High-efficiency Nanocomposite Reverse Osmosis Membranes Containing Interfacial Water Channels For Desalination

Highly efficient seawater desalination technology with a polyamide reverse osmosis membrane as the core is the key to address the problem of shortage of fresh water resources.However,the traditional cross-linked polyamide molecular structure of the desalination membrane limited the improvement of filtration efficiency,resulting in a "bottleneck" problem in the development of polyamide reverse osmosis membranes.In this study,a reverse osmosis membrane with a cross-linked polyamide as the barrier layer was fabricated by interfacial polymerization of trimesoyl chloride(TMC)and m-phenylenediamine(MPD)on a highly porous electrospun nanofiber substrate.Meanwhile,nanocellulose after chemical modification on the surface was introduced into the cross-linked polyamide molecular structure of the membrane.As a result,interfacial water channels were created between the bulk structure of cross-linked polyamide and the surface of nanocellulose,which promoted the rapid transmission of water molecules to improve the water flux of the membrane.Therefore,a new type of thin-film nanofiber composite(TFNC)reverse osmosis membrane with interfacial water channels was prepared.The excellent desalination performance of the membrane was demonstrated for brickash water desalination.Basically,nanocellulose derived from the bamboo was fabricated by oxidation of 2,2,6,6-tetramethylpiperidine-l-oxyl(TEMPO)and sodium periodate oxidation system,and dialdehyde nanofibers(DANC)was obtained.Furthermore,a series of hydrophobic nanofibers grafted with different alkyl chain lengths were prepared by the Schiff base reaction of the aldehyde groups on the surface of DANC and amino groups of the substituents.The hydrophobic nanocellulose was then introduced into the interface polymerization system,as a result,the interfacial water channels were constructed in the cross-linked polyamide structure.The size of the interfacial water channels was adjusted by different alkyl chain length to achieve the goal of desalination of brackish water with a high efficiency.The structure and morphology of nanocellulose and cross-linked polyamide reverse osmosis membrane were fully characterized by various characterization methods such as ATR-FTIR,TG,TEM and SEM.At the same time,the desalination performance of the new cross-linked polyamide reverse osmosis membrane was investigated and was compared with that of traditionally commercial reverse osmosis membranes.It shows that the highly efficient nanocomposite reverse osmosis membrane exhibited a permeation flux of 37.9 L/m2h and a rejection ratio of 98.7%,which confirmed that the interfacial water channels could significantly increase the permeation flux of the membrane while remaining a high rejection ratio as well.Compared with traditionally RO membranes,the permeation flux of the nanocomposite RO membrane can be increased by two times while maintaining the same rejection ratio of 97.5%.