Preparation And Performance Of Go/CNC Polyamide Thin-film Nanocomposite Nanofiltration Membrane

Thin film composite（TFC）nanofiltration membrane has been widely used for its excellent separation performance,simple preparation and easy optimal regulation.However,in the actual use process,it still faces the problems of permeability-selectivity trade-off effect restrict,easy contamination and poor chlorine resistance,which restrict its further development.To solve the above problems,cellulose nanocrystalline（CNC）was used to modify graphene oxide（GO）to prepare a novel GO/CNC nanocomposite.It was introduced into the polyamide（PA）separation layer of composite nanofiltration membrane through interfacial polymerization,aiming to provide a theoretical basis for the performance improvement of low cost and high performance composite nanofiltration membrane.The main research contents and results are as follows.（1）The properties of GO/CNC nanocomposite were investigated by adding different ratios of GO during the acidysis process of CNC.The results showed that CNC was well combined with GO in the way of covering the surface layer and embedding the lamellae,and presented the network layered structure with the increase of the proportion of CNC.The characteristic peaks of GO and CNC existed in the XRD and FTIR spectra,indicating the successful combination of GO/CNC,and due to their interaction,the position and strength of some peaks changed.In addition,the layer spacing and electronegativity of GO in nanocomposite increased significantly co MPared with pure GO.When the mass ratio of GO to CNC was 1:25,the layer spacing increased from 0.88nm of pure GO to 0.93nm,and the zeta potential reached-56.3 m V,which significantly improved the dispersion stability compared with pure GO.（2）GO,CNC and GO/CNC nanocomposite were uniformly dispersed in piperazine aqueous solution respectively,and interfacial polymerization was performed with trimesoyl chloride to prepare composite nanofiltration membranes.The effects of different nanoparticles on the surface morphology,structural properties and separation performance of PA-TFC membranes were investigated comparatively.The results showed that the GO/CNC modified membrane had more obvious convex fold structure,higher roughness as well as hydrophilicity compared with GO and CNC single modified material.In addition,the lamellar spacing of GO in the nanocomposite was increased,which provided an additional transmission channel for the transmembrane process of water molecules.When the GO/CNC addition amount was 0.005 wt%,the pure water flux of the composite nanofiltration membrane reached a maximum 38.45L/（m²·h）,which was 84.86%and 53.92%higher than that of PA-TFC membrane and GO modified membrane respectively.The Na₂SO₄ and Na Cl rejection were 95.47%and 6.65%respectively,which exhibited enhanced Na₂SO₄/Na Cl separation selectivity.（3）The operation stability,dye separation performance,anti-fouling property and chlorine resistance of GO/CNC（0.005 wt%）membranes were evaluated.The results showed that the modified membrane maintained relatively stable permeation flux and Na₂SO₄ rejection during high pressure（0.6～1.0 MPa）and 48 h continuous operation.Co MPared with the PA-TFC membrane,the permeation flux of Congo red,Methylene blue and Rhodamine B increased by 80.63%,89.02%and 94.86%respectively,without sacrificing their separation performance.The dynamic contamination test of bovine albumin showed that the flux decay rate of the modified membrane was 33.10%after28 h operation,which was much lower than that of PA-TFC membrane（48.47%）.The flux recovery rate can reach more than 79%after online cleaning,showing great anti-fouling performance.After being immersed in Na Cl O solution（p H=4）with an available chlorine content of 4000 mg/L,the membrane surface still retains the polyamide layer structure without obvious defects.Under the chlorine intensity of16,000 mg/L·h,the normalized membrane flux increased by only 13%,accompanied with a decrease of the normalized Na₂SO₄ rejection from 100%to 95%,showing a better chlorine resistance performance.