated during the removal of Cr???with core/shell Fe@Fe₂O₃microspheres.