Preparation Of Core-shell Structure Composite Materials And Their Adsorption Performance Towards Heavy Metal Ions

Cr（VI）is extremely toxic to organisms,the pollution problem caused by Cr（VI）is becoming more and more serious with the increase of industrial activities.Due to its unique physical and chemical properties,the core-shell structure materials have attracted much attention in the adsorption of heavy metals in wastewater.In this paper,three kinds of core-shell structure heavy metal adsorption materials with excellent properties were prepared from the new preparation methods,hollow core-shell structure design and practical applications.The main findings are as follows:（1）Three kinds of core-shell structure adsorbents（Fe₃O₄@SiO₂-1N,Fe₃O₄@SiO₂-2N,Fe₃O₄@SiO₂-3N）modified by silane coupling agents with different N contents were synthesized by simple co-condensation method.XRD,SEM,FT-IR,N₂adsorption-desorption,and elemental analysis were used to compare the differences in morphology,surface functional groups,and N densities when using different N number of silane coupling agents as modifiers.The experimental results of the adsorption kinetics show that the equilibrium can be reached after 60 min adsorption.With the increase of N contents,the maximum adsorption of each adsorbent shows the trend of Fe₃O₄@SiO₂-1N（79.74 mg/g）>Fe₃O₄@SiO₂-2N（63.05 mg/g）>Fe₃O₄@SiO₂-3N（55.37 mg/g）.The results of Zeta potential and elemental analysis indicate that the modified adsorbent shows a large change in the amount of charged and N-containing density.The main effect of the modified adsorbent on Cr（VI）is electrostatic interaction.Due to the presence of steric hindrance effects,the adsorbent surface is too detrimental to adsorption when its density of active sites is too high.（2）Hollow core-shell structure adsorbent F-C@SiO₂ was synthesized by adopting hollow carbon sphere as core,SiO₂ as shell layer,and CTAB as modifier.The results of Cr（VI）adsorption experiments show that the existence of cavity structure makes the adsorption performance of F-C@SiO₂ significantly better than that of C and SiO₂.The modification of CTAB further improves the adsorption performance,making the adsorption capacity reach 202.02 mg/g.Coexistence anion interference experiments showed that the effect of anion on the adsorption showed a trend of HPO₄^2->SO₄^2->NO₃^->Cl^-.When coexisted with the mixed cation Cu（II）,Ni（II）,Zn（II）,and Cd（II）,F-C@SiO₂ exhibits good selectivity for Cr（VI）.After five times of cyclic adsorption experiments,the adsorption capacity of F-C@SiO₂ can reach 74.82%for the first time.The adsorption mechanism studies using FT-IR and XPS show that the adsorption process not only has an electrostatic attract but also undergoes the reduction and adsorption of Cr（VI）by the electron donor of the adsorbent.（3）The amino-modified magnetic carbon material with irregular core-shell structure was prepared by one-pot hydrothermal method.The resulting material had the highest saturated adsorption capacity when glucose was used as the carbon source.The maximum adsorption capacity of MP-N was 205.94 mg/g.Simulated mixed cation experiments show that MP-N has good selectivity to Cr（VI）,and the adsorption capacity can still reach more than 90%for the first time after 5 cycles of adsorption.When the concentration of adsorbent is 7 g/L,the removal rate of Cr（VI）in actual wastewater（Cr（VI）content of 417.15 mg/L）is over 99%.It can be seen from the breakthrough curve that the MP-N adsorption column can still maintain the Cr（VI）content in the effluent up to the national emission standards 0.5 mg/Lwhen adsorbed under dynamic conditions for 42 h.Therefore,the amino-functionalized magnetic carbon material in this paper has practical application value for the treatment of Cr（VI）containing wastewater.