Soft Template Strategy Prepared Anion Exchange Membrane For Electrodialysis Application

As one of the membrane desalination technologies,electrodialysis（ED）has the advantages of high efficiency,low cost and zero carbon emission for desalination of brackish water.It can be combined with other membrane desalination technologies and new power generation technologies to effectively reduce the cost of seawater desalination.As one of the core components of electrodialysis device,anion exchange membrane（AEM）needs to have high permselectivity and low area resistance.The permselectivity of the membrane is mainly affected by the concentration of fixed charge groups,and the area resistance is affected by the ion conductivity of the membrane.In this thesis,a soft template strategy is proposed to promote the formation of the microphase separation structure inside the anion exchange membrane.Specifically,poly（2,6-dimethyl-1,4-phenylene oxide）with good stability and low cost was designed as polymer backbone;multi-cation side chains with high local density of fixed charge groups are introduced to improve the permselectivity of membranes.Small-molecule soft templates were used to promote the microphase separation structure to improve the ion conductivity and reduce the area resistance of the membrane.The influence of different type soft templates on the comprehensive performances of the membranes was explored,and the main contents are as follows:Construction of ion transport channels by soft template strategy based on electrostatic force.Firstly,the poly（2,6-dimethyl-1,4-phenylene oxide）was brominated,and multi-cation side chain（Tri-QAs）were prepared by a two-step method.Next,the Tri-QAs side chains were grafted on the poly（2,6-dimethyl-1,4-phenylene oxide）backbone through the Menshutkin reaction.Finally,different amounts of 1,2-ethanedisulfonic acid（EDA）were added in TPPO-2S-0 membrane,TPPO-2S-x membranes were obtained after water treatment.The multi-cation side chain can increase local density of fixed charge groups to improve the permselectivity of the membranes;the sulfonic acid groups in the soft template can induce the quaternary ammonium groups in the side chains to form ion domains through electrostatic interaction.The TPPO-2S-1 membrane with soft template of 1 wt.%has transport number of 0.98,area resistance of 1.78Ωcm²,current efficiency of 92.90%,and energy consumption of 4.08 k Wh kg^-1.Soft template strategy enhances polarity difference and promotes the formation of microphase separation structure.The multi-cation functionalized poly（2,6-dimethyl-1,4-phenylene oxide）membranes were prepared by Menshutkin reaction.N¹,N¹,N¹,N³,N³,N³-hexamethylpropane-1,3-diaminium（3-2N⁺）,N¹,N¹,N¹,N⁴,N⁴,N⁴-hexamethylbutane-1,4-diaminium（4-2N⁺）,and N¹,N¹,N¹,N⁶,N⁶,N⁶-hexamethylhexane-1,6-diaminium（6-2N⁺）were introduced to further strengthen the polymer polarity difference and promote the formation of microphase separation structure.By adjusting the size and type of soft template,TPPO-n-2N⁺-x membranes were prepared and applied to electrodialysis desalination.The TPPO-6-2N⁺-2membrane gives the transport number of 0.94,area resistance of 1.96Ωcm²,the highest current efficiency of 93.16%,and energy consumption of 4.25 k Wh kg^-1.