Study On The Preparation And Water Molecular Mass Transfer Process Of Aquaporin Forward Osmosis Composite Membrane

Polyamide composite film has been widely used in the field of forward osmosis membrane separation technique,but the existing membrane separation level still needs to be improved.Aquaporin（AQP）is a transmembrane protein with excellent water permeability and single selectivity.If the aquaporin can be introduced into the membrane and stably existed,the separation level of the existing membrane will be greatly improved,and it is expected to open a new direction for the forward osmosis field.In this paper,a high-performance aquaporin biomimetic membrane was prepared by interfacial polymerization and its preparation and properties was researched.Meanwhile,with the aid of heuristic dynamic polymerization method,the atomic models of PA membrane and AQP/PA membrane were innovatively constructed to analyze the microstructure of membrane and the mass transfer process of water molecules in the membrane.Finally,the anti-pollution performance of ABM membrane was investigated.A polysulfone-polyamide forward osmosis composite membrane（TFC membrane）was prepared by the interfacial polymerization method.The study found that the TFC membrane with 3.5 wt%m-phenylenediamine（MPD）and 0.15 wt%m-phenyltriformyl chloride（TMC）,the polymerization time was 40 s,n-hexane was used as organic solvent,heat treatment temperature was higher than 65℃and1.0 wt%dimethyl sulfoxide（DMSO）was added into MPD solution,the prepared TFC membrane exhibited good separation performance,the water flux and reverse salt flux of which were 13.45 L m^-2h^-1 and 2.01 g m^-2h^-1,respectively.At the same time,it was found that the heat treatment temperature was closely related to the boiling point of the organic phase.Adding DMSO or DMF in the aqueous phase can promote the two-phase miscibility and improve the water permeability of the membrane.In addition,the molecular mass transfer process of water molecules in the polyamide layer was studied by molecular dynamics simulation.Firstly,the polyamide（PA）membrane atomic model was constructed by dynamic polymerization.The model structure parameters were basically consistent with laboratory measurements and literature reports,which confirmed the rationality of the model.The number of hydrogen bonds in the membrane was less than that of the main body of the water phase.Whatever,the hydrogen bonds mainly occurred between oxygen and hydrogen atoms pairs,the distance and angle of hydrogen bonds between the water molecules and polyamide were larger than that between the water molecules.There was a coherent and stable hydrogen bond network structure in the membrane.It can be seen that the cross-linked structure in the PA membrane had a certain restrictive effect on the migration of water molecules,and the water molecules migrated in the PA membrane with the help of hydrogen bonding network.Based on the optimization of TFC membrane preparation process,AQP was embedded into lipid by rehydration dialysis method to prepare AQP lipoprotein vesicles,which were then encapsulated in polyamide selective layer by interfacial polymerization to obtain aquaporin forward osmosis composite membrane（ABM）.The results showed that the particle size of AQP lipoprotein vesicles was near 90 nm,and the permeability of AQP lipoprotein was as high as 523.58μm s^?1,showing high water permeability.Through the study of the preparation strategy of the aquaporin forward osmosis composite membrane,it was found that direct polymerization was helpful to obtain better membrane separation performance compared with stepwise polymerization.The effects of liposome concentration,AQP/liposome ratio,AQP liposome concentration and post-treatment on membrane forward osmotic performance were studied.Among them,the ratio of AQP/liposome and the concentration of AQP lipoprotein had more significant effects on water flux and reverse salt flux,respectively.At the same time,the optimization of membrane preparation process showed that the water flux of ABM membrane reached 22.31 L m^-2 h^-1 after Na OCl activation and heat treatment at70℃,when the AQP/liposome ratio was 1:200,AQP lipoprotein concentration was 0.5 mg/L,which was about 2 times of TFC membrane.The intrinsic structural parameters A,B and S of ABM-1membrane were 0.73 L m^-2 h^-1 bar^-1、0.08 m^-2 h^-1 and 153μm,respectively,which proved that the AQP forward osmosis composite membrane with excellent separation performance was successfully prepared.In the AQP/PA membrane microstructure model and molecular dynamics analysis,it wasfound that the AQP secondary structure showed a stable state in the simulation,maintaining a good structural conformation and biological activity.Asn76,His180 and Asn192 on the inner wall of the water hole channel had higher RMSF values and showed greater flexibility,which had a good targeted mass transfer effect on water molecules.Compared with PA membrane model,AQP/PA membrane model had more O_w-O_w and O_w-H_w hydrogen bonds and coordination number,and there were a lot of hydrogen bonds and water molecules near the water pore channel of AQP.According to MSD curve,the water molecule diffusion coefficients of PA membrane and AQP/PA membrane were calculated to be 0.481×10^-5 nm² ps^-1 and 6.085×10^-5 nm²ps^-1,respectively.It can be seen that the water-passing mechanism of AQP was closely related to the special pore structure and amino acid residues.AQP could provide a rapid transport channel for water molecules,thereby significantly increasing the diffusion coefficient of water molecules.Finally,the anti-fouling performance of ABM membrane was investigated,and sodium alginate,bovine serum albumin and reactive dye were selected as representative organic pollutants.The result showed that ABM membrane had better anti-pollution performance than TFC membrane,which was related to its better hydrophilicity and water pore channel.The increase of ions in feed solution and the presence of Ca²⁺accelerated the deposition of sodium alginate and BSA pollutants on the membrane surface.After 24h pollution-cleaning operation,the ABM membrane could concentrate the simulated dye wastewater twice,which was higher than that of the TFC membrane.At the same time,simple physical cleaning restored the water flux to about 85%and maintained a high retention rate of organic matter.In addition,the ABM membrane had a better ability to withstand the cleaning of acid and alkali solutions,but SDS and TX-100 cleaning led to the decrease of ABM membrane selectivity.It can be seen that ABM membrane had a wide application prospect as a new type of high flux and anti-pollution new forward osmosis membrane.