Fabrication And Characterization Of One-dimensional Nanochannels Contained Thin-film Composite Membranes

At present,reverse osmosis(RO)and nanofiltration(NF)technologies are widely used in seawater desalination and water reuse.Although the current commercial thin film composite(TFC)RO/NF membrane already has a great separation performance,it is extremely important to further improve its permeability.In recent years,a new method of modifying TFC membranes has been published.Generating nanovoids in the polyamide selective layer of the TFC membranes,and the nanovoids have indeed greatly improved the separation performance.However,they did not explore the influence of the size and dimensions of the nanovoids on the separation performance.In order to explore the above question,we improved the zero-dimensional(0D)nanovoids one-nanochannels(1D),and fabricated the 1D nanochannels contained RO and tight NF membrane,respectively.At the same time,we conduct an in-depth analysis of the experimental phenomena encountered in our work.The specific work is as follows:(1)We applied a template-assisted etching method to fabricate 1D nanochannels in the polyamide layer of RO membrane.For comparison,we used the similar method to prepare the TFC RO membranes with OD nanovoids.Compared with the control TFC RO membrane,the TFC-0D membrane only showed a 61%higher water flux,while the TFC-1D membrane exhibited a significant 126%higher water flux without a significant decrease of NaCl rejection,which was due to the increased dimension of the nanovoids.This method provides a novel route for the preparation of the new generation RO membranes with high-performance.(2)The excessive nanovoids/nanochannels formed in the rejection layer of TFC membranes will cause defects and reduce the selectivity.Here we report a second interfacial polymerization method to fabricate a loose poly(piperazineamide)layer on the original tight poly(m-phenylenediamineamide)layer.The defects caused by the 1D nanochannels were repaired and the membrane has a dramatically improved salts rejection.Meanwhile,the second interfacial polymerization reduces the density of the overall selective layer.Compared to the IP-1D-10 membrane,the IP-1D-10 membrane has a 66%higher pure water flux(32.7 ±2.6 L m-2 h-1).In addition,the separation performance can be adjusted by the number of nanochannels to adapt to the specific industrial process.(3)During the above work,we found that the complex fabricated by Cu2+and MPD has the potential to be used for preparing NF membranes.Therefore,we mixed MPD with polyethyleneimine(PEI)and prepared a long-chain complex through the complex reaction with Cu2+.Then,a novel complex NF membrane was prepared by electrostatic spraying.The positively charged complex NF membrane has a high rejection to MgCl2(nearly 98%).This work provides a new direction for exploring new materials for preparing TFC NF membranes.