Study On The Precise Construction Of Electrostatic Atomization-Assisted Hierarchically Structured Nanofiltration Membrane

Organic solvent nanofiltration（OSN）,as a new type of pressure-driven membrane separation technology,has attracted widespread attention by virtue of its high efficiency and environmental protection characteristics.However,the Trade-off between permeance and selectivity and the structure stability of membranes have always been important factors restricting their further development.In response to the above problems,this study focuses on the structure regulation of membrane based on electrostatic atomization,aiming at precise construction of structure and intensification of transport process,to achieve superior molecular transfer and separation performance.On the one hand,an ultra-thin dense layer is formed on the top of a loose interlayer to construct a hierarchical polyamide membrane;on the other hand,metal-organic framework（MOF）nanosheets,as structural units,are atomized and deposited with Cu²⁺and tetrakis（4-carboxy-phenyl）porphyrin（TCPP）solutions synchronously,and the three are coordinated and assembled into a sandwich-shaped MOF membrane.The methods and strategies for precise structure construction and enhancement of molecular transfer characteristics are proposed,and the regulation rules of membrane structure are revealed,to provide new ideas for material design and performance enhancement for separation membranes.The details are summarized as follows:（1）Preparation of hierarchical polyamide membrane.Using polyethyleneimine（PEI）and trimesoyl chloride（TMC）as reactive monomers,by controlling the ratio and amount of water/oil phase monomers,a hierarchically structured polyamide membrane was precisely constructed,where an ultra-thin dense layer was formed on the top of a loose interlayer.The loose layer with low crosslinking degree reduces the molecular transfer resistance and compensates for the microporous structure of substrate,supporting the formation of ultra-thin and dense layer.The dense layer achieves efficient rejection,and the ultra-thin structure shortens transport path to minimize the sacrifice of molecular permeation.The two synergistically strengthen the molecular transfer and separation characteristics.The thickness influence mechanism of dense layer in hierarchical structure on molecular transfer was also explored.The results show the hierarchical polyamide membrane with a 13.8 nm-thick dense layer readily realizes ultra-fast solvent permeation(acetone permeance reaches 56.9 L m^-2 h^-1 bar^-1)and complete rejection for acid yellow 14（1.9 nm）,and shows good structure stability and long-term operation stability.（2）Construction of hierarchical MOF membrane.2D MOF nanosheets wereprepared by surfactant-assisted method with Cu²⁺and TCPP precursors.Then,MOF nanosheets,as structural units,were atomized and deposited with Cu²⁺and TCPP solutions synchronously and independently,constructing hierarchical MOF membrane.The binding sites exposed by the orderly tiled stacking of MOF nanosheets were reassembled with precursors;meanwhile,Cu²⁺and TCPP in interlamination were coordinated with each other,assembling cross-linked MOF networks;the alternate stacking of nanosheets and cross-linked networks builds a sandwich hierarchical structure,enhancing the stability.The results show the hierarchical MOF membrane can maintain intact structure after 10 min of ultrasonic treatment and immersion for 2months.In addition,defined amount of precursors accurately governs membrane thickness,and continuous cycle operation ensures area of 22×33 cm².Meanwhile,the high specific surface area and porosity of MOF materials enable water permeance to reach 186.0 L m^-2 h^-1 bar^-1,and the precise pore structure achieves a 95%rejection for dyes larger than 1.2 nm in size.