Preparation Of Graphene Aerogel-based Surface Li~+-imprinted Materials And Their Lithium Extraction Performance

With the rapid development of lithium in new energy,nuclear industry,aerospace and other fields,the supply and demand of lithium resources are becoming increasingly tension.There are a large number of lithium resources in salt lake brine.Therefore,it is of great significance to accelerate the development of lithium resources in salt lake brine.Adsorption method has a large application prospect in extracting lithium from salt lake brine because of its simple process,economic and environmental protection.However,it is difficult to separate and recover magnesium and lithium in most salt lake brines,and conventional adsorbents can not specifically recognize and separate lithium(Li⁺).In order to improve the specific recognition ability of adsorption materials,surface ion imprinting technology can be used to prepared the surface Li⁺-imprinted materials with selective adsorption ability.At present,most of the surface Li⁺imprinted polymer(IIP)materials are powder or granular materials,which are difficult to separate and recover due to serious solution loss in the adsorption process.In order to solve this problem,a kind of three-dimensional macroscopic IIP material,that is graphene aerogels(GAs)surface IIP material with stable structure,strong selective adsorption and regeneration,was designed and constructed in this paper.In the process of GAs carrier synthesis,the introduction of reducing agent can not only promote the self-assembly of graphene sheets to make GAs have strong structural stability,but also help to retain a large number of active sites to facilitate the construction of more adsorption sites in the imprinting process.And the effect of the reduction intensity of reducing agent on the structure and properties of GAs and GAs-based IIP was explored.Two kinds of GAs(DMF-Tris/GAs and DMF-TUD/GAs)were synthesized by liquid self-assembly using N,N-dimethylformamide(DMF)as auxiliary crosslinking agent,GO as precursor,and Tris and TUD as reducing agents,respectively.Then,the GAs-based surface ion-imprinted materials(IIP-DMF-Tris/GAs and IIP-DMF-TUD/GAs),with certain capability of separating and recovering Li⁺were prepared by surface ion-imprinted techniques using the DMF-Tris/GAs and DMF-TUD/GAs as matrix carriers,respectively.The specific research contents are as follows:1.DMF-Tris/GAs surface ion-imprinted material for selective lithium extraction.First,DMF-Tris/GAs with good hydrophilicity(contact angle:77.8°),stable mechanical properties(bearing 5000 times of its own weight)were synthesized using liquid-phase self-assembly technique with GO as precursor,Tris as reducing agent and DMF as auxiliary crosslinking agent;Second,KH570-DMF-Tris/GAs were prepared by modifying DMF-Tris/GAs with silane coupling agent KH570.And then,PMAA-DMF-Tris/GAs were prepared by modifying DMF-Tris/GAs with methacrylic acid(MAA).Finally,IIP-DMF-Tris/GAs with good hydrophilicity(contact angle:58.8°)and stable mechanical properties(bearing 5000 times of its own weight),were obtained using 2-hydroxymethyl-12-crown-4 coordinated with Li⁺as functional monomer,ethylene glycol dimethacrylate(EGDMA)as cross-link agent and azobisisobutyronitrile(AIBN)as initiator.The Li⁺-imprinted material has a certain separation performance with the selectivity coefficients of Li⁺relative to Na⁺,K⁺,and Mg²⁺of 4.75,2.71,and 1.9,respectively.After four cycles of adsorption and desorption,the adsorption capacity of Li⁺decreased by 12.0%.2.DMF-TUD/GAs surface ion-imprinted material for selective lithium extraction.In order to obtain ion-imprinted materials with more stable structure and easy separation and recovery,the DMF-TUD/GAs with good hydrophilicity(contact angle:72.8°),stable mechanical properties(bearing 10000 times of its own weight),were synthesized by self-assembly with GO as precursor under the reduction of TUD and the assistance of DMF and NH₃·H₂O.And then,KH570-DMF-TUD/GAs were prepared by modifying DMF-TUD/GAs with silane coupling agent KH570.Furthermore,PMAA-DMF-TUD/GAs were obtained by modifying KH570-DMF-TUD/GAs with MAA.Finally,IIP-DMF-TUD/GAs,with good hydrophilicity(contact angle:46.0°)and stable mechanical properties(bearing 10000 times of its own weight),were obtained using 2-hydroxymethyl-12-crown-4 coordinated with Li⁺as functional monomer,EGDMA as cross-link agent and AIBN initiator.The obtained Li⁺-imprinted material shows certain Li⁺separation performance.The selectivity coefficients of Li⁺to Na⁺,K⁺,and Mg²⁺were 10.0,5.71,and 4.0,respectively.After six cycles of adsorption-desorption,the adsorption capacity of Li⁺decreased by only 9.0%.In summary,the reduction intensity of reducing agent has obvious influence on the structure and properties of GAs and GAs-based IIP.The strong reducing agent is benefical for strengthening their structural stability,which can improve the adsorption capacity and selectivity of GAs-based surface imprinted materials.This paper can provide a theoretical and actual basis for the design and development of new lithium extraction materials.