Preparation And Characterization Of Novel Forward Osmosis Membrane Incorporated With Sulfonated Carbon Nanotubes

At present,The growing problems of water resources and energy has already attracted people's attention.Compared to ordinary water treatment processes,membrane separation process has the advantages of low energy consumption and low pollution,therefore,it plays an important role in the mitigation of water resources and energy issues.Among them,the forward osmosis(FO)process has advantages such as high purity of pure water and low degree of membrane fouling since no external pressure is required,only the osmotic pressure difference between the solutions is used as the mass transfer power.Right now,FO has shown its potential in many fields such as seawater desalination and high-salt wastewater treatment,and has gradually entered commercial use.The FO membrane is an indispensable part of FO process.An excellent FO membrane can provide more stable and better permeability for the FO process,so it is very important for the modification of FO membrane.Carbon nanotubes are one-dimensional nanomaterials with excellent water transport properties and have very important application potential in the field of membrane separation.However,pure carbon nanotubes have poor hydrophilicity and ofl:en fail to achieve satisfactory results when used as a separation membrane modification material.In this study,the pure carbon nanotubes were functionalized to improve their hydrophilicity,and then the modified carbon nanotubes were separately added into the PSF support layer and the PA active layer of FO membrane to explore the overall performance and analyze the mechanism.The main research work and content of this paper have the following three points.1:In this paper,the sulfonic acid groups were grafted onto the surface of pure carbon nanotubes by in-situ polymerization of sodium polystyrene sulfonate.The prepared sulfonated carbon nanotubes(SCNTs)were characterized by infrared characterization of sulfonate groups.The styrene sulfonic acid group which decomposed by heat was analyzed by TGA thermogravimetric loss.S element was also identified by XPS.The above can be comprehensively proved that carbon nanotubes were successfully sulfonated.2:The FO membmae with active layer SCNTs content of 0,100,200,400 and 600 ppm was successfully prepared by interfacial polymerization.The effects of the addition of SCNTs on the properties of FO membranes were investigated by infrared,contact angle,SEM and AFM.The results show that the active layer surface of FO membrane which was modified by SCNTs owns enhanced hydrophilicity,reduced roughness and more compact surface morphology.According to the FO performance test,the FO flux of SCNTs modified membrane is significantly higher than that of the unmodified FO membrane,and reaches a maximum of 37.43 LMH at 400 ppm(2 M NaCI as draw solution).Water permeability and salt permeability also changed with the addition of SCNTs.When the addition amount was 400 ppm,the water permeability was 2.29 LMH bar-1,which was the highest.The antibacterial property of the active layer-modified FO membrane was also measured.The results showed that the 400 ppm SCNTs modified FO membrane had the lowest bacterial load cultured by the E.coli and the load thickness was only 8 ?m,which was much lower than that of the unmodified membrane's 24 ?m under the same conditions.3:The FO membrane with support layer SCNTs content of 0,0.05%,0.1%,0.15%and 0.2%was successfully prepared by phase inversion method.It is obtained from the contact angle analysis that the addition of SCNTs simultaneously reduees the contact angle of the support layer and the active layer,means enhanced hydrophilicity.According to the SEM analysis of the support layer cross-section structure,it is found that the modified support layer void structure is more loose,and the same result can be obtained from the porosity and structural coefficient.After calculation,the porosity of the modified support layer increases,and reaches a maximum of 85.6%when the content of SCNTs is 0.15%,while the unmodified FO film is only 77.3%.The structural coefficient also reduced from 352 ?m to 270 ?m.In the FO performance test,the membrane flux increased with the increase of SCNTs content,and reached the maximum water flux of 37.25 LMH at 0.15%.The water permeability also showed the same trend,from the unmodified 1.45 LMH bar-1 increased to 0.15%LMH bar-1 at 0.15%,demonstrating superior FO performance after modification.