Studying On Adsorption Effect Of Fe-MOFs On As(?) And Cd(?) In Water

Heavy metal pollution has become one of the serious environental problems.Arsenic and cadmium are known as carcinogens by the world's environmental organizations.People can also lead to skin diseases,renal dysfunction and other diseases if they long-term exposure to low concentrations of arsenic or cadmium-containing environment.Therefore,the removal of As(?)and Cd(?)in water has become a hot topic to scientists.In this paper,MIL-101(Fe)and Fe3O4@MIL-101(Fe)composite MOFs were prepared by solvothermal method.Their nature characteristics were prepared by XRD,FT-IR,SEM,TEM and TG/TGA.Then the two kinds of MOFs prepared above were applied to the adsorption of As(?)and Cd(?)in water.The main contents and results are as follows:(1)The BET specific surface area of the MIL-101(Fe)composites synthesized in this paper is 2736 m2 g'1,the pore size is 2.5 nm,the pore volume is 0.75 cm3 g-1,which is higher than that of some similar adsorbent materials;The thermal stability of the material is high,and MIL-101(Fe)starts to decompose at about 400 ?.Metal Fe has an empty 3d orbit,which is beneficial to the combination of As(?)and Cd(?);The oxidation performance and magnetic properties of Fe3O4@MIL-101(Fe)composites increased due to the introduction of Fe3O4,which were more conducive to the adsorption and adsorption recovery.It was expected to become the most promising heavy metal ion adsorbent.(2)When the background electrolyte is 0.001 mol L-1 of NaHCO3,the optimal adsorption conditions of MIL-101(Fe)for the initial As(?)concentration of 300 ?g L-1 were 95.38%.But the adsorption rate of As(?)in the actual water sample can only reach 79.26%;In the experiment of adsorption of As(?)in MIL-101(Fe),PO43-and SiO32-have a competitive effect on the adsorption of As(?).Others such as HCO3-,NO32-,Ca2+,Mg2+ can promote the adsorption of As(?).(3)The optimum adsorption rate of Fe3O4@MIL-101(Fe)composites for As(?)with initial concentration of 300 ?g L-1 was 98.00%.When Fe3O4@MIL-101(Fe)was applied to the actual water,the adsorption rate of As(?)was only 83.76%.In the experiments of As(?)in Fe3O4@MIL-101(Fe)adsorption water,HCO3-,PO43-,SiO32-have a competitive effect on the adsorption of As(?)in water.NO3-,SO42-,Ca2+,Mg2+can promote the adsorption of As(?).(4)The optimum adsorption rate of Fe3O4@MIL-101(Fe)composites for Cd(?)with initial concentration of 5 mg L-1 was 93.80%.However,in the actual water samples,the adsorption rate was 85.23%.The adsorption of Cd(?)in water was promoted by HC03-in Fe3O4@MIL-101(Fe)adsorption of Cd(?).And PO43-,SiO32-,Ca2+,Mg2+have a competitive effect on Cd(?)adsorption.(5)The three adsorption reactions are spontaneous,exothermic,entropy reduction process.They are conform to quasi-second-order kinetics model and Langmuir adsorption isotherm model.As(?)and Cd(?)can be adsorbed by MIL-101(Fe)and Fe3O4@MIL-101(Fe).