| In contemporary society,rapid industrialization has greatly changed our lives.However,unsustainable development also leads to serious energy shortage and environmental pollution.On the one hand,in order to meet the increasing energy demand,nuclear energy has gradually become an alternative energy due to its high power density and low carbon emissions.However,in the process of nuclear energy use,the proper disposal of radioactive nuclear waste is an urgent problem to be solved.On the other hand,water pollution has become an environmental concern,especially for organic dyes,whose toxicity and potential carcinogenicity have attracted widespread attention.Among many pollutant treatment technologies,adsorption is considered to be the most potential means of environmental remediation.For adsorption,the key lies in the choice of adsorbent.In recent years,covalent organic frameworks（COFs）have attracted great research interest from scientists due to their high specific surface area,tunable pore structure,and good thermochemical stability.At the same time,COFs can also specifically functionalize the backbone by pre-selecting appropriate building units or post-synthesis modification to obtain new properties.Therefore,COFs have broad application prospects as emerging solid adsorbents in environmental remediation.This paper mainly explores the design and synthesis of functional covalent organic frameworks for the capture of the radioactive element iodine in the environment and the adsorption and separation of the organic dye rhodamine B（Rh B）.The main research contents are as follows:（1）In Chapter 2,considering the high affinity of ion sites and electron-rich heterocyclic rings for iodine,we reasonably designed the polymer structure.Using potassium tetraphenylborate and nitrogen-rich cyanuric chloride as organic monomers,we successfully prepared two ionic covalent organic frameworks LNU-61 and LNU-63 by Friedel-Crafts alkylation.It is also used as solid adsorbents for iodine capture and storage.As expected,both LNU-61 and LNU-63 exhibited excellent adsorption capacity and fast adsorption kinetics during the vapor iodine capture due to the graded pore structure and abundant active sites of the polymers.The saturated adsorption capacities of the two materials for iodine are 2.39 g g-1（LNU-61）and 2.85g g-1（LNU-63）,respectively.It is worth mentioning that the polymer LNU-63 can efficiently and rapidly adsorb iodine from 1600 mg L-1 iodine in n-hexane solution,which is of great significance for the capture of iodine under high concentration conditions.In addition,we explored the adsorption mechanism between the polymer and guest iodine by thermogravimetric,infrared spectroscopy,powder X-ray diffraction,Raman spectroscopy and X-ray photoelectron spectroscopy,and proved that the adsorption of iodine by the polymer depends on the electron transfer mechanism,namely electrons flow from the electron-rich aromatic frameworks to the electron-deficient iodine.The above research results show that ionic covalent organic frameworks have very good application prospects in the field of radioactive iodine capture.（2）In Chapter 3,we replaced the metal ions in the polymer backbone,selected sodium tetraphenylborate and nitrogen-rich cyanuric chloride as building blocks,and successfully prepared two functional covalent organic frameworks LNU-62 and LNU-64 by Friedel-Crafts reaction,the obtained polymers showed high thermal and chemical stability,and can be used as efficient solid adsorbents to remove the organic dye rhodamine B（Rh B）from environmental sewage.Due to the large aromatic conjugated system,graded pore structure,and negatively charged skeleton of both polymers,LNU-62 and LNU-64 showed excellent adsorption capacity for the cationic dye Rh B,with the highest adsorption capacity of 404.2 mg g-1 and 473.2 mg g-1,respectively.Even under the condition of mixing dyes with different charges,the polymer can still achieve selective adsorption of the cationic dye Rh B,indicating that the polymer ionic backbone has very good charge selectivity.In addition,we explored the mechanism of interaction between the polymer and Rh B by Zeta potential and infrared spectroscopy,confirming that the adsorption process mainly relies on electrostatic interactions andπ-πinteractions.The above results indicate that the ionic covalent organic frameworks is very suitable for selective adsorption and separation of cationic dye Rh B,and is expected to be an ideal material for the removal of organic pollutants in wastewater. |
PDF Full Text Request