Iodine Adsorption In Tetrathiafulvalene-based Covalent Organic Frameworks

The present circumstances of fossil fuel depletion and environmental degradation demands exploring alternative and sustainable energy sources.Nuclear energy is considered as one of the most promising energy sources due to its high energy density and low carbon emission.However,the rational disposal of radioactive waste from nuclear fission poses an urgent issue in the development of nuclear energy.Radioactive iodine(I¹²⁹ and I¹³¹)is a typical contaminant associated with nuclear fission,which can spread rapidly through the air with radiation effects up to 10million years(half-life of I¹²⁹ is 15.7 million years).Therefore,the recovery and treatment of radioactive iodine are of serious concern to researchers in the fields of energy,materials and environment.On the other hand,porous materials have been widely used in catalysis,energy storage,photovoltaics,medical treatment and separation due to their permanent porosity,high specific surface area and diverse functionalities.In recent years,Covalent organic frameworks（COFs）,which have the characteristics of crystalline materials such as long-range order,self-healing and anisotropy,as well as the unique properties of porous materials,are acknowledged as the center of attention after metal-organic frameworks（MOFs）by experts in the field of porous materials.Covalent organic frameworks are composed of light elements connected by strong covalent bonds and have excellent thermal and chemical stabilities.Based on the aforesaid characteristics,these materials have wider opportunities in the enrichment and recovery of nuclear waste under complex operating conditions and hence the exploration in this field is of great significance.In reference to huge technical demands in the development of nuclear energy and the strong performance advantages of the crystalline organic porous material,this study mainly explores the following aspects:In the second chapter,the author successfully synthesized a novel two-dimensional COF（JUC-562）with defective tth topology.Characterization techniques like PXRD,FT-IR,TGA,SEM,specific surface area analysisas well as relevant structural data obtained from Materials Studio 7.0 simulation software confirmJUC-562 as two-dimensional material with good crystallinity and notable stability.The material has a Tetrathiafulvalene（TTF）functional group which has specific chemical adsorption to iodine.Experimental data show that the material can significantly adsob iodine vapor via the synergistic action of physical adsorption and chemical adsorption.In the third chapter,the author thoughtfully selected a three-node amino secondary structure unit and 2,3,6,7-tetramethylphenyl tetrathiafulvalene to prepare a three-dimensional COF material with rarely reported ffc topology（JUC-561）.The accuracy of the material structure is verified by the analysis of experimental characterization data and the comparison of theoretical simulation data.JUC-561 has ultra-high specific surface area(S_BET=2359 m²g^-1),attributed to its interpenetrating channels in the three-dimensional direction and its composition of light elements.The unique three-dimensional structural advantages promote the better exposure of iodine molecule adsorption sites,coupled with the synergistic effect of physical and chemical adsorption hencecontributing to an exceptional capture effect.Under the conditions of ambient pressure and 335K,the adsorption capacity of JUC-561 to iodine vapor can reach 8.15g g^-1,and the adsorption kinetic rate is 0.69g g^-1 h^-1,which surpass all other materials reported so far.In summary,COFs have emerged as cutting-edge crystalline porous materials with a wide range of advantageshaving great application prospects and merits consideration in molecular capture and other aspects.This study is the first to propose and verify the mechanism of synergistic physical and chemical enhancement of iodine adsorption.This research creates fertile ground for tetrathiafulvalene-based COFsin the field of nuclear waste disposal and other exciting applications.