Investigation On The Preparation Of MOFs-based Nanoscale Materials And Its U(?) Removal Properties

Recently,the widespread usage of nuclear energy has inevitably caused the discharge of nuclear waste containing large amount radionuclide with high radioactivity properties,which has great threat to human health and environment.Therefore,it is a key issue in environmentally friendly and healthy development of nuclear energy.In this paper,Metal organic frameworks(MOFs)were used as the precursors and templates to synthesize different adsorbents with high specific area and rich surface functional groups,including polydopamine nanomaterials(ZIF-67@PDA),hollow structure layered double hydroxides(LDHs)(ZIF-67@LDH)and single metal oxyhydroxides(NO3-LDH,Br-LDH and C104-LDH)intercalated with different anions.U(?)removal mechanisms by different MOFs derived adsorbents are detailly investigated by batch experiments combined with different spectral analysis techniques.The research methods and conclusions are as follows:(1)Using ZIF-67 crystal as a template,ZIF-67@PDA material was synthesized in an aqueous solution of dopamine hydrochloride.The functional groups containing abundant oxygen and nitrogen on the surface can offer effective active sites for U(?).The saturated adsorption capacity for U(?)is 175.82 mg·g-1 at pH=4.5,and the adsorption equilibrium can be quickly reached within 60 minutes.Batch experiments and spectral analysis prove that the removal of U(?)mainly depends on the complexation of hydroxyl and amino groups on the surface of the material.(2)Using ZIF-67 as the precursor and the alcohol solution of nickel nitrate as the etchant and raw material,the binary ZIF-67@LDH with a hollow structure was synthesized.It has a mesoporous and microporous structure with the specific surface area of 109 m2·g-1,which is conducive to the U(?)diffusion and adsorption on the material.The saturated adsorption capacity of U(?)is 326.04 mg·g-1 at pH=4.5,and the adsorption process is a spontaneous endothermic reaction.This material maintains a high removal efficiency for U(?)in a wide pH range of about 5.0?8.0,and the removal effect is almost not affected by ionic strength,indicating that the adsorbent and U(?)are mainly combined in the form of inner spherical surface complexation.Combining spectral analysis,it proves that the removal of U(?)mainly depends on electrostatic adsorption and complexation of U(?)with hydroxyl functional groups.(3)Using anionic cobalt salts(i.e.,cobalt nitrate,cobalt bromide and cobalt perchlorate)as an etching agent and ZIF-67 as the precursor,respectively,flake-like NO3-LDH,Br-LDH and ClO4-LDH were synthesize respectively.The interlayer spacing of the materials can be changed by inserting different anions.The layer spacing(d003)is in the order of ClO4-LDH(0.878 nm)>NO3-LDH(0.781 nm)>Br-LDH(0.750 nm).The saturated adsorption capacity of ClO4-LDH was 1357.41 mg·g-1,and it has better recycling performance.Spectral analysis proves that the wide interlayer spacing in LDHs and abundant hydroxyl functional groups on its surface are more conducive to removal U(?)by diffusion adsorption and complexation effect.In summary,this research successfully synthesized a variety of materials by using MOFs as templates and precursors.The series of MOFs-based materials synthesized in this study have shown a certain potential in the treatment of uranium-containing wastewater,which can provide a certain reference basis for the basic research of radioactive wastewater purification and nuclide enrichment.In addition,the method used in this research is efficient and controllable,which could provide a reference for LDHs synthesis.