Modification Of Metal Organic-frameworks MIL-101 And Their Adsorption For Radioactive Iodine

Nuclear energy is a highly efficient and clean energy.However,public opinion is so hostile to building new nuclear power stations because of a series of nuclear accidents.Radioactive iodine is one of the inevitable products of a nuclear accident.To prevent harm to humans and the environment,radioactive iodine must be quickly and efficiently adsorbed.In this paper,MIL-101 which has a high specific surface area,tunable channels and excellent stabilities was chosen as a based material.MIL-101 was modified by doping of copper nanoparticles and etching.After then,the structure and morphology of the material and its adsorption properties of I2 were investigated.(1)MIL-101 was synthesized by hydrothermal method,whose BET specific surface area is 3134 m2/g after being purified by DMF and anhydrous ethanol.The structure and morphology of the samples were characterized by XRD and SEM etc.The results showed that the crystals of MIL-101 are octahedral structure with good dispersibility and uniform size.MIL-101 has a good adsorption property for I2.The saturated adsorption capacity of MIL-101 to iodine vapor and iodine/cyclohexane solution is 342 wt%and 385 mg/g,respectively.In addition,the adsorption of MIL-101 to I2 belongs to physical adsorption,and it showed an excellent reversible adsorption of iodine.MIL-101 has a cycle ratio of 60%after five cycles.(2)In order to improve the adsorption capacity of MIL-101 for I2,Cu/MIL-101 nanocomposites were synthesized by doping copper nanoparticles into MIL-101.The resulting samples were characterized by SEM.XRD,EDS,TEM and ICP etc.The results showed that the structure and morphology of the based material MIL-101 had no obvious change at low loading content of Cu nanoparticles,but part of the crystal structures of MIL-101 collapse at high loading content of Cu nanoparticles.In addition,the BET specific surface area and pore volume of MIL-101 decreased with increased loading of Cu nanoparticles.The doping of Cu nanoparticles increased the electrostatic gradient of the adsorbent,which enhanced the electrostatic force on I2.The saturated adsorption capacities of the adsorbent to I2 were increased to approximately 342 wt%and 432 mg/g,respectively.In addition,compared with MIL-101,Cu/MIL-101 nanocomposites not only had reversible adsorption of I2,but also exhibited more excellent cyclicity.In the first three adsorption cycles,more than 90%of the adsorption capacity was maintained.(3)In order to improve the adsorption capacity of MIL-101 for I2,the pore structure of MIL-101 was etched.After etching,the crystal surface of MIL-101 became rough.In addition,etching had no significant effect on the structure and stability of MIL-101,but caused the decreasing of specific surface area and increasing of pore volume.According to the iodine-benzene adsorption theory,increased pore volume exposed more benzene rings and provided more adsorption sites,increasing the saturated adsorption capacity of adsorbent to iodine vapor to approximately 371 wt%.Due to the hydrogen ion etching,the hydrophobicity of the adsorbent was increased,so that the saturated adsorption capacity of iodine/cyclohexane solution was increased to approximately 980 mg/g,which was 155%higher than that of MIL-101.In addition,compared with MIL-101,ED/MIL-101 not only had good reversible adsorption of I2,but also can completely adsorb iodine from a low-concentration solution.