Construction And Structure-function Relationship Of Multi-functional Membrane

Due to the water pollution and energy issues,the separation membrane and battery separator become the research hotspots.At present,there are some problems for membrane in many aspects;for example,the selectivity-permeability needs to be further enhanced,the mechanism for the membrane formation and mass transfer in membrane should be explored deeply.To address these problems,more attention should be paid on the pore structure and interfacial properties of the membranes,which have the decisive effect on the membrane performance.In this thesis,based on the material-structure relationship,mechanism in membrane formation was proposed.According to these mechanisms,the membrane structure,and performance were adjusted precisely.The trade-off in the selectivity-permeability was common for the ultrafiltration(UF)membranes.Theoretically,this trade-off was mainly determined by the pore structure and interfacial properties of the membranes.Due to the excellent rigidity and high surface free energy,poly(m-phenylene isophthalamide)(PMIA)was used to fabricate the UF membrane via nonsolvent-induced phase separation.As the coagulation temperature increased,the pore size of the PMIA membrane raised from 6.26 nm to 8.73 nm,while the porosity increased from 5.65%to 9.23%.Through the selectivity-permeability analysis,the PMIA membrane was found to break through the trade-off between selectivity and permeability,attributed to the high porosity,narrow pore size distribution as well as the excellent hydrophilicity.This result indicated the validity of hypothesis,that is,the rigidity and surface free energy were crucial factors for membrane material.All these results suggested that PMIA was probably the most suitable materials for UF membrane.Apart from the excellent selectivity-permeability,PMIA membrane also has advantages in the fabrication of nanofiltration(NF)membrane via interfacial polymerization.Theoretical analysis suggested that the porosity/thickness ratio(?p/?)of the substrate has essential influence on the aqueous monomer concentration in the organic phase,and further affected the thickness of the polyamide film.To verify the proposed mechanism,the PMIA substrates with varied ?p/? were prepared and utilized to form the polyamide film under the identical interfacial polymerization conditions.As expect,the result confirmed our hypothesis that,along with the increase of?p/? value,the resultant polyamide film realized a decrease in thickness and a remarkable increase in the permeability without altering selectivity.Additionally,the wettability of the substrate can affect the surface morphology of the NF membrane,but has little impact on the membrane structure.For the first time,the correlation between the substrate and the polyamide film was elucidated and proved exactly.In order to deal with various mixtures,the pore size of NF membrane was adjusted via the various kinds of monomers.According to the physic-chemical properties of monomers and the parameters of the corresponding NF membrane,the effect of the monomer on the NF membrane structure can be qualitative explained.To precisely control the pore size of NF membrane,the model for interfacial polymerization containing bi-monomer was established.On the basis of this model,the pore structure and interfacial properties for NF membrane can be exactly predicted.Then,piperazine and diaminobenzenesulfonic acid were chosen as the monomers to fabricate the NF membrane via interfacial polymerization.As a result,the linear relation between parameters of NF membrane and theoretical production proved the validity of the model.NF membrane with tailored pore size has attracted a rapidly growing interest in various separation processes.Herein,tannic acid(TA)/Fe3+ complex,which was microporous amorphous material,was fabricated on the UF membrane via layer-by-layer technique.Through the strict control on the Fe3+ aggregation,the resultant TA/Fe3+ NF membrane has an average pore size of 0.8 nm,which was further confirmed by the molecular dynamic simulation.This result was in accordance with our expectation.In comparison with the membrane made by various materials,the TA/Fe3+ NF membrane obviously broke through the selectivity-permeability trade-off.This work provides a facile method to fabricate the NF membrane with tailored pore size designed at a molecular level.The separator for lithium ion battery can separate the electrodes and transfer lithium ions using the sub-micro pores.Recent researches demonstrated that the separator interface has important influence on the lithium ion transport properties.Herein,a novel class of carboxylated polyimide(PI)separator was proposed,which can be fabricated via an alkali treatment-based modification.The-COOH group can be easily introduced onto the surface/interface of the PI separator,without destroying its microstructure.Due to the unshared electron pairs,the-COOH group contributed to the desolvation of lithium ions,which facilitated the lithium ion transport rate.In contrast,the-COOH group will retard the transport of the anions via the hydrogen bond.Hence the lithium ion transference number was significantly improved in the carboxylated PI separator.On the basis of this mechanism,the-COOH group was found to increase the lithium ion transport rate by more than six times.Benefiting from the high lithium ion transport rate,the cell assembled with the carboxylated PI separator achieved high power and energy density.