Study On The Preparation Of Crown Ether Modified Chitosan Composites And The Selective Separation Of Lithium Ion

Lithium an important energy metal.As an important strategic resource,lithium accounts for a large proportion of our economic development,political prosperity and military construction.With the full rise of new technologies and new industries,the diversified application of lithium resources has accelerated the rapid development of the lithium market.In view of the simple reaction process and low production cost of the adsorption method,it has gradually become the most ideal method for extracting lithium from salt-lake brine.The macrocyclic structure is a unique property of crown ether compounds.Crown ether shows excellent ability in the adsorption and separation of lithium ions.However,small-molecule crown ethers usually have certain toxicity and are not easy to separate from the system.Crown ethers are used as organic ligands to bond to various matrix materials in the form of chemical bonds to prepare organic ligand-composite adsorption materials.This is a hot spot in the research and development of lithium extraction by adsorption in recent years.Chitosan shows an outstanding contribution to the field of metal ion adsorption due to its wide sources and environmental protection.However,chitosan also has disadvantages such as unsuitable recovery,easy agglomeration and low specific surface area.In this thesis,through choosing different methods,the crown ether and its derivatives are fixed on the chitosan matrix material in order to achieve the purpose of preparing crown ether modified chitosan composite materials,and further explore the mechanical properties of the material and its effect on lithium.The adsorption mechanism of ions.The main research contents of this topic are as follows:（1）We successfully prepared a crown ether modified chitosan nanofiber membrane（CS-CE）with a high specific surface area through a simple and environmentally friendly low-temperature phase separation method.We performed the characterization analysis and the adsorption experiment analysis on the material.The results showed that the specific surface area obtained by the BET test is 111.55 m² g^-1,and the highest adsorption capacity at p H=7.0 is 297 mg g^-1.In addition,in the presence of other interfering metal ions,the selectivity of CS-CE to lithium ions（Li⁺）was still very high,and the separation coefficient（α）was between 1.33 and34.05.After 5 cycles of regeneration experiments,the maximum adsorption capacity of CS-CE remained 91.2%.All results showed that CS-CE could be used for the selective adsorption of lithium.（2）We adopted a step-by-step method,combined with crown ether（CE）modified functionalized graphene oxide（GO）,chitosan（CS）and polyvinyl alcohol（PVA）macromolecular materials,and successfully prepared the GO-CE-CS-PVA nanofiber membrane with excellent performance through low-temperature thermally induced liquid-liquid phase separation technology.The nanofiber realized the high-efficiency selective adsorption and separation of Li⁺.The specific surface area of the GO-CE-CS-PVA nanofiber membrane was as high as 101.5 m² g^-1.A series of static and dynamic adsorption experiments and simulated adsorption results of actual interference ions showed that the maximum adsorption capacity of the GO-CE-CS-PVA nanofiber membrane could reach 168.50mg g^-1 at p H=7.0.In addition,the excellent selective adsorption of Li⁺and good reusability were the affirmation of the stability of GO-CE-CS-PVA nanofiber membrane,which also made it more valuable in the application of lithium extraction from salt-lake brine.（3）We designed and synthesized a pseudo-crown ether monomer（TEG4MEC）,and successfully grafted it on the surface of cross-linked chitosan（CCS）microspheres through an initiator.From the results of a series of static and dynamic adsorption experiments,compared with the unmodified CCS microspheres,the adsorption capacity and adsorption kinetics of CCS-TEG4MEC microspheres for Li⁺are greatly enhanced.The maximum adsorption capacity of Li⁺on CCS-TEG4MEC microspheres obtained by Langmuir isotherm fitting is 156.16 mg g^-1.In addition,CCS-TEG4MEC microspheres also showed effective regeneration performance and highly stable adsorption capacity,which can be reused.