Study On Chlorine Resistance Of PIPD Nanofiber Reverse Osmosis Composite Film

Polyamide reverse osmosis composite membrane is widely used in commercial seawater desalination industries around the world due to its excellent water flux and high salt rejection rate.However,in the actual desalination process,there are problems such as poor stain resistance and susceptibility to active chlorine,which leads to a drop in separation performance and a significant reduction in service life.The existing modification methods mainly focus on the method of interfacial polymerization,chemical grafting or assembly using small molecular substances.Graft growth will cause some damage to the membrane,and most of the small molecules do not have reversible cyclic chlorine-resistant groups,which can not solve the problem of significant degradation of membrane performance in long-term operation.In this dissertation,PIPD nanofibers with cyclic chlorine-resistant groups and highly hydrophilic UIO-66 were combined with polyamide reverse osmosis membrane to prepare a series of modified polyamides with excellent separation performance and.chlorine tolerance and fouling resistance,Which has important theoretical and practical significance for improving the environmental adaptability of the membrane.PIPD nanofibers have an imidazole group with recyclable chlorine resistance,and also have excellent mechanical properties and chemical stability.UIO-66 has been widely used in the modification of nanofiltration membranes and reverse osmosis membranes due to its chemical stability and high hydrophilicity.In the modification of the membrane,it is a good choice to use these two functional nanomaterials to modify the polyamide reverse osmosis membrane.The PIPD nanofibers were prepared by swelling-ultrasonic stripping method.The effect of ultrasonic frequency on the size of nanofibers was investigated.It was found that 40 k Hz is the most suitable processing frequency to obtain nanofibers with diameter of 200-500 nm.The PIPD microfiber exfoliation was promoted by the addition of a strong protonic acid,and SEM was characterized to obtain a smooth surface nanofiber having a diameter of 100 nm to 200 nm when the amount of methanesulfonic acid added was 50%(w/v%).UIO-66 with a size of 100nm-150 nm was prepared by microwave method.The particle size and chargeability of UIO-66 are suitable as nano-material modified polyamide reverse osmosis composite membrane.Based on the above research,a series of modified polyamide reverse osmosis composite membranes C-PUM,L-PUM and IP-PUM were designed and prepared by coating method,layer self-assembly technology and interfacial polymerization method.To explore the effect of the amount of PIPD nanofibers and UIO-66 on the membrane separation performance,it was found that UIO-66 is proportional to the water flux and rejection of the membrane,while the nanofibers reduce the water flux of the membrane and obtain three kinds of separation performance evaluation.The optimal performance of the membranes C1,L1,M2 under the modification method can reach more than 20.643 L/m3·h·MPa,and the retention rate can be maintained above 97.21%;afterwards,chlorine resistance is applied to C1,L1 and M2.Evaluation,after 3000 ppm·h chlorine treatment,the water flux of the membrane increased by 120% and the retention rate was 95%.At the same time,SEM showed that the surface morphology did not deteriorate significantly,showing a very good chlorine resistance;Cyclic chlorine tolerance assessment and EDS characterization of membrane surface elemental content confirmed the ability of PIPD nanofibers to have chlorine resistance.