Research On The Structures And Surface Properties Of Reverse Osmosis Membrane Separation Based On Porous Materials

Reverse osmosis（RO）has been regarded as the predominant desalination strategy to obtain fresh water from seawater and brackish water to address the water-scarce problem in the whole world.Polyamide-based composite reverse osmosis membrane prepared by interfacial polymerization has been commercialized and extensively employed in RO plant due to high salt rejection,comparable water permeability,stable performance and scalable membrane fabrication process.However,the"trade off"effect between the permeability and the rejection rate of the RO membrane,and the poor fouling resistance and oxidation resistance seriously restrict the improvement of the performance of the PA-RO membrane.The addition of inorganic nanomaterials into the PA layer brings hope to solve the problem.In this paper,based on the interfacial polymerization technology,functionalized carbon nanotubes and core-shell mesoporous hybrid nanospheres were respectively incorporated into the PA separation layer to fabricate a PA-based nanocomposite reverse osmosis membranes with high flux,high selectivity,fouling resistance and stable performance.At first,functional composite carbon nanotubes/polyamide nanocomposite reverse osmosis membranes were prepared by introducing modified carbon nanotubes into the polyamide separation layer.Carbon nanotubes were functionalized with tannic acid（CNT@TA）,and silver nanoparticles were embedded in the pore channels of CNT@TA（Ag-CNT@TA）.CNT@TA and Ag-CNT@TA were respectively added into the PA layer by interfacial polymerization using trimesoyl chloride（TMC）as an organic phase and meta-phenylene diamine（MPD）as an aqueous phase.The results show that the functionalized CNTs can be uniformly distributed in the PA matrix with random orientations.A loose PA separation layer was obtained by introducing CNT@TA.Correspondingly,abundant new water channels were formed.Compared with the pure PA membrane(3.21 L·m^-2·h^-1·bar^-1),the water permeability(4.81 L·m^-2·h^-1·bar^-1)of the nanocomposite membrane is enhanced by 49.8%without any loss in Na Cl rejection（99.3%）.The membrane exhibits satisfactory chemical-and bio-fouling resistances.The confined structure effectively avoids the leaching out of the Ag nanoparticle and keeps the persistence of the antibacterial property.The excellent compatibility between the CNTs and polyamide matrix endows the membrane with long-term performance stability.In order to further improve the performance of the reverse osmosis membrane,a mesoporous core-shell hybrid nanosphere/semi-aromatic polyamide nanocomposite reverse osmosis membrane was fabricated.The yolk-shell mesoporous hybrid nanospheres（YSHNs）were synthesized by a co-assembly strategy.Then,silver nanoparticles（Ag NPs）were uniformly embedded in the hollow cavities（Ag-YS）.YSHNs and Ag-YS were aminated（YS-NH₂and Ag-YS-NH₂）.The YS-NH₂or Ag-YS-NH₂nanosphere incorporated semi-aromatic polyamide（SAP）membrane was successfully fabricated using 1,3,5-cyclohexane tricarbonyl chloride（HTC）as an organic phase,meta-phenylene diamine（MPD）as an aqueous phase,and the mesoporous hybrid spheres as nano-additives by an interfacial polymerization approach.The results show that nanospheres were successfully incorporated into the PA separation layer.The membrane incorporated with YS-NH₂nanospheres exhibits ultrahigh pure water permeability(PWP,9.34 L·m^-2·h^-1·bar^-1)and water permeability(8.18 L·m^-2·h^-1·bar^-1)with comparable Na Cl rejection（96.1%）.The aminated spherical surface improves the interfacial compatibility between PA matrix and the YSHN nanospheres refraining from the formation of the nonselective defects.Furthermore,the flexible YSHN hybrid structure and the mesoporous core would play an important buffering for avoiding the shell fracture under a high operation pressure.The confined Ag NPs in the YSHNs mesostructure endow the membrane with a sustainable antibiofouling property.Moreover,the polylysine（PL）modification dramatically improves the membrane fouling resistance and performance stability.This research provides a new insight for fabricating high-permeable polyamide-based membrane.