Engineering Design Of Covalent Organic Framework Membranes Toward Liquid Mixture Separations

Membrane technology is rapidly-developed and commonly-used for a broad spectra of applications,such as water resource,energy and environment.Recently,covalent organic frameworks（COF）featured with rigid,long-range ordered,easily-tailored pore/channel structures at molecular scales,have exhibited tremendous potentials in membrane technology for liquid mixture separation.In this study,based on engineering design of COF membranes,we proposed aqueous two-phase interfacial assembly,Br?nsted acid mediated control and confined cascade separation,to solve the challenges of hard processability,difficulty in crystalline structure manipulation and low separation precision for COF membranes.Accordingly,we achieved precise contruction of COF membrane structures and efficient intensification of COF membrane process for liquid mixture separation.The contents were descripted in brief as follow.1.Bassed on phase engineering,aqueous two-phase interfacial polymerization was constructed to fabricate COF membranes.The aqueous two-phase assembly strategy was also the first example of fabricating membranes without any organic solvent.Moreover,with optimizing interfacial tension of aqueous-two phase,the film-formation ability of COF was successfully manipulated.The relationship between interfacial tension and film-formation ability was further developed to gain insight into structure evolution of COF membranes.Under low interfacial tension（0.10-1.0 m N/m）,the resultant cationic COF membranes exhibited 1.7-3.7 L m^-2 h^-1 bar^-1of water flux and93.0%-93.6%of Na Cl rejection,which were superior compared with the state of art desalination membranes.2.Based on mediator engineering,Br?nsted acid was used as mediator to control structural evoluation of COF membranes,which contributed to the facile manipulation of crystallinity,thickness and aperture at angstrom scale of COF membranes.The relationship between partition coefficient（log P）of Br?nsted acid and crystalline structural evolution of COF membranes was also developed.By tuning partition coefficient（log P）under 1.0-3.0,the resultant non-ionic COF membranes demonstrated10.57 kg m^-2 h^-1 of total flux and 5534 of n-butanol/water separation factor,which had a superior performance compared with the state of art membranes.3.Based on nanochannel engineering,the concept of“confined cascade separation”was proposed to fortify the presicion of COF membranes for ionic separations with small components.A set of descriptors of stage properties,including hydration energy,group density,group distance and stage number,were tuned to elucidate their effect on confined cascade separation for ionic transport.The de novo designed anionic COF membranes achieved breakthrough in monovalebt cation separations,acquiring an actual selectivity of 4.2-4.7 for K⁺/Li⁺binary mixtures and an ideal selectivity of 13.7-16.4 for K⁺/Li⁺,which were superior to ever-reported membranes.