Preparation Of MOFs/Graphene Oxide Composites For Selective Adsorption Of Rare Earth Ions

Rare earth elements have been widely used in various fields due to their excellent physical and chemical properties.Rare earth elements and their similar radii make each element have very similar physical and chemical properties,and the purification of a single rare earth element is not easy.However,industrial applications have high requirements on the purity of rare earths.Therefore,the separation of rare earth elements is an urgent problem to be solved in the industry.Although a variety of adsorbent materials have been developed for the adsorptive separation of rare earth elements.But most of them are difficult to achieve high adsorption capacity and high separation selectivity at the same time.Since metal organic frameworks（MOFs）are extremely sensitive to the change in the radius of rare earth ions during the crystallization process,MOFs materials have high selectivity to rare earth elements.Therefore,in this paper,graphene oxide（GO）with high adsorption capacity for metals was selected as the matrix material,combined with MOFs materials with high selectivity for rare earth ions,MOFs/GO nanocomposites were synthesized.It is used to explore the selective adsorption of trace rare earth elements in water by adsorbent materials.This thesis is mainly divided into the following parts:1)We selected graphene oxide（GO）with high adsorption capacity as the matrix material,with Zr⁴⁺as the MOF metal center and fumaric acid（FUM）as the organic ligand.MOF-801/GO composites were prepared by a one-pot method.We found that Zr-FUM/GO composites have good stability under acidic conditions.The adsorption mechanism is mainly through the synergistic effect of the porous nature of the composite material and the abundant oxygen-containing groups on the surface.The difference in the size of the adsorption pore of the material and the difference in the binding force of the surface groups to different rare earth ions resulted in the selective adsorption of rare earth ions by the composite materials.The maximum adsorption capacity of Zr-FUM MOF/GO for 15 mixed rare earth ions such as La is about 40.08mg/g.Compared with single Zr-FUM MOF,the adsorption capacity of Zr-FUM MOF/GO composite for rare earth ions is significantly increased.And the composite material can still maintain high selectivity to Sc and other rare earth ions.2)Zr⁴⁺is used as the metal center of the MOF,terephthalic acid（H₂BDC）and trimesic acid（H₃BTC）are used as organic ligands,and GO is used as the matrix.One-pot synthesis of MOF-808/GO composites by microwave method,and one-pot synthesis of UIO-66/GO composites by solvothermal method.By comparing the Zeta potentials of Zr-MOFs under different ligand environments,materials with more potential for metal adsorption were selected.We found that the surface of GO composited with Ui O-66 MOF contained more carboxylic acid groups.This makes the material easier to produce protonation reaction during the adsorption process,which is more conducive to the adsorption of rare earth ions.Through adsorption experiments,we found that the maximum adsorption capacity of Zr-BDC MOF/GO composites for rare earth ions is about 420.94 mg/g,but the selectivity between rare earth ions still needs to be improved.3)The material uses Zn²⁺as the MOF metal center,terephthalic acid（H₂BDC）as the organic ligand,and GO as the matrix.The interlayer confined strategy was used to control the growth of Zn-hydrotalcite between GO layers to construct a Zn-hydrotalcite/GO composite;it was immersed in DMF dissolved in terephthalic acid（H₂BDC）;Zn-BDC MOF/GO composites.The adsorption capacity of the material for 11 miscellaneous rare earth elements is up to 344.48 mg/,and it shows better selective separation performance between early lanthanides and late lanthanides.Compared with previously reported materials for the adsorption and separation of rare earth ions,our prepared Zn-BDC MOF/GO composite possesses both high adsorption and high selectivity for rare earth ions.