Preparation And Performance Of Composite Nanofiltration Membrane With Multi-functional Layers Based On Polyelectrolyte/GO Control

As a kind of membrane separation technology,nanofiltration?NF?is widely used in water treatment.However,in practical applications,nanofiltration process generally is faced with the problems of membrane fouling and permeation flux reduction in complex separation environments.Therefore,this paper is focused on the preparation methods and materials of nanofiltration membranes to obtain nanofiltration membranes with superior separation and anti-pollution performance,and promote the wide practical application of nanofiltration membranes.Composite nanofiltration membrane with multi-functional layers based on polyelectrolyte/GO control was prepared through combined the layer-by-layer?LBL?self-assemblyandinterfacialpolymerization?IP?methods.Poly?diallyldimethylammonium chloride??PDDA?and poly?sodium 4-styrenesulfonate??PSS?were assembled together based on adsorption deposition to form polyelectrolyte multilayers on modified polyacrylonitrile?hPAN?substrate via layer-by-layer.Then,a polyamide?PA?layer was fabricated by interfacial polymerization of m-phenylenediamine?MPD?and trimesoyl chloride?TMC?to acquire a PEC-PA nanofiltration membrane with multi-functional layers.After further modified by using graphene oxide?GO?,the PSS solution was replaced by the GO-PSS blending solution.PEC/GO-PA nanofiltration membrane with better performance was obtained by the same method as PEC-PA nanofiltration membrane.Through analyzing the performance of the composite nanofiltration membrane with multi-functional layers in depth,the following results were obtained:?1?The optimal conditions of PEC-PA nanofiltration membrane:concentration of PDDA solution was 1.50 g/L,concentration of NaCl was 1.5 mol/L,concentration of PSS solution was 1.25 g/L,concentration of NaCl was 0.5 mol/L,polyelectrolyte monolayer deposition time was 20 min,and polyelectrolyte deposition layers were 2.5layers.The mass fraction of MPD was 0.4 wt%,the immersion time was 2 min,the mass fraction of TMC was 0.06 wt%,the polymerization time was 2.5 min,and the heat treatment time and temperature were 15 min and 60°C,respectively.Under operating pressure 0.8 MPa,the rejection rate of 2.0 g/L magnesium sulfate?MgSO₄?solution was about 98.44%,and permeation flux was 28.00 L/?m²·h?.With increase in rejection rate,the permeation flux of PEC-PA nanofiltration membrane was about 75%higher than that of the PA nanofiltration membrane.?2?The optimal conditions of PEC/GO-PA nanofiltration membrane obtained on the basis of PEC-PA nanofiltration membrane are as follows:the concentration of the GO solution in the PSS-GO blending solution was 1.0 g/L,concentration of NaCl was0.5 mol/L and the pH was 4.5.Under operating pressure 0.8 MPa,the rejection rate of2.0 g/L MgSO₄ solution was about 96.92%,and permeation flux was 35.64 L/?m²·h?.PEC/GO-PA nanofiltration membrane had increase in rejection rate,and its permeation flux was higher than PA nanofiltration membrane and PEC-PA nanofiltration membrane about 122%and 27%,respectively.?3?The results of scanning electron microscope?SEM?and X-ray diffractometer?XRD?showed that GO was successfully added in PEC/GO-PA nanofiltration membrane.The characteristics of membrane surface potential and contact angle indicated by an asymmetric clamping cell and a goniometer confirmed that the effectiveness of polyelectrolyte and GO in preparing PEC-PA and PEC/GO-PA nanofiltration membranes.?4?The separation performance of two composite nanofiltration membranes with multi-functional layers and PA nanofiltration membrane prepared through IP for four kinds of inorganic salts?2.0 g/L?was evaluated.The results showed that the retention rate of three nanofiltration membranes was Na₂SO₄>MgSO₄>MgCl₂>NaCl,which is a typical separation characteristic of negatively charged nanofiltration membrane.The permeation flux of the three nanofiltration membranes was PEC/GO-PA>PEC-PA>PA.?5?The typical organic pollutants bovine serum albumin?BSA?,alginic acid?SA?and humic acid?HA?were selected to conduct anti-fouling filtration experiments of nanofiltration membranes.The microscopic force of nanofiltration membrane and the above three pollutants were determined by AFM combined with self-made colloidal probe.By combining the flux of pollution filtration with microforce analysis,it can be drawn that due to the stepwise regulation of polyelectrolyte and GO,the hydrophilicity and the negative chargeability of the modified nanofiltration membrane was gradually enhanced,the anti-pollution performance of the modified nanofiltration membrane was enhanced.In general,the anti-pollution performance of the three nanofiltration membranes was PEC/GO-PA>PEC-PA>PA,the pollution trend of pollutants on three nanofiltration membranes was HA<SA<BSA.