| The desalination of brackish water has become one of the effective ways to solve the current shortage of fresh water resources at home and abroad and to provide clean and safe water for life and production.Nanofiltration membrane has established its important position in the field of brackish water desalination with its low operating cost and superior retention performance.However,the traditional thin film composite（TFC）nanofiltration membrane has a"trade-off"effect between permeability and selectivity,and the existence of the"trade-off"effect limits the further development of nanofiltration membranes.In addition,nanofiltration membranes also face problems such as concentration polarization and membrane fouling.Membrane fouling will cause the attenuation of permeate flux and shorten the service life of the membrane.Therefore,it is particularly important to construct a new type of pollution-resistant nanofiltration membrane with high permeability without sacrificing selectivity.Molybdenum disulfide（Mo S2）nanosheets have excellent electronegativity,mechanical properties and pollution resistance,and have broad application prospects in the field of membrane technology.This topic selects Mo S2 nanosheets as the modified material,and constructs composite nanofiltration membranes through the modification of polyamide active layer and the introduction of interlayer.Various characterization methods were used to systematically investigate the effects of adding Mo S2 nanosheets at different levels on the physical and chemical properties,permeability/salt interception performance and antifouling performance of the composite nanofiltration membrane,and explore the treatment effect of the composite nanofiltration membrane on the actual brackish water.First,the polyethersulfone ultrafiltration membrane is selected as the bottom membrane,and the Mo S2 nanosheets are doped into the aqueous monomer for interfacial polymerization to construct a thin-film nanocomposite membrane（TFN membrane）.Investigate the influence of Mo S2 nanosheets doped in the aqueous phase interface polymerization on the physicochemical properties and permeation/separation performance of TFC membranes.The results show that as the concentration of the water phase doped Mo S2 nanosheets increases to 0.01wt%,the surface roughness,hydrophilicity and electronegativity of the constructed TFN membranes have all been increased.Compared with the control TFC membrane,the pure water flux of the TFN-W-0.01 membrane constructed by the aqueous phase doped nanosheets increased by 40%,the salt rejection performance was slightly improved,and the rejection rate of sodium sulfate was increased to 98.39%.The rejection rate of sodium chloride was increased to 27.78%.Secondly,the Mo S2 nanosheets were doped into the oil phase monomer for interfacial polymerization to construct the TFN membrane.The results show that when the loading of Mo S2 nanosheets in the organic phase reaches 0.001wt%,the water flux of the TFN-O-0.001 membrane increases by about 30%compared with the pure TFC membrane.Its salt-cutting performance has also been enhanced.In addition,compared with the TFN-W-0.01 membrane,the TFN-O-0.001 membrane can exhibit superior permeability and salt rejection under extremely low loadings.Then,using the means of introducing the interlayer,the Mo S2 nanosheets are suction filtered to form a composite nanofiltration membrane by the interface polymerization on the bottom membrane.The results show that when the loading of nanosheets is 0.8 mg,the TFC-0.8Mo S2 nanofiltration membrane exhibits the best performance.Its pure water permeation flux is 12.16 LMH/Bar,which is about 51%higher than the control TFC membrane.The retention rate of the membrane for sodium sulfate is 98.40%,and the retention rate for sodium chloride is 26.39%.In addition,the antifouling performance of the composite nanofiltration membrane constructed with the aqueous phase doped Mo S2 nanosheets,the oil phase doped Mo S2nanosheets,and Mo S2 nanosheets as the interlayer under the optimal gradient was investigated.It was found that compared with TFC membrane,the antifouling performance of these three Mo S2 nanosheet composite nanofiltration membranes have been improved.Subsequently,the treatment effect of the Mo S2 nanosheet composite nanofiltration membranes on the actual brackish water treatment was investigated,and antifouling performance of the actual water was evaluated.The results show that compared with the TFC membrane,these three Mo S2 nanosheet composite nanofiltration membranes have improved the removal effects of conventional anions,cations and UV254 in brackish water,and the antifouling performance has also been improved. |
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