The Adsorption Mechanism Of TpPa-1 And Its Modification On U(Ⅵ ) And Eu(Ⅲ)

Although nuclear energy has developed rapidly in the world as an efficient and clean energy source,the radionuclide pollution caused by uranium mining and nuclear waste disposal is also a problem that we must face,it will not only pollute water,soil and atmosphere,but also cause potential harm to human beings,animals and plants.Therefore,the control of radionuclide pollution in water environment is particularly important.In the face of this situation,the development of new removal materials and appropriate removal technology is urgently needed.Among them,adsorption technology is widely used for the removal of nuclides in water environment because of its simple operation and easy wide application;covalent organic framework materials（COFs）show great potential in environmental governance compared with traditional adsorbents due to their adjustable structure,unique hydrogen-bonding framework,high specific surface area and large adsorption capacity.This paper is mainly based on the COF-TpPa-1 of this new nanomaterial and the functional modification of it to prepare high performance derivative materials.The adsorption mechanism of radionuclide U（VI）/Eu（III）ions in water environment by TpPa-1 and nanocomposites was studied.The main research work and the corresponding research results can be summarized into the following three aspects:（1）TpPa-1 was used as an adsorbent to remove radioactive material U（VI）/Eu（III）ions from wastewater.After adsorption,the TpPa-1 was separated by filter membrane.The morphology,composition and structure of TpPa-1 were characterized by scanning electron microscope（SEM）,fourier transform infrared spectrometer（FT-IR）,X-ray powder diffraction（XRD）,transmission electron micros-cope（TEM）,nuclear magnetic resonance spectrometer（NMR）,thermogravimetric analysis（TGA）,surface area and porosity analyzer（SAP）,Zeta potential analyzer and X-ray photoelectron spectroscopy（XPS）,and the adsorption properties of U（VI）/Eu（III）ions in water were studied.The effects of solution p H value,reaction time,initial concentration of U（VI）/Eu（III）ions,temperature and ionic strength of U（VI）/Eu（III）ion on the TpPa-1 adsorption process were investigated.The adsorption data were fitted and analyzed by kinetic model and isotherm model.The results indicated that:the p H value has a great influence on the adsorption process,the optimum p H for the adsorption of U（VI）/Eu（III）ions was 6.5,the adsorption time reached equilibrium at about 4h;the increase of temperature promoted the adsorption ability of TpPa-1 to U（VI）/Eu（III）ions,and the adsorption process was less affected by the ionic strength.The adsorption kinetic data were more consistent with the pseudo-second-order kinetic model,and adsorption stage has multiple effects,including outer membrane diffusion and intraparticle diffusion;the isothermal model was more consistent with the Langmuir model,indicating the adsorption of U（VI）/Eu（III）on TpPa-1 was a monolayer adsorption.At p H=6.5 and 298 K,the maximum adsorption capacity of TpPa-1 was 1194.07 mg（U（VI））/g and 1107.63 mg（Eu（III））/g respectively.（2）Based on a mutual promotion strategy,a novel graphene oxide-synergized covalent organic framework（GO@TpPa-1）was obtained via an in-situ loading of a covalent organic framework materials（TpPa-1）on monolayer graphene oxide（GO）sheets.The GO@TpPa-1 was characterized by SEM、TEM、FT-IR、XRD、TGA、Zeta、SAP、Raman analysis（Raman）and XPS,and the adsorption mechanism of U（VI）/Eu（III）ions was studied.The results showed that TpPa-1 was successfully loaded on the GO surface,the morphology and structure of the GO@TpPa-1 not only make up the shortage of individual nanomaterials,but also provide sufficient adsorption space and contact area for the removal of nuclide ions.The effects of solution p H value,reaction time,initial concentration,temperature and ionic strength of U（VI）/Eu（III）on the GO@TpPa-1 adsorption process were investigated by batch tests,the utilization ability of GO@TpPa-1 in practical applications was explored through five desorption-adsorption cycle experiments.When p H=6.5,the adsorption effect was the best,and the adsorption time reached equilibrium at about60min/30min respectively,the pseudo-second-order kinetic model was more suitable for describing kinetic data,higher temperatures promoted the adsorption of U（VI）/Eu（III）ions;the correlation coefficient of isothermal adsorption Langmuir model was higher,which indicated that GO@TpPa-1 adsorption process of U（VI）/Eu（III）ions belonged to chemisorption,and at 298K,the adsorption capacity reached at 1532.35 mg/g（U（VI））and 886.44 mg/g（Eu（III））.（3）A new NH₂-MIL-125@TpPa-1 nanohybrid material was synthesized by a novel"seed growth method",mainly based on the Schiff base reaction between aldehyde of monomer and-NH₂groups on metal-organic frameworks（NH₂-MIL-125）,which exposed more active sites and improved the adsorption ability of U（VI）/Eu（III）ions.The experimental data were fitted by batch experiments using kinetic,isotherm and thermodynamic models to explore NH₂-MIL-125@TpPa-1 adsorption mechanism for U（VI）/Eu（III）ions.The results showed that the composite NH₂-MIL-125@TpPa-1had a good adsorption effect on U（VI）/Eu（III）ions,which was the best at p H=6.5 and had fast adsorption kinetics.The pseudo-second-order kinetic model and the Langmuir model can explain the adsorption data more reasonably,the intra-particle diffusion model showed that there were many stages in the adsorption process,and the thermodynamic parameters showed that the adsorption process was endothermic and spontaneous.Therefore,higher temperatures will promote the adsorption capacity of NH₂-MIL-125@TpPa-1.When p H=6.5,T=298 K,the data fitted by the Langmuir model showed that the hybrid materials NH₂-MIL-125@TpPa-1 had high adsorption capacity for U（VI）/Eu（III）.The above research results were of great significance to the treatment and restoration of radionuclide wastewater.