Construction Of Selective Ultrafast Transfer Channels In Lamellar Nanofiltration Membrane And Investigation Of Membrane Performance

Excessive discharge of organic solvent puts great pressure on the environment.Therefore,development of efficient and environmentally friendly recovery and treatment technology is urgently required.Organic solvent nanofiltration（OSN）is an original membrane separation technology driven by pressure,with the advantage of environmentally friendly,low cost and high efficiency.Especially,the two-dimensional lamellar membranes with fast molecular transfer and precise sieving properties has become an important direction for membrane technology.Stable and efficient transfer channels are the structure basis of high-performance lamellar membranes.However,its precise construction is a huge challenge.In addition,the mechanism and intensification process of molecular transfer behavior in lamellar membranes are still unclear.The construction of low-resistance transfer channels is urgent,and these are the fundamental problem that limit the further application of lamellar membranes.In this research,the key is to build the low-resistance transfer channels of lamellar nanofiltration membrane for enhancing the mass transfer process and evaluating the mechanism of molecular transfer in lamellar membranes.The performance of lamellar membrane is determined by the physical structure and chemical environment of transfer channel.Thereby,rigid Mo S₂ and functionalized g-C₃N₄ nanosheets were used as building blocks in this study.Based on regulation of physical structure and chemical environment,two low-resistance transfer channels are constructed for the interlayer transfer and cross-layer transfer of lamellar membrane,which significantly strengthened the solvent molecule transfer process.These strategies open avenues to rational construction of highly efficient transfer channels of novel lamellar membranes.The specific research content and main conclusions are as follows:（1）Construction of interlayer channels in lamellar membrane and transfer property intensification.Irregular rigid Mo S₂ nanosheets with different thicknesses（1-4 layers）and small lateral-size（～500 nm）were prepared by controlled ultrasound-assisted exfoliation method.Then,the loosely stacked lamellar membrane was fabricated by vacuum filtration.Different from the layer-by-layer stacked structure of traditional lamellar membrane,such stacking offers unique hierarchical transfer channels:narrow gaps（～1.8 nm）at the contacting edges of flakes and large cavities（～8.3 nm）among stacked flakes.The results show that the large cavities reduce the molecular transfer resistance,realizes rapid molecular transfer,and obtains an acetone permeance of above 5000 L m^-2 h^-1 bar^-1.The narrow gaps endow membrane with more than 90%rejection for dye molecules larger than 1.9 nm.Further,dynamic simulation results show that the flow resistance of the molecules in the fastigiated interlayer channels is significantly lower than that of horizontal channels.Furthermore,the transfer rate equation of such channels was established by analyzing the transfer performance of a variety of molecules,which initially revealed the mechanism of molecular mass transfer in this channel.（2）Construction of cross-layer channels in lamellar membrane and transfer property intensification.Based on the previous work,this work focuses on the investigation of structure regulation and transfer performance of cross-layer channels in lamellar membrane.The edges of g-C₃N₄ nanosheets were selectively grafted with hydrophilic（-OH）or hydrophobic（-OOCCH₃）groups to achieve functionalization.Then,they are used as building blocks to the lamellar membrane with accurate and controllable chemical environment in cross-layer channels.In this manner,the interlayer channels of these membranes have identical composition and structure,while the chemical environment of cross-layer channels is controlled by the grafting groups.The performance results show that the hydrophilic group functionalized g-C₃N₄-OH membrane realizes excellent performance for polar solvents:low-resistance transfer in interlayer channels and selective transfer through cross-layer channels.And the permeance are increased by over 170%than that in g-C₃N₄ membrane.While nonpolar solvents exhibit inhibited transport due to the repulsion from cross-layer channels.Naturally,the separation factor of mixed solvent was increased by 284%.Moreover,the membrane exhibits excellent structural stability.The above work systematically regulated the microstructure of the cross-layer channels in lamellar membrane,and realized the efficient control of the molecular selective transfer capability.In summary,the researchers provide fastigiated interlayer channels by preparing loosely stacked layered membranes to achieve rapid molecule transfer.Furthermore,based on the edge-modified nanosheets,the microstructure of cross-layer channel is precisely controlled to achieve selective efficient enhancement of solvent molecule transfer.These strategies would provide appropriate guidance and assistance for the design and preparation of high-performance lamellar membranes.