Application Of Porous Hafnium Phosphonate Metal Organic Framework In The Proton Conductors And Adsorption Of Uranyl

Metal-organic framework materials（MOFs）are a new type of organic-inorganic hybrid materials,which are crystalline materials with periodic network structure formed by self-assembly of transition metals and oxygen-or nitrogen-containing organic ligands.Because of its designability of structure and pores and large specific surface area and porosity,it has developed rapidly in the last 30 years.Because zirconium（IV）has the characteristics of high charge density and covalent bond polarization,zirconium and hard oxygen ligands have a higher affinity than other divalent metals.Because of their good chemical stability,carboxylic acid-based zirconium-based MOFs have become the most widely studied materials at present,and have extensive research and applications in catalysis,adsorption,drug transport and proton conductors.Hafnium and zirconium are in the fourth subgroup.The outer electronic structure is the same,the atomic radius is also very similar,and it has a higher charge density.Theoretically,it has better stability in combination with hard oxygen ligands,but at present,there are few studies on MOFs centered on hafnium.Besides,hafnium has a high fast neutron absorption cross-section,can improving radiation stability and safety in later applications,so this paper chooses hafnium as the metal center for constructing MOFs.According to Pearson hard and soft acid and base theory,the p K_a value of the phosphonate ligand is lower than that of the carboxylic acid ligand,so this article selects phosphonic acid ligands to replace the more previously studied carboxylic acid ligands to synthesize more stable MOFs materials.In summary,the ultra-stable hafnium phosphonate metal-organic framework materials has been synthesized.As the first case of hafnium based phosphonic acid with zero-dimensional metal cluster MOFs,it can exist stably in a wide range of p H and in most strong acid solutions.Therefore,it is applied to energy and environment.On the one hand,as a platform MOF,by doping ionic liquids and acids to compare the effects of different guest molecules on proton conductivity,it is found that ionic liquids have a greater effect on proton conductivity,which provides a reference for the subsequent design and development of new proton conductivity materials;On the other hand,it was applied to uranyl adsorption in strong acidic solution.It is found that PHOS-100（Hf）also has a certain removal effect on uranyl in low acidic solution of 1 M nitric acid,which provides a method and train of thought for the treatment and disposal of nuclear waste liquid.