Study On Preparation Of Magnetic Adsorption Materials And Adsorption Properties For Hexavalent Chromium Ions

With the rapid development of modern industry,a large amount of carcinogenic,highly toxic Cr?VI?-containing wastewater is discharged into natural water bodies,causing a great harm to humans and the environment.Magnetic composites have become one of the most studied adsorption materials at home and abroad due to their unique paramagnetic properties,high adsorption capacity,and easy recycling.However,such adsorption materials generally have the disadvantages of difficult solid-liquid separation,weak acid resistance of magnetic core,inadequate range of applicable pH,low adsorption capacity,and lack of mechanism research.To adress these problems mentioned above,Fe₃O₄ nano-magnetic particle was used as the magnetic core,and different materials were used to build a magnetic composite adsorption material in this article.The preparation conditions of the material was optimized,the material was characterized,and the adsorbent was applied to the treatment of Cr?VI?wastewater.The influencing factors and adsorption mechanism of its adsorption performance were investigated.The main research contents are as follows:The superparamagnetic micro-nano-bio-adsorbent PDA/Fe₃O₄/BC was prepared by solvothermal and in-situ polymerization method.The best preparation conditions were obtained by investigation:the pyrolysis temperature of biochar?BC?was 600?,the molar concentration of FeCl₃ was 0.05 mol·L^-1,and dopamine?DA?concentration was 2 g·L^-1,and it was used for adsorption of Cr?VI?-containing wastewater.The specific surface area and magnetization of the adsorbent were increased by the modification of polydopamine?PDA?and Fe₃O₄,and the surface functional groups were also changed,resulting in PDA/Fe₃O₄/BC had good adsorption performance and reusability.The optimal conditions for Cr?VI?wastewater adsorption:initial pH was2.0,adsorption equilibrium time was 360 minutes,and initial Cr?VI?concentration was 50 ppm.The adsorption process was complied with the pseudo-second-order kinetic model and the Langmuir isothermal model,and it was an entropy driven spontaneous endothermic process.The maximum adsorption capacity was 23.89mg·g^-1,the removal rate was 99.37%.Asurfactant-functionalizedmagneticMOF@MOFadsorbent?Fe₃O₄@UiO-66@UiO-67/CTAB?was prepared by solvothermal method,and the optimal preparation conditions were investigated:the molar concentration of UiO-66and UiO-67 were 0.3 mM,and the ratio of the molar concentration of UiO-66/UiO-67was 1/1,and it was used for the adsorption of Cr?VI?-containing wastewater.The adsorption performance of MOF@MOF adsorbent for Cr?VI?was better than that of a single MOF?UiO-66 or UiO-67?adsorbent.The optimal conditions for Cr?VI?wastewater adsorption:initial pH was 2.0,adsorption equilibrium time was 240minutes,and initial Cr?VI?concentration was 50 ppm.Fe₃O₄@UiO-66@UiO-67/CTAB showed excellent adsorption capacity and reusability.Its maximum adsorption capacity was 932.10 mg·g^-1 and the removal rate was 99.56%.The adsorption process was conformed to the pseudo-second-order kinetic model and Langmuir isotherm model,and it was an entropy-driven spontaneous endothermic process.The mechanism study showed that the excellent adsorption efficiency of Fe₃O₄@UiO-66@UiO-67/CTAB was attributed to the electrostatic adsorption and reduction of Cr?VI?.A magnetic core-shell composite?Fe₃O₄@UiO-66@PANI?was synthesized by a solvothermal chemical oxidation method,and the optimal preparation conditions were investigated:the molar concentration of UiO-66 was 0.3 mM,and the volume ratio of acetic acid:hydrochloric acid was 0.3:0.3,the concentration of aniline?Ani?is 0.2mol·L^-1,and it was used for adsorption of Cr?VI?-containing wastewater.Fe₃O₄@UiO-66@PANI showed excellent Cr?VI?removal rate,regeneration and reusability due to the porosity and stability of UiO-66 and the stability of polyaniline?PANI?,high acid resistance and multiple reactive groups?reduction and chelation?.The optimal conditions for Cr?VI?wastewater adsorption:initial pH was 2.0,adsorption equilibrium time was 120 minutes,and initial Cr?VI?concentration was 50ppm.The adsorption process was conformed to the pseudo-second-order kinetic model and Langmuir isothermal model,and it was an entropy-driven spontaneous endothermic process.Its maximum adsorption capacity was 448.01 mg·g^-1 and the removal rate was 99.90%.The mechanism study showed that the excellent adsorption and removal performance of Fe₃O₄@UiO-66@PANI due to the electrostatic adsorption and reduction of Cr?VI?and the chelation of Cr³⁺.In this article,Fe₃O₄ nano-magnetic particle was used as magnetic core,porous materials such as biochar and metal organic framework were used as shell,and PDA,CTAB and PANI were further used as functionalizing agents.The three different types of adsorbents PDA/Fe₃O₄/BC,Fe₃O₄@UiO-66@UiO-67/CTAB and Fe₃O₄@UiO-66@PANI were constructed by solvothermal and in-situ polymerization an the maximum adsorption capacities of Cr?VI?were 23.89,932.10 and 448.01mg·g^-1,respectively.The adsorption capacity of Fe₃O₄@UiO-66@UiO-67/CTAB was higher than that of most of the magnetic composite adsorbents reported.The research work and results in this paper provide new ideas and data references for the preparation of magnetic composite adsorbents.