| With the rapid development of industrialization and urbanization,radioactive wastewater and industrial wastewater containing heavy metal ions are not up to standard or are discharged in disorder,causing serious pollution to the water environment,which runs counter to the concept that lucid waters and lush mountains are invaluable assets.Metal-organic frameworks(MOFs)are porous materials composed of organic ligands and inorganic metal ions or metal clusters.Because of their high porosity,adjustable pore size and high specific area,MOFs show excellent performance in gas adsorption and separation and pollutant removal.Functionalized MOFs materials prepared by selecting flexible pyridine ligands and carboxylic acid ligands can effectively eliminate iodine pollution and remove toxic heavy metal ions.Therefore,in this paper,three functionalized MOFs were designed and synthesized for the adsorption and removal of iodine and heavy metal ions in aqueous solutions.The main results are as follows:(1)In view of the iodine pollution in radioactive wastewater,pyridine-4-methyl-3-{[4-(pyridine-4-methoxy)phenyl]azo}benzoate(L1)and 5-methylisophthalic acid(H2BDC)and Zn(NO3)2·6H2O were synthesized under solvothermal conditions to synthesize a layered MOF,{[Zn(BDC)(L1)]·1.5H2O}n.Using the strategy of sonication in solvent,it can be exfoliated into two-dimensional MOF nanosheets(4.4±0.1 nm in thickness)to increase the surface area and adsorption sites of MOF materials,thereby improving the adsorption efficiency and adsorption capacity for iodine.The adsorption capacity of 2D MOF nanosheets for gas phase iodine reached 3510.05 mg/g,and the adsorption capacity for iodine in aqueous phase reached 3704.08 mg/g,which exceeded most adsorbents.In addition,at a lower iodine concentration(25 mg/L),a relatively high removal efficiency(>98.30%)and fast adsorption kinetics were exhibited.The adsorption mechanism was systematically studied using Zeta potential,infrared spectroscopy,X-ray photoelectron spectroscopy and Raman spectroscopy,and it was found that a large number of azo,ester functional groups and aromatic rings supported on MOF nanosheets have high affinity for iodine.(2)Aiming at the problem of water pollution containing Hg2+,using pyridine-3-methyl-4-{[4-(pyridine-4-methoxy)phenyl]azo}benzoate(L2)and 4,4?-dicarboxylic acid-diphenyl ether(H2L3)was reacted with Cd(NO3)2·4H2O to prepare a functionalized Cd-MOF,[Cd(L2)(L3)·H2O]n.The azo group,ester group,ether group,etc.preset in the MOF material are used as adsorption sites to remove Hg2+.The adsorption experiment results showed that the adsorption effect was the best when the adsorbent dosage was 100 mg/L and p H=5,and the adsorption capacity reached 106.9 mg/g.The adsorption mechanism was studied by infrared spectroscopy,and it was found that the coordination between nitrogen-containing functional groups and ether oxygen atoms and Hg2+was the main reason for the adsorption and removal of Hg2+.(3)In view of the problem of Pb2+pollution in water,using pyridine-3-methyl-4-{[4-(pyridine-4-methoxy)phenyl]azo}benzoate(L2)and 1,3,5-tris(4-carboxyphenyl)(H3BTB)with Cd(NO3)2·4H2O to obtain a MOF with a porous structure,{[Cd3(BTB)2(L2)·2DMA]}n.The abundant N and O sites in the pores are used to adsorb and remove Pb2+.The experimental results show that without p H optimization,when the adsorbent dose is 100mg/L,the adsorption effect is the best,and the adsorption capacity reaches 500.01 mg/g,and for the solution containing Pb2+with an initial concentration of 10 mg/L,the removal efficiency can reach more than 91.4%within 120 minutes.The adsorption mechanism was studied by infrared spectroscopy.After the adsorption of Pb2+,the infrared characteristic peaks of C=O at 1635 cm-1and 1182 cm-1moved,which proved that the coordination between O site and Pb2+was the reason for the good adsorption performance. |
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